/*
* 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 "global.h"
#include "hash.h"
#include "sysdir.h"
#include "git2/threads.h"
#include "thread-utils.h"
git_mutex git__mwindow_mutex;
#define MAX_SHUTDOWN_CB 8
git_global_shutdown_fn git__shutdown_callbacks[MAX_SHUTDOWN_CB];
git_atomic git__n_shutdown_callbacks;
void git__on_shutdown(git_global_shutdown_fn callback)
{
int count = git_atomic_inc(&git__n_shutdown_callbacks);
assert(count <= MAX_SHUTDOWN_CB);
git__shutdown_callbacks[count - 1] = callback;
}
static void git__shutdown(void)
{
int pos;
while ((pos = git_atomic_dec(&git__n_shutdown_callbacks)) >= 0) {
if (git__shutdown_callbacks[pos])
git__shutdown_callbacks[pos]();
}
}
/**
* Handle the global state with TLS
*
* If libgit2 is built with GIT_THREADS enabled,
* the `git_threads_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_threads_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_threads_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_threads_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 _tls_index;
static DWORD _mutex = 0;
static DWORD _n_inits = 0;
static int synchronized_threads_init()
{
int error;
_tls_index = TlsAlloc();
if (git_mutex_init(&git__mwindow_mutex))
return -1;
/* Initialize any other subsystems that have global state */
if ((error = git_hash_global_init()) >= 0)
error = git_sysdir_global_init();
win32_pthread_initialize();
return error;
}
int git_threads_init(void)
{
int error = 0;
/* Enter the lock */
while (InterlockedCompareExchange(&_mutex, 1, 0)) { Sleep(0); }
/* Only do work on a 0 -> 1 transition of the refcount */
if (1 == ++_n_inits)
error = synchronized_threads_init();
/* Exit the lock */
InterlockedExchange(&_mutex, 0);
return error;
}
static void synchronized_threads_shutdown()
{
/* Shut down any subsystems that have global state */
git__shutdown();
TlsFree(_tls_index);
git_mutex_free(&git__mwindow_mutex);
}
void git_threads_shutdown(void)
{
/* Enter the lock */
while (InterlockedCompareExchange(&_mutex, 1, 0)) { Sleep(0); }
/* Only do work on a 1 -> 0 transition of the refcount */
if (0 == --_n_inits)
synchronized_threads_shutdown();
/* Exit the lock */
InterlockedExchange(&_mutex, 0);
}
git_global_st *git__global_state(void)
{
void *ptr;
assert(_n_inits);
if ((ptr = TlsGetValue(_tls_index)) != NULL)
return ptr;
ptr = git__malloc(sizeof(git_global_st));
if (!ptr)
return NULL;
memset(ptr, 0x0, sizeof(git_global_st));
TlsSetValue(_tls_index, ptr);
return ptr;
}
#elif defined(GIT_THREADS) && defined(_POSIX_THREADS)
static pthread_key_t _tls_key;
static pthread_once_t _once_init = PTHREAD_ONCE_INIT;
static git_atomic git__n_inits;
int init_error = 0;
static void cb__free_status(void *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);
/* Initialize any other subsystems that have global state */
if ((init_error = git_hash_global_init()) >= 0)
init_error = git_sysdir_global_init();
GIT_MEMORY_BARRIER;
}
int git_threads_init(void)
{
pthread_once(&_once_init, init_once);
git_atomic_inc(&git__n_inits);
return init_error;
}
void git_threads_shutdown(void)
{
void *ptr = NULL;
pthread_once_t new_once = PTHREAD_ONCE_INIT;
if (git_atomic_dec(&git__n_inits) > 0) return;
/* Shut down any subsystems that have global state */
git__shutdown();
ptr = pthread_getspecific(_tls_key);
pthread_setspecific(_tls_key, NULL);
git__free(ptr);
pthread_key_delete(_tls_key);
git_mutex_free(&git__mwindow_mutex);
_once_init = new_once;
}
git_global_st *git__global_state(void)
{
void *ptr;
assert(git__n_inits.val);
if ((ptr = pthread_getspecific(_tls_key)) != NULL)
return ptr;
ptr = git__malloc(sizeof(git_global_st));
if (!ptr)
return NULL;
memset(ptr, 0x0, sizeof(git_global_st));
pthread_setspecific(_tls_key, ptr);
return ptr;
}
#else
static git_global_st __state;
int git_threads_init(void)
{
/* noop */
return 0;
}
void git_threads_shutdown(void)
{
/* Shut down any subsystems that have global state */
git__shutdown();
}
git_global_st *git__global_state(void)
{
return &__state;
}
#endif /* GIT_THREADS */
