thodg/libgit2

diff --git a/src/alloc.c b/src/alloc.c
index 51c4d80..6972e7b 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -6,10 +6,16 @@
  */
 
 #include "alloc.h"
+#include "runtime.h"
 
 #include "allocators/stdalloc.h"
 #include "allocators/win32_crtdbg.h"
 
+#if defined(GIT_MSVC_CRTDBG)
+# include "win32/w32_stack.h"
+# include "win32/w32_crtdbg_stacktrace.h"
+#endif
+
 git_allocator git__allocator;
 
 static int setup_default_allocator(void)
@@ -21,8 +27,24 @@ static int setup_default_allocator(void)
 #endif
 }
 
+#if defined(GIT_MSVC_CRTDBG)
+static void allocator_global_shutdown(void)
+{
+	git_win32__crtdbg_stacktrace_cleanup();
+	git_win32__stack_cleanup();
+}
+#endif
+
 int git_allocator_global_init(void)
 {
+#if defined(GIT_MSVC_CRTDBG)
+	git_win32__crtdbg_stacktrace_init();
+	git_win32__stack_init();
+
+	if (git_runtime_shutdown_register(allocator_global_shutdown) < 0)
+		return -1;
+#endif
+
 	/*
 	 * We don't want to overwrite any allocator which has been set before
 	 * the init function is called.
diff --git a/src/allocators/win32_crtdbg.c b/src/allocators/win32_crtdbg.c
index 1187e2f..c726268 100644
--- a/src/allocators/win32_crtdbg.c
+++ b/src/allocators/win32_crtdbg.c
@@ -9,6 +9,7 @@
 
 #if defined(GIT_MSVC_CRTDBG)
 
+#include "win32/w32_stack.h"
 #include "win32/w32_crtdbg_stacktrace.h"
 
 static void *crtdbg__malloc(size_t len, const char *file, int line)
diff --git a/src/errors.c b/src/errors.c
index 8570226..d4da50d 100644
--- a/src/errors.c
+++ b/src/errors.c
@@ -7,7 +7,7 @@
 
 #include "common.h"
 
-#include "global.h"
+#include "threadstate.h"
 #include "posix.h"
 #include "buffer.h"
 
@@ -22,18 +22,18 @@ static git_error g_git_oom_error = {
 
 static void set_error_from_buffer(int error_class)
 {
-	git_error *error = &GIT_GLOBAL->error_t;
-	git_buf *buf = &GIT_GLOBAL->error_buf;
+	git_error *error = &GIT_THREADSTATE->error_t;
+	git_buf *buf = &GIT_THREADSTATE->error_buf;
 
 	error->message = buf->ptr;
 	error->klass = error_class;
 
-	GIT_GLOBAL->last_error = error;
+	GIT_THREADSTATE->last_error = error;
 }
 
 static void set_error(int error_class, char *string)
 {
-	git_buf *buf = &GIT_GLOBAL->error_buf;
+	git_buf *buf = &GIT_THREADSTATE->error_buf;
 
 	git_buf_clear(buf);
 	if (string) {
@@ -46,7 +46,7 @@ static void set_error(int error_class, char *string)
 
 void git_error_set_oom(void)
 {
-	GIT_GLOBAL->last_error = &g_git_oom_error;
+	GIT_THREADSTATE->last_error = &g_git_oom_error;
 }
 
 void git_error_set(int error_class, const char *fmt, ...)
@@ -64,7 +64,7 @@ void git_error_vset(int error_class, const char *fmt, va_list ap)
 	DWORD win32_error_code = (error_class == GIT_ERROR_OS) ? GetLastError() : 0;
 #endif
 	int error_code = (error_class == GIT_ERROR_OS) ? errno : 0;
-	git_buf *buf = &GIT_GLOBAL->error_buf;
+	git_buf *buf = &GIT_THREADSTATE->error_buf;
 
 	git_buf_clear(buf);
 	if (fmt) {
@@ -97,7 +97,7 @@ void git_error_vset(int error_class, const char *fmt, va_list ap)
 
 int git_error_set_str(int error_class, const char *string)
 {
-	git_buf *buf = &GIT_GLOBAL->error_buf;
+	git_buf *buf = &GIT_THREADSTATE->error_buf;
 
 	assert(string);
 
@@ -118,9 +118,9 @@ int git_error_set_str(int error_class, const char *string)
 
 void git_error_clear(void)
 {
-	if (GIT_GLOBAL->last_error != NULL) {
+	if (GIT_THREADSTATE->last_error != NULL) {
 		set_error(0, NULL);
-		GIT_GLOBAL->last_error = NULL;
+		GIT_THREADSTATE->last_error = NULL;
 	}
 
 	errno = 0;
@@ -131,13 +131,13 @@ void git_error_clear(void)
 
 const git_error *git_error_last(void)
 {
-	return GIT_GLOBAL->last_error;
+	return GIT_THREADSTATE->last_error;
 }
 
 int git_error_state_capture(git_error_state *state, int error_code)
 {
-	git_error *error = GIT_GLOBAL->last_error;
-	git_buf *error_buf = &GIT_GLOBAL->error_buf;
+	git_error *error = GIT_THREADSTATE->last_error;
+	git_buf *error_buf = &GIT_THREADSTATE->error_buf;
 
 	memset(state, 0, sizeof(git_error_state));
 
diff --git a/src/filter.c b/src/filter.c
index 09b57dc..86db5a5 100644
--- a/src/filter.c
+++ b/src/filter.c
@@ -11,7 +11,7 @@
 #include "futils.h"
 #include "hash.h"
 #include "repository.h"
-#include "global.h"
+#include "runtime.h"
 #include "git2/sys/filter.h"
 #include "git2/config.h"
 #include "blob.h"
@@ -206,7 +206,7 @@ int git_filter_global_init(void)
 			GIT_FILTER_IDENT, ident, GIT_FILTER_IDENT_PRIORITY) < 0)
 		error = -1;
 
-	git__on_shutdown(git_filter_global_shutdown);
+	error = git_runtime_shutdown_register(git_filter_global_shutdown);
 
 done:
 	if (error) {
diff --git a/src/futils.c b/src/futils.c
index 8c0f008..2ad8a1b 100644
--- a/src/futils.c
+++ b/src/futils.c
@@ -7,8 +7,9 @@
 
 #include "futils.h"
 
