thodg/libgit2/src/global.c

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• Hash : 1a42dd17
  Author :
  Date : 2013-05-31T14:13:11
  

  Mutex init can fail It is obviously quite a serious problem if this happens, but mutex initialization can fail and we should detect it. It's a bit like a memory allocation failure, in that you're probably pretty screwed if this occurs, but at least we'll catch it.

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• src/global.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 "global.h"
  #include "hash.h"
  #include "fileops.h"
  #include "git2/threads.h"
  #include "thread-utils.h"
  
  
  git_mutex git__mwindow_mutex;
  
  /**
   * 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 int _tls_init = 0;
  
  int git_threads_init(void)
  {
  	int error;
  
  	if (_tls_init)
  		return 0;
  
  	_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)
  		_tls_init = 1;
  
  	if (error == 0)
  		_tls_init = 1;
  
  	GIT_MEMORY_BARRIER;
  
  	return error;
  }
  
  void git_threads_shutdown(void)
  {
  	TlsFree(_tls_index);
  	_tls_init = 0;
  	git_mutex_free(&git__mwindow_mutex);
  
  	/* Shut down any subsystems that have global state */
  	git_hash_global_shutdown();
  	git_futils_dirs_free();
  }
  
  git_global_st *git__global_state(void)
  {
  	void *ptr;
  
  	assert(_tls_init);
  
  	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 int _tls_init = 0;
  
  static void cb__free_status(void *st)
  {
  	git__free(st);
  }
  
  int git_threads_init(void)
  {
  	int error = 0;
  
  	if (_tls_init)
  		return 0;
  
  	if (git_mutex_init(&git__mwindow_mutex))
  		return -1;
  	pthread_key_create(&_tls_key, &cb__free_status);
  
  	/* Initialize any other subsystems that have global state */
  	if ((error = git_hash_global_init()) >= 0)
  		_tls_init = 1;
  
  	GIT_MEMORY_BARRIER;
  
  	return error;
  }
  
  void git_threads_shutdown(void)
  {
  	if (_tls_init) {
  		void *ptr = pthread_getspecific(_tls_key);
  		pthread_setspecific(_tls_key, NULL);
  		git__free(ptr);
  	}
  
  	pthread_key_delete(_tls_key);
  	_tls_init = 0;
  	git_mutex_free(&git__mwindow_mutex);
  
  	/* Shut down any subsystems that have global state */
  	git_hash_global_shutdown();
  	git_futils_dirs_free();
  }
  
  git_global_st *git__global_state(void)
  {
  	void *ptr;
  
  	assert(_tls_init);
  
  	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_hash_global_shutdown();
  	git_futils_dirs_free();
  }
  
  git_global_st *git__global_state(void)
  {
  	return &__state;
  }
  
  #endif /* GIT_THREADS */
  

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