thodg/libgit2/src/runtime.c

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• Hash : 6c51014d
  Author :
  Date : 2020-07-11T14:24:17
  

  libgit2: provide init_count of the library A function to provide the initialization count of the library; this is subject to race conditions but is useful for a naive determination as to whether the library has been initialized or not.

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• src/runtime.c

• /*
   * 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_atomic32 shutdown_callback_count;
  
  static git_atomic32 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_atomic32_get(&shutdown_callback_count);
  	     pos > 0;
  	     pos = git_atomic32_dec(&shutdown_callback_count)) {
  		cb = git_atomic_swap(shutdown_callback[pos - 1], NULL);
  
  		if (cb != NULL)
  			cb();
  	}
  }
  
  int git_runtime_shutdown_register(git_runtime_shutdown_fn callback)
  {
  	int count = git_atomic32_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_atomic32_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 init_lock() git__noop()
  # define init_unlock() git__noop()
  
  #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_atomic32_inc(&init_count)) == 1) {
  		if (init_common(init_fns, cnt) < 0)
  			ret = -1;
  	}
  
  	if (init_unlock() < 0)
  		return -1;
  
  	return ret;
  }
  
  int git_runtime_init_count(void)
  {
  	int ret;
  
  	if (init_lock() < 0)
  		return -1;
  
  	ret = git_atomic32_get(&init_count);
  
  	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_atomic32_dec(&init_count)) == 0)
  		shutdown_common();
  
  	/* Exit the lock */
  	if (init_unlock() < 0)
  		return -1;
  
  	return ret;
  }
  

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