-#include "global.h"
+#include "runtime.h"
 #include "strmap.h"
+#include "hash.h"
 #include <ctype.h>
 #if GIT_WIN32
 #include "win32/findfile.h"
diff --git a/src/global.c b/src/global.c
deleted file mode 100644
index 9fe8cd5..0000000
--- a/src/global.c
+++ /dev/null
@@ -1,363 +0,0 @@
-/*
- * Copyright (C) the libgit2 contributors. All rights reserved.
- *
- * This file is part of libgit2, distributed under the GNU GPL v2 with
- * a Linking Exception. For full terms see the included COPYING file.
- */
-
-#include "global.h"
-
-#include "alloc.h"
-#include "hash.h"
-#include "sysdir.h"
-#include "filter.h"
-#include "merge_driver.h"
-#include "pool.h"
-#include "streams/registry.h"
-#include "streams/mbedtls.h"
-#include "streams/openssl.h"
-#include "thread-utils.h"
-#include "git2/global.h"
-#include "transports/ssh.h"
-
-#if defined(GIT_MSVC_CRTDBG)
-#include "win32/w32_stack.h"
-#include "win32/w32_crtdbg_stacktrace.h"
-#endif
-
-git_mutex git__mwindow_mutex;
-
-typedef int (*git_global_init_fn)(void);
-
-static git_global_init_fn git__init_callbacks[] = {
-	git_allocator_global_init,
-	git_hash_global_init,
-	git_sysdir_global_init,
-	git_filter_global_init,
-	git_merge_driver_global_init,
-	git_transport_ssh_global_init,
-	git_stream_registry_global_init,
-	git_openssl_stream_global_init,
-	git_mbedtls_stream_global_init,
-	git_mwindow_global_init,
-	git_pool_global_init
-};
-
-static git_global_shutdown_fn git__shutdown_callbacks[ARRAY_SIZE(git__init_callbacks)];
-
-static git_atomic git__n_shutdown_callbacks;
-static git_atomic git__n_inits;
-char *git__user_agent;
-char *git__ssl_ciphers;
-
-void git__on_shutdown(git_global_shutdown_fn callback)
-{
-	int count = git_atomic_inc(&git__n_shutdown_callbacks);
-	assert(count <= (int) ARRAY_SIZE(git__shutdown_callbacks) && count > 0);
-	git__shutdown_callbacks[count - 1] = callback;
-}
-
-static void git__global_state_cleanup(git_global_st *st)
-{
-	if (!st)
-		return;
-
-	git__free(st->error_t.message);
-	st->error_t.message = NULL;
-}
-
-static int init_common(void)
-{
-	size_t i;
-	int ret;
-
-	/* Initialize the CRT debug allocator first, before our first malloc */
-#if defined(GIT_MSVC_CRTDBG)
-	git_win32__crtdbg_stacktrace_init();
-	git_win32__stack_init();
-#endif
-
-	/* Initialize subsystems that have global state */
-	for (i = 0; i < ARRAY_SIZE(git__init_callbacks); i++)
-		if ((ret = git__init_callbacks[i]()) != 0)
-			break;
-
-	GIT_MEMORY_BARRIER;
-
-	return ret;
-}
-
-static void shutdown_common(void)
-{
-	int pos;
-
-	/* Shutdown subsystems that have registered */
-	for (pos = git_atomic_get(&git__n_shutdown_callbacks);
-		pos > 0;
-		pos = git_atomic_dec(&git__n_shutdown_callbacks)) {
-
-		git_global_shutdown_fn cb = git__swap(
-			git__shutdown_callbacks[pos - 1], NULL);
-
-		if (cb != NULL)
-			cb();
-	}
-
-	git__free(git__user_agent);
-	git__free(git__ssl_ciphers);
-}
-
-/**
- * Handle the global state with TLS
- *
- * If libgit2 is built with GIT_THREADS enabled,
- * the `git_libgit2_init()` function must be called
- * before calling any other function of the library.
- *
- * This function allocates a TLS index (using pthreads
- * or the native Win32 API) to store the global state
- * on a per-thread basis.
- *
- * Any internal method that requires global state will
- * then call `git__global_state()` which returns a pointer
- * to the global state structure; this pointer is lazily
- * allocated on each thread.
- *
- * Before shutting down the library, the
- * `git_libgit2_shutdown` method must be called to free
- * the previously reserved TLS index.
- *
- * If libgit2 is built without threading support, the
- * `git__global_statestate()` call returns a pointer to a single,
- * statically allocated global state. The `git_thread_`
- * functions are not available in that case.
- */
-
-/*
- * `git_libgit2_init()` allows subsystems to perform global setup,
- * which may take place in the global scope.  An explicit memory
- * fence exists at the exit of `git_libgit2_init()`.  Without this,
- * CPU cores are free to reorder cache invalidation of `_tls_init`
- * before cache invalidation of the subsystems' newly written global
- * state.
- */
-#if defined(GIT_THREADS) && defined(GIT_WIN32)
-
-static DWORD _fls_index;
-static volatile LONG _mutex = 0;
-
-static void WINAPI fls_free(void *st)
-{
-	git__global_state_cleanup(st);
-	git__free(st);
-}
-
-static int synchronized_threads_init(void)
-{
-	int error;
-
-	if ((_fls_index = FlsAlloc(fls_free)) == FLS_OUT_OF_INDEXES)
-		return -1;
-
-	git_threads_init();
-
-	if (git_mutex_init(&git__mwindow_mutex))
-		return -1;
-
-	error = init_common();
-
-	return error;
-}
-
-int git_libgit2_init(void)
-{
-	int ret;
-
-	/* Enter the lock */
-	while (InterlockedCompareExchange(&_mutex, 1, 0)) { Sleep(0); }
-
-	/* Only do work on a 0 -> 1 transition of the refcount */
-	if ((ret = git_atomic_inc(&git__n_inits)) == 1) {
-		if (synchronized_threads_init() < 0)
-			ret = -1;
-	}
-
-	/* Exit the lock */
-	InterlockedExchange(&_mutex, 0);
-
-	return ret;
-}
-
-int git_libgit2_shutdown(void)
-{
-	int ret;
-
-	/* Enter the lock */
-	while (InterlockedCompareExchange(&_mutex, 1, 0)) { Sleep(0); }
-
-	/* Only do work on a 1 -> 0 transition of the refcount */
-	if ((ret = git_atomic_dec(&git__n_inits)) == 0) {
-		shutdown_common();
-
-		FlsFree(_fls_index);
-		git_mutex_free(&git__mwindow_mutex);
-
-#if defined(GIT_MSVC_CRTDBG)
-		git_win32__crtdbg_stacktrace_cleanup();
-		git_win32__stack_cleanup();
-#endif
-	}
-
-	/* Exit the lock */
-	InterlockedExchange(&_mutex, 0);
-
-	return ret;
-}
-
-git_global_st *git__global_state(void)
-{
-	git_global_st *ptr;
-
-	assert(git_atomic_get(&git__n_inits) > 0);
-
-	if ((ptr = FlsGetValue(_fls_index)) != NULL)
-		return ptr;
-
-	ptr = git__calloc(1, sizeof(git_global_st));
-	if (!ptr)
-		return NULL;
-
-	git_buf_init(&ptr->error_buf, 0);
-
-	FlsSetValue(_fls_index, ptr);
-	return ptr;
-}
-
-#elif defined(GIT_THREADS) && defined(_POSIX_THREADS)
-
-static pthread_key_t _tls_key;
-static pthread_mutex_t _init_mutex = PTHREAD_MUTEX_INITIALIZER;
-static pthread_once_t _once_init = PTHREAD_ONCE_INIT;
-int init_error = 0;
-
-static void cb__free_status(void *st)
-{
-	git__global_state_cleanup(st);
-	git__free(st);
-}
-
-static void init_once(void)
-{
-	if ((init_error = git_mutex_init(&git__mwindow_mutex)) != 0)
-		return;
-
-	pthread_key_create(&_tls_key, &cb__free_status);
-
-	init_error = init_common();
-}
-
-int git_libgit2_init(void)
-{
-	int ret, err;
-
-	if ((err = pthread_mutex_lock(&_init_mutex)) != 0)
-		return err;
-
-	ret = git_atomic_inc(&git__n_inits);
-	err = pthread_once(&_once_init, init_once);
-	err |= pthread_mutex_unlock(&_init_mutex);
-
-	if (err || init_error)
-		return err | init_error;
-
-	return ret;
-}
-
-int git_libgit2_shutdown(void)
-{
-	void *ptr = NULL;
-	pthread_once_t new_once = PTHREAD_ONCE_INIT;
-	int error, ret;
-
-	if ((error = pthread_mutex_lock(&_init_mutex)) != 0)
-		return error;
-
-	if ((ret = git_atomic_dec(&git__n_inits)) != 0)
-		goto out;
-
-	/* Shut down any subsystems that have global state */
-	shutdown_common();
-
-	ptr = pthread_getspecific(_tls_key);
-	pthread_setspecific(_tls_key, NULL);
-
-	git__global_state_cleanup(ptr);
-	git__free(ptr);
-
-	pthread_key_delete(_tls_key);
-	git_mutex_free(&git__mwindow_mutex);
-	_once_init = new_once;
-
-out:
-	if ((error = pthread_mutex_unlock(&_init_mutex)) != 0)
-		return error;
-
-	return ret;
-}
-
-git_global_st *git__global_state(void)
-{
-	git_global_st *ptr;
-
-	assert(git_atomic_get(&git__n_inits) > 0);
-
-	if ((ptr = pthread_getspecific(_tls_key)) != NULL)
-		return ptr;
-
-	ptr = git__calloc(1, sizeof(git_global_st));
-	if (!ptr)
-		return NULL;
-
-	git_buf_init(&ptr->error_buf, 0);
-	pthread_setspecific(_tls_key, ptr);
-	return ptr;
-}
-
-#else
-
-static git_global_st __state;
-
-int git_libgit2_init(void)
-{
-	int ret;
-
-	/* Only init subsystems the first time */
-	if ((ret = git_atomic_inc(&git__n_inits)) != 1)
-		return ret;
-
-	if ((ret = init_common()) < 0)
-		return ret;
-
-	return 1;
-}
-
-int git_libgit2_shutdown(void)
-{
-	int ret;
-
-	/* Shut down any subsystems that have global state */
-	if ((ret = git_atomic_dec(&git__n_inits)) == 0) {
-		shutdown_common();
-		git__global_state_cleanup(&__state);
-		memset(&__state, 0, sizeof(__state));
-	}
-
-	return ret;
-}
-
-git_global_st *git__global_state(void)
-{
-	return &__state;
-}
-
-#endif /* GIT_THREADS */
diff --git a/src/global.h b/src/global.h
deleted file mode 100644
index db41dad..0000000
--- a/src/global.h
+++ /dev/null
@@ -1,41 +0,0 @@
-/*
- * Copyright (C) the libgit2 contributors. All rights reserved.
- *
- * This file is part of libgit2, distributed under the GNU GPL v2 with
- * a Linking Exception. For full terms see the included COPYING file.
- */
-#ifndef INCLUDE_global_h__
-#define INCLUDE_global_h__
-
-#include "common.h"
-
-#include "mwindow.h"
-#include "hash.h"
-
-typedef struct {
-	git_error *last_error;
-	git_error error_t;
-	git_buf error_buf;
-	char oid_fmt[GIT_OID_HEXSZ+1];
-
-	/* On Windows, this is the current child thread that was started by
-	 * `git_thread_create`.  This is used to set the thread's exit code
-	 * when terminated by `git_thread_exit`.  It is unused on POSIX.
-	 */
-	git_thread *current_thread;
-} git_global_st;
-
-git_global_st *git__global_state(void);
-
-extern git_mutex git__mwindow_mutex;
-
-#define GIT_GLOBAL (git__global_state())
-
-typedef void (*git_global_shutdown_fn)(void);
-
-extern void git__on_shutdown(git_global_shutdown_fn callback);
-
-extern const char *git_libgit2__user_agent(void);
-extern const char *git_libgit2__ssl_ciphers(void);
-
-#endif
diff --git a/src/hash/sha1/win32.c b/src/hash/sha1/win32.c
index c736956..b1266cc 100644
--- a/src/hash/sha1/win32.c
+++ b/src/hash/sha1/win32.c
@@ -7,7 +7,7 @@
 
 #include "win32.h"
 
-#include "global.h"
+#include "runtime.h"
 
 #include <wincrypt.h>
 #include <strsafe.h>
@@ -129,7 +129,8 @@ int git_hash_sha1_global_init(void)
 	if ((error = hash_cng_prov_init()) < 0)
 		error = hash_cryptoapi_prov_init();
 
-	git__on_shutdown(sha1_shutdown);
+	if (!error)
+		error = git_runtime_shutdown_register(sha1_shutdown);
 
 	return error;
 }
diff --git a/src/libgit2.c b/src/libgit2.c
new file mode 100644
index 0000000..316d893
--- /dev/null
+++ b/src/libgit2.c
@@ -0,0 +1,361 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+
+#include "libgit2.h"
+
+#include <git2.h>
+#include "alloc.h"
+#include "cache.h"
+#include "common.h"
+#include "filter.h"
+#include "hash.h"
+#include "index.h"
+#include "merge_driver.h"
+#include "pool.h"
+#include "mwindow.h"
+#include "object.h"
+#include "odb.h"
+#include "refs.h"
+#include "runtime.h"
+#include "sysdir.h"
+#include "thread-utils.h"
+#include "threadstate.h"
+#include "git2/global.h"
+#include "streams/registry.h"
+#include "streams/mbedtls.h"
+#include "streams/openssl.h"
+#include "transports/smart.h"
+#include "transports/http.h"
+#include "transports/ssh.h"
+#include "win32/w32_stack.h"
+
+#ifdef GIT_OPENSSL
+# include <openssl/err.h>
+#endif
+
+#ifdef GIT_MBEDTLS
+# include <mbedtls/error.h>
+#endif
+
+/* Declarations for tuneable settings */
+extern size_t git_mwindow__window_size;
+extern size_t git_mwindow__mapped_limit;
+extern size_t git_mwindow__file_limit;
+extern size_t git_indexer__max_objects;
+extern bool git_disable_pack_keep_file_checks;
+
+char *git__user_agent;
+char *git__ssl_ciphers;
+
+static void libgit2_settings_global_shutdown(void)
+{
+	git__free(git__user_agent);
+	git__free(git__ssl_ciphers);
+}
+
+static int git_libgit2_settings_global_init(void)
+{
+	return git_runtime_shutdown_register(libgit2_settings_global_shutdown);
+}
+
+int git_libgit2_init(void)
+{
+	static git_runtime_init_fn init_fns[] = {
+		git_allocator_global_init,
+		git_threadstate_global_init,
+		git_threads_global_init,
+		git_hash_global_init,
+		git_sysdir_global_init,
+		git_filter_global_init,
+		git_merge_driver_global_init,
+		git_transport_ssh_global_init,
+		git_stream_registry_global_init,
+		git_openssl_stream_global_init,
+		git_mbedtls_stream_global_init,
+		git_mwindow_global_init,
+		git_pool_global_init,
+		git_libgit2_settings_global_init
+	};
+
+	return git_runtime_init(init_fns, ARRAY_SIZE(init_fns));
+}
+
+int git_libgit2_shutdown(void)
+{
+	return git_runtime_shutdown();
+}
+
+int git_libgit2_version(int *major, int *minor, int *rev)
+{
+	*major = LIBGIT2_VER_MAJOR;
+	*minor = LIBGIT2_VER_MINOR;
+	*rev = LIBGIT2_VER_REVISION;
+
+	return 0;
+}
+
+int git_libgit2_features(void)
+{
+	return 0
+#ifdef GIT_THREADS
+		| GIT_FEATURE_THREADS
+#endif
+#ifdef GIT_HTTPS
+		| GIT_FEATURE_HTTPS
+#endif
+#if defined(GIT_SSH)
+		| GIT_FEATURE_SSH
+#endif
+#if defined(GIT_USE_NSEC)
+		| GIT_FEATURE_NSEC
+#endif
+	;
+}
+
+static int config_level_to_sysdir(int config_level)
+{
+	int val = -1;
+
+	switch (config_level) {
+	case GIT_CONFIG_LEVEL_SYSTEM:
+		val = GIT_SYSDIR_SYSTEM;
+		break;
+	case GIT_CONFIG_LEVEL_XDG:
+		val = GIT_SYSDIR_XDG;
+		break;
+	case GIT_CONFIG_LEVEL_GLOBAL:
+		val = GIT_SYSDIR_GLOBAL;
+		break;
+	case GIT_CONFIG_LEVEL_PROGRAMDATA:
+		val = GIT_SYSDIR_PROGRAMDATA;
+		break;
+	default:
+		git_error_set(
+			GIT_ERROR_INVALID, "invalid config path selector %d", config_level);
+	}
+
+	return val;
+}
+
+const char *git_libgit2__user_agent(void)
+{
+	return git__user_agent;
+}
+
+const char *git_libgit2__ssl_ciphers(void)
+{
+	return git__ssl_ciphers;
+}
+
+int git_libgit2_opts(int key, ...)
+{
+	int error = 0;
+	va_list ap;
+
+	va_start(ap, key);
+
+	switch (key) {
+	case GIT_OPT_SET_MWINDOW_SIZE:
+		git_mwindow__window_size = va_arg(ap, size_t);
+		break;
+
+	case GIT_OPT_GET_MWINDOW_SIZE:
+		*(va_arg(ap, size_t *)) = git_mwindow__window_size;
+		break;
+
+	case GIT_OPT_SET_MWINDOW_MAPPED_LIMIT:
+		git_mwindow__mapped_limit = va_arg(ap, size_t);
+		break;
+
+	case GIT_OPT_GET_MWINDOW_MAPPED_LIMIT:
+		*(va_arg(ap, size_t *)) = git_mwindow__mapped_limit;
+		break;
+
+	case GIT_OPT_SET_MWINDOW_FILE_LIMIT:
+		git_mwindow__file_limit = va_arg(ap, size_t);
+		break;
+
+	case GIT_OPT_GET_MWINDOW_FILE_LIMIT:
+		*(va_arg(ap, size_t *)) = git_mwindow__file_limit;
+		break;
+
+	case GIT_OPT_GET_SEARCH_PATH:
+		if ((error = config_level_to_sysdir(va_arg(ap, int))) >= 0) {
+			git_buf *out = va_arg(ap, git_buf *);
+			const git_buf *tmp;
+
+			git_buf_sanitize(out);
+			if ((error = git_sysdir_get(&tmp, error)) < 0)
+				break;
+
+			error = git_buf_sets(out, tmp->ptr);
+		}
+		break;
+
+	case GIT_OPT_SET_SEARCH_PATH:
+		if ((error = config_level_to_sysdir(va_arg(ap, int))) >= 0)
+			error = git_sysdir_set(error, va_arg(ap, const char *));
+		break;
+
+	case GIT_OPT_SET_CACHE_OBJECT_LIMIT:
+		{
+			git_object_t type = (git_object_t)va_arg(ap, int);
+			size_t size = va_arg(ap, size_t);
+			error = git_cache_set_max_object_size(type, size);
+			break;
+		}
+
+	case GIT_OPT_SET_CACHE_MAX_SIZE:
+		git_cache__max_storage = va_arg(ap, ssize_t);
+		break;
+
+	case GIT_OPT_ENABLE_CACHING:
+		git_cache__enabled = (va_arg(ap, int) != 0);
+		break;
+
+	case GIT_OPT_GET_CACHED_MEMORY:
+		*(va_arg(ap, ssize_t *)) = git_cache__current_storage.val;
+		*(va_arg(ap, ssize_t *)) = git_cache__max_storage;
+		break;
+
+	case GIT_OPT_GET_TEMPLATE_PATH:
+		{
+			git_buf *out = va_arg(ap, git_buf *);
+			const git_buf *tmp;
+
+			git_buf_sanitize(out);
+			if ((error = git_sysdir_get(&tmp, GIT_SYSDIR_TEMPLATE)) < 0)
+				break;
+
+			error = git_buf_sets(out, tmp->ptr);
+		}
+		break;
+
+	case GIT_OPT_SET_TEMPLATE_PATH:
+		error = git_sysdir_set(GIT_SYSDIR_TEMPLATE, va_arg(ap, const char *));
+		break;
+
+	case GIT_OPT_SET_SSL_CERT_LOCATIONS:
+#ifdef GIT_OPENSSL
+		{
+			const char *file = va_arg(ap, const char *);
+			const char *path = va_arg(ap, const char *);
+			error = git_openssl__set_cert_location(file, path);
+		}
+#elif defined(GIT_MBEDTLS)
+		{
+			const char *file = va_arg(ap, const char *);
+			const char *path = va_arg(ap, const char *);
+			if (file)
+				error = git_mbedtls__set_cert_location(file, 0);
+			if (error && path)
+				error = git_mbedtls__set_cert_location(path, 1);
+		}
+#else
+		git_error_set(GIT_ERROR_SSL, "TLS backend doesn't support certificate locations");
+		error = -1;
+#endif
+		break;
+	case GIT_OPT_SET_USER_AGENT:
+		git__free(git__user_agent);
+		git__user_agent = git__strdup(va_arg(ap, const char *));
+		if (!git__user_agent) {
+			git_error_set_oom();
+			error = -1;
+		}
+
+		break;
+
+	case GIT_OPT_ENABLE_STRICT_OBJECT_CREATION:
+		git_object__strict_input_validation = (va_arg(ap, int) != 0);
+		break;
+
+	case GIT_OPT_ENABLE_STRICT_SYMBOLIC_REF_CREATION:
+		git_reference__enable_symbolic_ref_target_validation = (va_arg(ap, int) != 0);
+		break;
+
+	case GIT_OPT_SET_SSL_CIPHERS:
+#if (GIT_OPENSSL || GIT_MBEDTLS)
+		{
+			git__free(git__ssl_ciphers);
+			git__ssl_ciphers = git__strdup(va_arg(ap, const char *));
+			if (!git__ssl_ciphers) {
+				git_error_set_oom();
+				error = -1;
+			}
+		}
+#else
+		git_error_set(GIT_ERROR_SSL, "TLS backend doesn't support custom ciphers");
+		error = -1;
+#endif
+		break;
+
+	case GIT_OPT_GET_USER_AGENT:
+		{
+			git_buf *out = va_arg(ap, git_buf *);
+			git_buf_sanitize(out);
+			error = git_buf_sets(out, git__user_agent);
+		}
+		break;
+
+	case GIT_OPT_ENABLE_OFS_DELTA:
+		git_smart__ofs_delta_enabled = (va_arg(ap, int) != 0);
+		break;
+
+	case GIT_OPT_ENABLE_FSYNC_GITDIR:
+		git_repository__fsync_gitdir = (va_arg(ap, int) != 0);
+		break;
+
+	case GIT_OPT_GET_WINDOWS_SHAREMODE:
+#ifdef GIT_WIN32
+		*(va_arg(ap, unsigned long *)) = git_win32__createfile_sharemode;
+#endif
+		break;
+
+	case GIT_OPT_SET_WINDOWS_SHAREMODE:
+#ifdef GIT_WIN32
+		git_win32__createfile_sharemode = va_arg(ap, unsigned long);
+#endif
+		break;
+
+	case GIT_OPT_ENABLE_STRICT_HASH_VERIFICATION:
+		git_odb__strict_hash_verification = (va_arg(ap, int) != 0);
+		break;
+
+	case GIT_OPT_SET_ALLOCATOR:
+		error = git_allocator_setup(va_arg(ap, git_allocator *));
+		break;
+
+	case GIT_OPT_ENABLE_UNSAVED_INDEX_SAFETY:
+		git_index__enforce_unsaved_safety = (va_arg(ap, int) != 0);
+		break;
+
+	case GIT_OPT_SET_PACK_MAX_OBJECTS:
+		git_indexer__max_objects = va_arg(ap, size_t);
+		break;
+
+	case GIT_OPT_GET_PACK_MAX_OBJECTS:
+		*(va_arg(ap, size_t *)) = git_indexer__max_objects;
+		break;
+
+	case GIT_OPT_DISABLE_PACK_KEEP_FILE_CHECKS:
+		git_disable_pack_keep_file_checks = (va_arg(ap, int) != 0);
+		break;
+
+	case GIT_OPT_ENABLE_HTTP_EXPECT_CONTINUE:
+		git_http__expect_continue = (va_arg(ap, int) != 0);
+		break;
+
+	default:
+		git_error_set(GIT_ERROR_INVALID, "invalid option key");
+		error = -1;
+	}
+
+	va_end(ap);
+
+	return error;
+}
diff --git a/src/libgit2.h b/src/libgit2.h
new file mode 100644
index 0000000..6f92a83
--- /dev/null
+++ b/src/libgit2.h
@@ -0,0 +1,13 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+#ifndef INCLUDE_libgit2_h__
+#define INCLUDE_libgit2_h__
+
+extern const char *git_libgit2__user_agent(void);
+extern const char *git_libgit2__ssl_ciphers(void);
+
+#endif
diff --git a/src/merge_driver.c b/src/merge_driver.c
index 666349b..b1f5748 100644
--- a/src/merge_driver.c
+++ b/src/merge_driver.c
@@ -8,7 +8,7 @@
 #include "merge_driver.h"
 
 #include "vector.h"
-#include "global.h"
+#include "runtime.h"
 #include "merge.h"
 #include "git2/merge.h"
 #include "git2/sys/merge.h"
@@ -209,7 +209,7 @@ int git_merge_driver_global_init(void)
 			merge_driver_name__binary, &git_merge_driver__binary)) < 0)
 		goto done;
 
-	git__on_shutdown(git_merge_driver_global_shutdown);
+	error = git_runtime_shutdown_register(git_merge_driver_global_shutdown);
 
 done:
 	if (error < 0)
diff --git a/src/mwindow.c b/src/mwindow.c
index ac26452..a852d6b 100644
--- a/src/mwindow.c
+++ b/src/mwindow.c
@@ -10,7 +10,7 @@
 #include "vector.h"
 #include "futils.h"
 #include "map.h"
-#include "global.h"
+#include "runtime.h"
 #include "strmap.h"
 #include "pack.h"
 
@@ -29,26 +29,36 @@ size_t git_mwindow__window_size = DEFAULT_WINDOW_SIZE;
 size_t git_mwindow__mapped_limit = DEFAULT_MAPPED_LIMIT;
 size_t git_mwindow__file_limit = DEFAULT_FILE_LIMIT;
 
+/* Mutex to control access */
+git_mutex git__mwindow_mutex;
+
 /* Whenever you want to read or modify this, grab git__mwindow_mutex */
 git_mwindow_ctl git_mwindow__mem_ctl;
 
 /* Global list of mwindow files, to open packs once across repos */
 git_strmap *git__pack_cache = NULL;
 
-static void git_mwindow_files_free(void)
+static void git_mwindow_global_shutdown(void)
 {
 	git_strmap *tmp = git__pack_cache;
 
+	git_mutex_free(&git__mwindow_mutex);
+
 	git__pack_cache = NULL;
 	git_strmap_free(tmp);
 }
 
 int git_mwindow_global_init(void)
 {
+	int error;
+
 	assert(!git__pack_cache);
 
-	git__on_shutdown(git_mwindow_files_free);
-	return git_strmap_new(&git__pack_cache);
+	if ((error = git_mutex_init(&git__mwindow_mutex)) < 0 ||
+	    (error = git_strmap_new(&git__pack_cache)) < 0)
+	    return error;
+
+	return git_runtime_shutdown_register(git_mwindow_global_shutdown);
 }
 
 int git_mwindow_get_pack(struct git_pack_file **out, const char *path)
diff --git a/src/mwindow.h b/src/mwindow.h
index 1a391b0..7519fc3 100644
--- a/src/mwindow.h
+++ b/src/mwindow.h
@@ -13,6 +13,8 @@
 #include "map.h"
 #include "vector.h"
 
+extern git_mutex git__mwindow_mutex;
+
 typedef struct git_mwindow {
 	struct git_mwindow *next;
 	git_map window_map;
diff --git a/src/net.c b/src/net.c
index dbde626..ac1bc42 100644
--- a/src/net.c
+++ b/src/net.c
@@ -14,7 +14,7 @@
 #include "posix.h"
 #include "buffer.h"
 #include "http_parser.h"
-#include "global.h"
+#include "runtime.h"
 
 #define DEFAULT_PORT_HTTP  "80"
 #define DEFAULT_PORT_HTTPS "443"
diff --git a/src/netops.c b/src/netops.c
index 04ae824..1ef2302 100644
--- a/src/netops.c
+++ b/src/netops.c
@@ -13,7 +13,7 @@
 #include "posix.h"
 #include "buffer.h"
 #include "http_parser.h"
-#include "global.h"
+#include "runtime.h"
 
 int gitno_recv(gitno_buffer *buf)
 {
diff --git a/src/oid.c b/src/oid.c
index 7831aca..a8ad3d2 100644
--- a/src/oid.c
+++ b/src/oid.c
@@ -9,7 +9,7 @@
 
 #include "git2/oid.h"
 #include "repository.h"
-#include "global.h"
+#include "threadstate.h"
 #include <string.h>
 #include <limits.h>
 
@@ -107,7 +107,7 @@ int git_oid_pathfmt(char *str, const git_oid *oid)
 
 char *git_oid_tostr_s(const git_oid *oid)
 {
-	char *str = GIT_GLOBAL->oid_fmt;
+	char *str = GIT_THREADSTATE->oid_fmt;
 	git_oid_nfmt(str, GIT_OID_HEXSZ + 1, oid);
 	return str;
 }
diff --git a/src/runtime.c b/src/runtime.c
new file mode 100644
index 0000000..56110c4
--- /dev/null
+++ b/src/runtime.c
@@ -0,0 +1,147 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+
+#include "common.h"
+#include "runtime.h"
+
+static git_runtime_shutdown_fn shutdown_callback[32];
+static git_atomic shutdown_callback_count;
+
+static git_atomic init_count;
+
+static int init_common(git_runtime_init_fn init_fns[], size_t cnt)
+{
+	size_t i;
+	int ret;
+
+	/* Initialize subsystems that have global state */
+	for (i = 0; i < cnt; i++) {
+		if ((ret = init_fns[i]()) != 0)
+			break;
+	}
+
+	GIT_MEMORY_BARRIER;
+
+	return ret;
+}
+
+static void shutdown_common(void)
+{
+	git_runtime_shutdown_fn cb;
+	int pos;
+
+	for (pos = git_atomic_get(&shutdown_callback_count);
+	     pos > 0;
+	     pos = git_atomic_dec(&shutdown_callback_count)) {
+		cb = git__swap(shutdown_callback[pos - 1], NULL);
+
+		if (cb != NULL)
+			cb();
+	}
+}
+
+int git_runtime_shutdown_register(git_runtime_shutdown_fn callback)
+{
+	int count = git_atomic_inc(&shutdown_callback_count);
+
+	if (count > (int)ARRAY_SIZE(shutdown_callback) || count == 0) {
+		git_error_set(GIT_ERROR_INVALID,
+		              "too many shutdown callbacks registered");
+		git_atomic_dec(&shutdown_callback_count);
+		return -1;
+	}
+
+	shutdown_callback[count - 1] = callback;
+
+	return 0;
+}
+
+#if defined(GIT_THREADS) && defined(GIT_WIN32)
+
+/*
+ * On Win32, we use a spinlock to provide locking semantics.  This is
+ * lighter-weight than a proper critical section.
+ */
+static volatile LONG init_spinlock = 0;
+
+GIT_INLINE(int) init_lock(void)
+{
+	while (InterlockedCompareExchange(&init_spinlock, 1, 0)) { Sleep(0); }
+	return 0;
+}
+
+GIT_INLINE(int) init_unlock(void)
+{
+	InterlockedExchange(&init_spinlock, 0);
+	return 0;
+}
+
+#elif defined(GIT_THREADS) && defined(_POSIX_THREADS)
+
+/*
+ * On POSIX, we need to use a proper mutex for locking.  We might prefer
+ * a spinlock here, too, but there's no static initializer for a
+ * pthread_spinlock_t.
+ */
+static pthread_mutex_t init_mutex = PTHREAD_MUTEX_INITIALIZER;
+
+GIT_INLINE(int) init_lock(void)
+{
+	return pthread_mutex_lock(&init_mutex) == 0 ? 0 : -1;
+}
+
+GIT_INLINE(int) init_unlock(void)
+{
+	return pthread_mutex_unlock(&init_mutex) == 0 ? 0 : -1;
+}
+
+#elif defined(GIT_THREADS)
+# error unknown threading model
+#else
+
+# define mutex_lock() 0
+# define mutex_unlock() 0
+
+#endif
+
+int git_runtime_init(git_runtime_init_fn init_fns[], size_t cnt)
+{
+	int ret;
+
+	if (init_lock() < 0)
+		return -1;
+
+	/* Only do work on a 0 -> 1 transition of the refcount */
+	if ((ret = git_atomic_inc(&init_count)) == 1) {
+		if (init_common(init_fns, cnt) < 0)
+			ret = -1;
+	}
+
+	if (init_unlock() < 0)
+		return -1;
+
+	return ret;
+}
+
+int git_runtime_shutdown(void)
+{
+	int ret;
+
+	/* Enter the lock */
+	if (init_lock() < 0)
+		return -1;
+
+	/* Only do work on a 1 -> 0 transition of the refcount */
+	if ((ret = git_atomic_dec(&init_count)) == 0)
+		shutdown_common();
+
+	/* Exit the lock */
+	if (init_unlock() < 0)
+		return -1;
+
+	return ret;
+}
diff --git a/src/runtime.h b/src/runtime.h
new file mode 100644
index 0000000..be2e37a
--- /dev/null
+++ b/src/runtime.h
@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+#ifndef INCLUDE_runtime_h__
+#define INCLUDE_runtime_h__
+
+#include "common.h"
+
+typedef int (*git_runtime_init_fn)(void);
+typedef void (*git_runtime_shutdown_fn)(void);
+
+/**
+ * Start up a new runtime.  If this is the first time that this
+ * function is called within the context of the current library
+ * or executable, then the given `init_fns` will be invoked.  If
+ * it is not the first time, they will be ignored.
+ *
+ * The given initialization functions _may_ register shutdown
+ * handlers using `git_runtime_shutdown_register` to be notified
+ * when the runtime is shutdown.
+ *
+ * @param init_fns The list of initialization functions to call
+ * @param cnt The number of init_fns
+ * @return The number of initializations performed (including this one) or an error
+ */
+int git_runtime_init(git_runtime_init_fn init_fns[], size_t cnt);
+
+/**
+ * Shut down the runtime.  If this is the last shutdown call,
+ * such that there are no remaining `init` calls, then any
+ * shutdown hooks that have been registered will be invoked.
+ *
+ * The number of oustanding initializations will be returned.
+ * If this number is 0, then the runtime is shutdown.
+ *
+ * @return The number of outstanding initializations (after this one) or an error
+ */
+int git_runtime_shutdown(void);
+
+/**
+ * Register a shutdown handler for this runtime.  This should be done
+ * by a function invoked by `git_runtime_init` to ensure that the
+ * appropriate locks are taken.
+ *
+ * @param callback The shutdown handler callback
+ * @return 0 or an error code
+ */
+int git_runtime_shutdown_register(git_runtime_shutdown_fn callback);
+
+#endif
diff --git a/src/settings.c b/src/settings.c
deleted file mode 100644
index 69ebcb7..0000000
--- a/src/settings.c
+++ /dev/null
@@ -1,311 +0,0 @@
-/*
- * Copyright (C) the libgit2 contributors. All rights reserved.
- *
- * This file is part of libgit2, distributed under the GNU GPL v2 with
- * a Linking Exception. For full terms see the included COPYING file.
- */
-
-#include "common.h"
-
-#ifdef GIT_OPENSSL
-# include <openssl/err.h>
-#endif
-
-#ifdef GIT_MBEDTLS
-# include <mbedtls/error.h>
-#endif
-
-#include <git2.h>
-#include "alloc.h"
-#include "sysdir.h"
-#include "cache.h"
-#include "global.h"
-#include "object.h"
-#include "odb.h"
-#include "refs.h"
-#include "index.h"
-#include "transports/smart.h"
-#include "transports/http.h"
-#include "streams/openssl.h"
-#include "streams/mbedtls.h"
-
-int git_libgit2_version(int *major, int *minor, int *rev)
-{
-	*major = LIBGIT2_VER_MAJOR;
-	*minor = LIBGIT2_VER_MINOR;
-	*rev = LIBGIT2_VER_REVISION;
-
-	return 0;
-}
-
-int git_libgit2_features(void)
-{
-	return 0
-#ifdef GIT_THREADS
-		| GIT_FEATURE_THREADS
-#endif
-#ifdef GIT_HTTPS
-		| GIT_FEATURE_HTTPS
-#endif
-#if defined(GIT_SSH)
-		| GIT_FEATURE_SSH
-#endif
-#if defined(GIT_USE_NSEC)
-		| GIT_FEATURE_NSEC
-#endif
-	;
-}
-
-/* Declarations for tuneable settings */
-extern size_t git_mwindow__window_size;
-extern size_t git_mwindow__mapped_limit;
-extern size_t git_mwindow__file_limit;
-extern size_t git_indexer__max_objects;
-extern bool git_disable_pack_keep_file_checks;
-
-static int config_level_to_sysdir(int config_level)
-{
-	int val = -1;
-
-	switch (config_level) {
-	case GIT_CONFIG_LEVEL_SYSTEM:
-		val = GIT_SYSDIR_SYSTEM;
-		break;
-	case GIT_CONFIG_LEVEL_XDG:
-		val = GIT_SYSDIR_XDG;
-		break;
-	case GIT_CONFIG_LEVEL_GLOBAL:
-		val = GIT_SYSDIR_GLOBAL;
-		break;
-	case GIT_CONFIG_LEVEL_PROGRAMDATA:
-		val = GIT_SYSDIR_PROGRAMDATA;
-		break;
-	default:
-		git_error_set(
-			GIT_ERROR_INVALID, "invalid config path selector %d", config_level);
-	}
-
-	return val;
-}
-
-extern char *git__user_agent;
-extern char *git__ssl_ciphers;
-
-const char *git_libgit2__user_agent(void)
-{
-	return git__user_agent;
-}
-
-const char *git_libgit2__ssl_ciphers(void)
-{
-	return git__ssl_ciphers;
-}
-
-int git_libgit2_opts(int key, ...)
-{
-	int error = 0;
-	va_list ap;
-
-	va_start(ap, key);
-
-	switch (key) {
-	case GIT_OPT_SET_MWINDOW_SIZE:
-		git_mwindow__window_size = va_arg(ap, size_t);
-		break;
-
-	case GIT_OPT_GET_MWINDOW_SIZE:
-		*(va_arg(ap, size_t *)) = git_mwindow__window_size;
-		break;
-
-	case GIT_OPT_SET_MWINDOW_MAPPED_LIMIT:
-		git_mwindow__mapped_limit = va_arg(ap, size_t);
-		break;
-
-	case GIT_OPT_GET_MWINDOW_MAPPED_LIMIT:
-		*(va_arg(ap, size_t *)) = git_mwindow__mapped_limit;
-		break;
-
-	case GIT_OPT_SET_MWINDOW_FILE_LIMIT:
-		git_mwindow__file_limit = va_arg(ap, size_t);
-		break;
-
-	case GIT_OPT_GET_MWINDOW_FILE_LIMIT:
-		*(va_arg(ap, size_t *)) = git_mwindow__file_limit;
-		break;
-
-	case GIT_OPT_GET_SEARCH_PATH:
-		if ((error = config_level_to_sysdir(va_arg(ap, int))) >= 0) {
-			git_buf *out = va_arg(ap, git_buf *);
-			const git_buf *tmp;
-
-			git_buf_sanitize(out);
-			if ((error = git_sysdir_get(&tmp, error)) < 0)
-				break;
-
-			error = git_buf_sets(out, tmp->ptr);
-		}
-		break;
-
-	case GIT_OPT_SET_SEARCH_PATH:
-		if ((error = config_level_to_sysdir(va_arg(ap, int))) >= 0)
-			error = git_sysdir_set(error, va_arg(ap, const char *));
-		break;
-
-	case GIT_OPT_SET_CACHE_OBJECT_LIMIT:
-		{
-			git_object_t type = (git_object_t)va_arg(ap, int);
-			size_t size = va_arg(ap, size_t);
-			error = git_cache_set_max_object_size(type, size);
-			break;
-		}
-
-	case GIT_OPT_SET_CACHE_MAX_SIZE:
-		git_cache__max_storage = va_arg(ap, ssize_t);
-		break;
-
-	case GIT_OPT_ENABLE_CACHING:
-		git_cache__enabled = (va_arg(ap, int) != 0);
-		break;
-
-	case GIT_OPT_GET_CACHED_MEMORY:
-		*(va_arg(ap, ssize_t *)) = git_cache__current_storage.val;
-		*(va_arg(ap, ssize_t *)) = git_cache__max_storage;
-		break;
-
-	case GIT_OPT_GET_TEMPLATE_PATH:
-		{
-			git_buf *out = va_arg(ap, git_buf *);
-			const git_buf *tmp;
-
-			git_buf_sanitize(out);
-			if ((error = git_sysdir_get(&tmp, GIT_SYSDIR_TEMPLATE)) < 0)
-				break;
-
-			error = git_buf_sets(out, tmp->ptr);
-		}
-		break;
-
-	case GIT_OPT_SET_TEMPLATE_PATH:
-		error = git_sysdir_set(GIT_SYSDIR_TEMPLATE, va_arg(ap, const char *));
-		break;
-
-	case GIT_OPT_SET_SSL_CERT_LOCATIONS:
-#ifdef GIT_OPENSSL
-		{
-			const char *file = va_arg(ap, const char *);
-			const char *path = va_arg(ap, const char *);
-			error = git_openssl__set_cert_location(file, path);
-		}
-#elif defined(GIT_MBEDTLS)
-		{
-			const char *file = va_arg(ap, const char *);
-			const char *path = va_arg(ap, const char *);
-			if (file)
-				error = git_mbedtls__set_cert_location(file, 0);
-			if (error && path)
-				error = git_mbedtls__set_cert_location(path, 1);
-		}
-#else
-		git_error_set(GIT_ERROR_SSL, "TLS backend doesn't support certificate locations");
-		error = -1;
-#endif
-		break;
-	case GIT_OPT_SET_USER_AGENT:
-		git__free(git__user_agent);
-		git__user_agent = git__strdup(va_arg(ap, const char *));
-		if (!git__user_agent) {
-			git_error_set_oom();
-			error = -1;
-		}
-
-		break;
-
-	case GIT_OPT_ENABLE_STRICT_OBJECT_CREATION:
-		git_object__strict_input_validation = (va_arg(ap, int) != 0);
-		break;
-
-	case GIT_OPT_ENABLE_STRICT_SYMBOLIC_REF_CREATION:
-		git_reference__enable_symbolic_ref_target_validation = (va_arg(ap, int) != 0);
-		break;
-
-	case GIT_OPT_SET_SSL_CIPHERS:
-#if (GIT_OPENSSL || GIT_MBEDTLS)
-		{
-			git__free(git__ssl_ciphers);
-			git__ssl_ciphers = git__strdup(va_arg(ap, const char *));
-			if (!git__ssl_ciphers) {
-				git_error_set_oom();
-				error = -1;
-			}
-		}
-#else
-		git_error_set(GIT_ERROR_SSL, "TLS backend doesn't support custom ciphers");
-		error = -1;
-#endif
-		break;
-
-	case GIT_OPT_GET_USER_AGENT:
-		{
-			git_buf *out = va_arg(ap, git_buf *);
-			git_buf_sanitize(out);
-			error = git_buf_sets(out, git__user_agent);
-		}
-		break;
-
-	case GIT_OPT_ENABLE_OFS_DELTA:
-		git_smart__ofs_delta_enabled = (va_arg(ap, int) != 0);
-		break;
-
-	case GIT_OPT_ENABLE_FSYNC_GITDIR:
-		git_repository__fsync_gitdir = (va_arg(ap, int) != 0);
-		break;
-
-	case GIT_OPT_GET_WINDOWS_SHAREMODE:
-#ifdef GIT_WIN32
-		*(va_arg(ap, unsigned long *)) = git_win32__createfile_sharemode;
-#endif
-		break;
-
-	case GIT_OPT_SET_WINDOWS_SHAREMODE:
-#ifdef GIT_WIN32
-		git_win32__createfile_sharemode = va_arg(ap, unsigned long);
-#endif
-		break;
-
-	case GIT_OPT_ENABLE_STRICT_HASH_VERIFICATION:
-		git_odb__strict_hash_verification = (va_arg(ap, int) != 0);
-		break;
-
-	case GIT_OPT_SET_ALLOCATOR:
-		error = git_allocator_setup(va_arg(ap, git_allocator *));
-		break;
-
-	case GIT_OPT_ENABLE_UNSAVED_INDEX_SAFETY:
-		git_index__enforce_unsaved_safety = (va_arg(ap, int) != 0);
-		break;
-
-	case GIT_OPT_SET_PACK_MAX_OBJECTS:
-		git_indexer__max_objects = va_arg(ap, size_t);
-		break;
-
-	case GIT_OPT_GET_PACK_MAX_OBJECTS:
-		*(va_arg(ap, size_t *)) = git_indexer__max_objects;
-		break;
-
-	case GIT_OPT_DISABLE_PACK_KEEP_FILE_CHECKS:
-		git_disable_pack_keep_file_checks = (va_arg(ap, int) != 0);
-		break;
-
-	case GIT_OPT_ENABLE_HTTP_EXPECT_CONTINUE:
-		git_http__expect_continue = (va_arg(ap, int) != 0);
-		break;
-
-	default:
-		git_error_set(GIT_ERROR_INVALID, "invalid option key");
-		error = -1;
-	}
-
-	va_end(ap);
-
-	return error;
-}
diff --git a/src/settings.h b/src/settings.h
new file mode 100644
index 0000000..dc42ce9
--- /dev/null
+++ b/src/settings.h
@@ -0,0 +1,11 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+
+extern int git_settings_global_init(void);
+
+extern const char *git_libgit2__user_agent(void);
+extern const char *git_libgit2__ssl_ciphers(void);
diff --git a/src/streams/mbedtls.c b/src/streams/mbedtls.c
index cbe2f68..00daa55 100644
--- a/src/streams/mbedtls.c
+++ b/src/streams/mbedtls.c
@@ -11,7 +11,7 @@
 
 #include <ctype.h>
 
-#include "global.h"
+#include "runtime.h"
 #include "stream.h"
 #include "streams/socket.h"
 #include "netops.h"
@@ -152,9 +152,7 @@ int git_mbedtls_stream_global_init(void)
 	if (!loaded && crtpath != NULL && stat(crtpath, &statbuf) == 0 && S_ISDIR(statbuf.st_mode))
 		loaded = (git_mbedtls__set_cert_location(crtpath, 1) == 0);
 
-	git__on_shutdown(shutdown_ssl);
-
-	return 0;
+	return git_runtime_shutdown_register(shutdown_ssl);
 
 cleanup:
 	mbedtls_ctr_drbg_free(ctr_drbg);
diff --git a/src/streams/openssl.c b/src/streams/openssl.c
index 6a490d1..0a0c2c5 100644
--- a/src/streams/openssl.c
+++ b/src/streams/openssl.c
@@ -11,7 +11,8 @@
 
 #include <ctype.h>
 
-#include "global.h"
+#include "runtime.h"
+#include "settings.h"
 #include "posix.h"
 #include "stream.h"
 #include "streams/socket.h"
@@ -285,9 +286,7 @@ int git_openssl_stream_global_init(void)
 	if (init_bio_method() < 0)
 		goto error;
 
-	git__on_shutdown(shutdown_ssl);
-
-	return 0;
+	return git_runtime_shutdown_register(shutdown_ssl);
 
 error:
 	git_error_set(GIT_ERROR_NET, "could not initialize openssl: %s",
@@ -324,8 +323,8 @@ int git_openssl_set_locking(void)
 	}
 
 	CRYPTO_set_locking_callback(openssl_locking_function);
-	git__on_shutdown(shutdown_ssl_locking);
-	return 0;
+	return git_runtime_shutdown_register(shutdown_ssl_locking);
+
 #elif !defined(OPENSSL_LEGACY_API)
 	return 0;
 #else
diff --git a/src/streams/registry.c b/src/streams/registry.c
index 2844312..b3bf17a 100644
--- a/src/streams/registry.c
+++ b/src/streams/registry.c
@@ -9,7 +9,7 @@
 
 #include "streams/registry.h"
 
-#include "global.h"
+#include "runtime.h"
 #include "streams/tls.h"
 #include "streams/mbedtls.h"
 #include "streams/openssl.h"
@@ -33,8 +33,7 @@ int git_stream_registry_global_init(void)
 	if (git_rwlock_init(&stream_registry.lock) < 0)
 		return -1;
 
-	git__on_shutdown(shutdown_stream_registry);
-	return 0;
+	return git_runtime_shutdown_register(shutdown_stream_registry);
 }
 
 GIT_INLINE(void) stream_registration_cpy(
diff --git a/src/streams/tls.c b/src/streams/tls.c
index 6a25171..255a4a0 100644
--- a/src/streams/tls.c
+++ b/src/streams/tls.c
@@ -8,7 +8,6 @@
 #include "git2/errors.h"
 
 #include "common.h"
-#include "global.h"
 #include "streams/registry.h"
 #include "streams/tls.h"
 #include "streams/mbedtls.h"
diff --git a/src/sysdir.c b/src/sysdir.c
index 6dc78c8..401b4a5 100644
--- a/src/sysdir.c
+++ b/src/sysdir.c
@@ -7,7 +7,7 @@
 
 #include "sysdir.h"
 
-#include "global.h"
+#include "runtime.h"
 #include "buffer.h"
 #include "path.h"
 #include <ctype.h>
@@ -189,9 +189,7 @@ int git_sysdir_global_init(void)
 	for (i = 0; !error && i < ARRAY_SIZE(git_sysdir__dirs); i++)
 		error = git_sysdir__dirs[i].guess(&git_sysdir__dirs[i].buf);
 
-	git__on_shutdown(git_sysdir_global_shutdown);
-
-	return error;
+	return git_runtime_shutdown_register(git_sysdir_global_shutdown);
 }
 
 static int git_sysdir_check_selector(git_sysdir_t which)
diff --git a/src/thread-utils.h b/src/thread-utils.h
index 3311672..b4e44b4 100644
--- a/src/thread-utils.h
+++ b/src/thread-utils.h
@@ -235,6 +235,8 @@ GIT_INLINE(int64_t) git_atomic64_get(git_atomic64 *a)
 
 #else
 
+GIT_INLINE(int) git_threads_global_init(void) { return 0; }
+
 #define git_thread unsigned int
 #define git_thread_create(thread, start_routine, arg) 0
 #define git_thread_join(id, status) (void)0
diff --git a/src/threadstate.c b/src/threadstate.c
new file mode 100644
index 0000000..8e17124
--- /dev/null
+++ b/src/threadstate.c
@@ -0,0 +1,155 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+
+#include "threadstate.h"
+#include "runtime.h"
+
+static void threadstate_dispose(git_threadstate *threadstate);
+
+/**
+ * Handle the thread-local state
+ *
+ * `git_threadstate_global_init` will be called as part
+ * of `git_libgit2_init` (which itself must be called
+ * before calling any other function in the library).
+ *
+ * This function allocates a TLS index (using pthreads
+ * or fiber-local storage in Win32) to store the per-
+ * thread state.
+ *
+ * Any internal method that requires thread-local state
+ * will then call `git_threadstate_get()` which returns a
+ * pointer to the thread-local state structure; this
+ * structure is lazily allocated on each thread.
+ *
+ * This mechanism will register a shutdown handler
+ * (`git_threadstate_global_shutdown`) which will free the
+ * TLS index.  This shutdown handler will be called by
+ * `git_libgit2_shutdown`.
+ *
+ * If libgit2 is built without threading support, the
+ * `git_threadstate_get()` call returns a pointer to a single,
+ * statically allocated global state. The `git_thread_`
+ * functions are not available in that case.
+ */
+
+#if defined(GIT_THREADS) && defined(GIT_WIN32)
+
+static DWORD fls_index;
+
+static void git_threadstate_global_shutdown(void)
+{
+	FlsFree(fls_index);
+}
+
+static void WINAPI fls_free(void *threadstate)
+{
+	threadstate_dispose(threadstate);
+	git__free(threadstate);
+}
+
+int git_threadstate_global_init(void)
+{
+	if ((fls_index = FlsAlloc(fls_free)) == FLS_OUT_OF_INDEXES)
+		return -1;
+
+	return git_runtime_shutdown_register(git_threadstate_global_shutdown);
+}
+
+git_threadstate *git_threadstate_get(void)
+{
+	git_threadstate *threadstate;
+
+	if ((threadstate = FlsGetValue(fls_index)) != NULL)
+		return threadstate;
+
+	if ((threadstate = git__calloc(1, sizeof(git_threadstate))) == NULL ||
+	    git_buf_init(&threadstate->error_buf, 0) < 0)
+		return NULL;
+
+	FlsSetValue(fls_index, threadstate);
+	return threadstate;
+}
+
+#elif defined(GIT_THREADS) && defined(_POSIX_THREADS)
+
+static pthread_key_t tls_key;
+
+static void git_threadstate_global_shutdown(void)
+{
+	git_threadstate *threadstate;
+
+	threadstate = pthread_getspecific(tls_key);
+	pthread_setspecific(tls_key, NULL);
+
+	threadstate_dispose(threadstate);
+	git__free(threadstate);
+
+	pthread_key_delete(tls_key);
+}
+
+static void tls_free(void *threadstate)
+{
+	threadstate_dispose(threadstate);
+	git__free(threadstate);
+}
+
+int git_threadstate_global_init(void)
+{
+	if (pthread_key_create(&tls_key, &tls_free) != 0)
+		return -1;
+
+	return git_runtime_shutdown_register(git_threadstate_global_shutdown);
+}
+
+git_threadstate *git_threadstate_get(void)
+{
+	git_threadstate *threadstate;
+
+	if ((threadstate = pthread_getspecific(tls_key)) != NULL)
+		return threadstate;
+
+	if ((threadstate = git__calloc(1, sizeof(git_threadstate))) == NULL ||
+	    git_buf_init(&threadstate->error_buf, 0) < 0)
+		return NULL;
+
+	pthread_setspecific(tls_key, threadstate);
+	return threadstate;
+}
+
+#elif defined(GIT_THREADS)
+# error unknown threading model
+#else
+
+static git_threadstate threadstate;
+
+static void git_threadstate_global_shutdown(void)
+{
+	threadstate_dispose(&threadstate);
+	memset(&threadstate, 0, sizeof(git_threadstate));
+}
+
+int git_threadstate_global_init(void)
+{
+	return git_runtime_shutdown_register(git_tlsdata_global_shutdown);
+}
+
+git_threadstate *git_threadstate_get(void)
+{
+	return &threadstate;
+}
+
+#endif
+
+static void threadstate_dispose(git_threadstate *threadstate)
+{
+	if (!threadstate)
+		return;
+
+	git__free(threadstate->error_t.message);
+	threadstate->error_t.message = NULL;
+}
diff --git a/src/threadstate.h b/src/threadstate.h
new file mode 100644
index 0000000..51810a9
--- /dev/null
+++ b/src/threadstate.h
@@ -0,0 +1,24 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+#ifndef INCLUDE_threadstate_h__
+#define INCLUDE_threadstate_h__
+
+#include "common.h"
+
+typedef struct {
+	git_error *last_error;
+	git_error error_t;
+	git_buf error_buf;
+	char oid_fmt[GIT_OID_HEXSZ+1];
+} git_threadstate;
+
+extern int git_threadstate_global_init(void);
+extern git_threadstate *git_threadstate_get(void);
+
+#define GIT_THREADSTATE (git_threadstate_get())
+
+#endif
diff --git a/src/trace.c b/src/trace.c
index ec6a90a..3acb643 100644
--- a/src/trace.c
+++ b/src/trace.c
@@ -8,7 +8,7 @@
 #include "trace.h"
 
 #include "buffer.h"
-#include "global.h"
+#include "runtime.h"
 #include "git2/trace.h"
 
 #ifdef GIT_TRACE
diff --git a/src/transports/http.c b/src/transports/http.c
index 66731b0..fb1740c 100644
--- a/src/transports/http.c
+++ b/src/transports/http.c
@@ -14,7 +14,6 @@
 #include "buffer.h"
 #include "net.h"
 #include "netops.h"
-#include "global.h"
 #include "remote.h"
 #include "git2/sys/credential.h"
 #include "smart.h"
diff --git a/src/transports/http.h b/src/transports/http.h
index c02109c..5c360b8 100644
--- a/src/transports/http.h
+++ b/src/transports/http.h
@@ -9,6 +9,7 @@
 #define INCLUDE_transports_http_h__
 
 #include "buffer.h"
+#include "settings.h"
 #include "httpclient.h"
 
 #define GIT_HTTP_REPLAY_MAX 15
diff --git a/src/transports/httpclient.c b/src/transports/httpclient.c
index ee936c8..6ec22f8 100644
--- a/src/transports/httpclient.c
+++ b/src/transports/httpclient.c
@@ -10,7 +10,6 @@
 #include "http_parser.h"
 #include "vector.h"
 #include "trace.h"
-#include "global.h"
 #include "httpclient.h"
 #include "http.h"
 #include "auth.h"
diff --git a/src/transports/ssh.c b/src/transports/ssh.c
index 68b3cbe..f4ed05b 100644
--- a/src/transports/ssh.c
+++ b/src/transports/ssh.c
@@ -11,7 +11,7 @@
 #include <libssh2.h>
 #endif
 
-#include "global.h"
+#include "runtime.h"
 #include "git2.h"
 #include "buffer.h"
 #include "net.h"
@@ -934,8 +934,7 @@ int git_transport_ssh_global_init(void)
 		return -1;
 	}
 
-	git__on_shutdown(shutdown_ssh);
-	return 0;
+	return git_runtime_shutdown_register(shutdown_ssh);
 
 #else
 
diff --git a/src/transports/winhttp.c b/src/transports/winhttp.c
index f9736cd..2a1f6f2 100644
--- a/src/transports/winhttp.c
+++ b/src/transports/winhttp.c
@@ -17,7 +17,6 @@
 #include "smart.h"
 #include "remote.h"
 #include "repository.h"
-#include "global.h"
 #include "http.h"
 #include "git2/sys/credential.h"
 
diff --git a/src/unix/pthread.h b/src/unix/pthread.h
index 233561b..55f4ae2 100644
--- a/src/unix/pthread.h
+++ b/src/unix/pthread.h
@@ -12,7 +12,8 @@ typedef struct {
 	pthread_t thread;
 } git_thread;
 
-#define git_threads_init() (void)0
+GIT_INLINE(int) git_threads_global_init(void) { return 0; }
+
 #define git_thread_create(git_thread_ptr, start_routine, arg) \
 	pthread_create(&(git_thread_ptr)->thread, NULL, start_routine, arg)
 #define git_thread_join(git_thread_ptr, status) \
diff --git a/src/win32/posix_w32.c b/src/win32/posix_w32.c
index cacf986..5a5e921 100644
--- a/src/win32/posix_w32.c
+++ b/src/win32/posix_w32.c
@@ -14,7 +14,6 @@
 #include "utf-conv.h"
 #include "repository.h"
 #include "reparse.h"
-#include "global.h"
 #include "buffer.h"
 #include <errno.h>
 #include <io.h>
diff --git a/src/win32/thread.c b/src/win32/thread.c
index 42dba7f..51b005b 100644
--- a/src/win32/thread.c
+++ b/src/win32/thread.c
@@ -6,8 +6,7 @@
  */
 
 #include "thread.h"
-
-#include "../global.h"
+#include "runtime.h"
 
 #define CLEAN_THREAD_EXIT 0x6F012842
 
@@ -19,6 +18,8 @@ static win32_srwlock_fn win32_srwlock_release_shared;
 static win32_srwlock_fn win32_srwlock_acquire_exclusive;
 static win32_srwlock_fn win32_srwlock_release_exclusive;
 
+static DWORD fls_index;
+
 /* The thread procedure stub used to invoke the caller's procedure
  * and capture the return value for later collection. Windows will
  * only hold a DWORD, but we need to be able to store an entire
@@ -28,14 +29,19 @@ static DWORD WINAPI git_win32__threadproc(LPVOID lpParameter)
 	git_thread *thread = lpParameter;
 
 	/* Set the current thread for `git_thread_exit` */
-	GIT_GLOBAL->current_thread = thread;
+	FlsSetValue(fls_index, thread);
 
 	thread->result = thread->proc(thread->param);
 
 	return CLEAN_THREAD_EXIT;
 }
 
-int git_threads_init(void)
+static void git_threads_global_shutdown(void)
+{
+	FlsFree(fls_index);
+}
+
+int git_threads_global_init(void)
 {
 	HMODULE hModule = GetModuleHandleW(L"kernel32");
 
@@ -52,7 +58,10 @@ int git_threads_init(void)
 			GetProcAddress(hModule, "ReleaseSRWLockExclusive");
 	}
 
-	return 0;
+	if ((fls_index = FlsAlloc(NULL)) == FLS_OUT_OF_INDEXES)
+		return -1;
+
+	return git_runtime_shutdown_register(git_threads_global_shutdown);
 }
 
 int git_thread_create(
@@ -99,8 +108,11 @@ int git_thread_join(
 
 void git_thread_exit(void *value)
 {
-	assert(GIT_GLOBAL->current_thread);
-	GIT_GLOBAL->current_thread->result = value;
+	git_thread *thread = FlsGetValue(fls_index);
+
+	if (thread)
+		thread->result = value;
+
 	ExitThread(CLEAN_THREAD_EXIT);
 }
 
diff --git a/src/win32/thread.h b/src/win32/thread.h
index 41cbf01..8305036 100644
--- a/src/win32/thread.h
+++ b/src/win32/thread.h
@@ -35,7 +35,7 @@ typedef struct {
 	} native;
 } git_rwlock;
 
-int git_threads_init(void);
+int git_threads_global_init(void);
 
 int git_thread_create(git_thread *GIT_RESTRICT,
 	void *(*) (void *),
diff --git a/tests/core/useragent.c b/tests/core/useragent.c
index c6c5220..2ce935b 100644
--- a/tests/core/useragent.c
+++ b/tests/core/useragent.c
@@ -1,5 +1,5 @@
 #include "clar_libgit2.h"
-#include "global.h"
+#include "settings.h"
 
 void test_core_useragent__get(void)
 {
diff --git a/tests/pack/filelimit.c b/tests/pack/filelimit.c
index 044679f..b39ab73 100644
--- a/tests/pack/filelimit.c
+++ b/tests/pack/filelimit.c
@@ -1,6 +1,5 @@
 #include "clar_libgit2.h"
 #include "mwindow.h"
-#include "global.h"
 
 #include <git2.h>
 #include "git2/sys/commit.h"
diff --git a/tests/threads/basic.c b/tests/threads/basic.c
index ed4fd2f..2d7ddc2 100644
--- a/tests/threads/basic.c
+++ b/tests/threads/basic.c
@@ -54,6 +54,12 @@ static void *return_normally(void *param)
 {
 	return param;
 }
+
+static void *exit_abruptly(void *param)
+{
+	git_thread_exit(param);
+	return NULL;
+}
 #endif
 
 void test_threads_basic__exit(void)
@@ -70,7 +76,7 @@ void test_threads_basic__exit(void)
 	cl_assert_equal_sz(424242, (size_t)result);
 
 	/* Ensure that the return value of `git_thread_exit` is returned. */
-	cl_git_pass(git_thread_create(&thread, return_normally, (void *)232323));
+	cl_git_pass(git_thread_create(&thread, exit_abruptly, (void *)232323));
 	cl_git_pass(git_thread_join(&thread, &result));
 	cl_assert_equal_sz(232323, (size_t)result);
 #endif