GMutex / GCond

os posted @ 2013年9月23日 14:59 in Glib , 3212 阅读

下面两个函数:
void g_cond_signal (GCond *cond);
void g_cond_wait (GCond *cond, GMutex *mutex);
 

用于进行线程同步。
mutex 是“mutual exclusion”(互斥)的英文缩写,用来保证线程对于共享数据的独占访问。

 

GMutex *mutex; // 互斥变量

GCond *cond; //等待条件

 

CRITICAL_SECTION 属于轻量级的线程同步对象,相对于mutex来说,它的效率会高很多。

mutex可以用于进程之间的同步,CRITICAL_SECTION只在同一个进程有效。

 

同一进程可以包括多个线程,这些线程共享相同的内存空间,而进程都有各自独立的内存空间,进程之间通信需要专门的机制,这无疑增加了内核的开销,降低了系 统性能。线程带来的开销很小,内核无需单独复制进程的内存空间或文件描述符等,这就大量地节省了CPU时间,使得创建线程比进程的速度快数十倍。另外,多 线程程序作为一种多任务、并发的工作方式,还有以下的优点:1)提高应用程序响应时间;2)使多CPU系统更加有效;3)改善程序结构。
首先我们理清一下Pthread和Gthread的区别。Pthread即POSIX thread,Posix线程是一个POSIX标准线程,该标准定义内部API创建和操纵线程。Gthread调用的是Glib库中的线程部分;GLib是GTK+和GNOME工程的基础底层核心程序库,是一个综合用途的实用的轻量级的C程序库。 本软件是带有界面的,并且是GTK+界面,因此,Gthread是最好的选择。
引入Gthread线程的文件在编译时要加入参数`pkg-config --cflags --libs gthread-2.0`。
(1)gboolean g_thread_supported();/*测试是否支持多线程*/
(2)void g_thread_init (GThreadFunctions *vtable);/*初始化多线程支持*/
(3)void gdk_threads_init (void);/*初始化GDK多线程支持*/
(4)void gdk_threads_enter (void);/*进入多线程互斥区域*/
(5)void gdk_threads_leave (void);/*退出多线程互斥区域*/
(6)GThread * g_thread_create (GThreadFunc func, gpointer data, gboolean joinable, GError **error);
这是创建线程函数,func是线程执行的外部函数,data是传给该外部函数的参数,joinable标志线程是否可分离,error是出错代码返回地址。
(7)void g_thread_exit (gpointer retval);/*线程退出,retval为返回状态值*/
(8)GMutex *g_mutex_new ();/*返回一个新的互斥锁*/
(9) void g_mutex_lock(GMutex *mutex);/*上锁*/
(10)void g_mutex_unlock (GMutex *mutex);/*解锁*/
(11)GCond* g_cond_new ();/*返回一个新的信号量*/
(12)void g_cond_signal (GCond *cond);/*释放信号量cond*/
(13)void g_cond_wait(GCond *cond, GMutex *mutex);/*等待信号量cond*/

 

#define g_mutex_new()            G_THREAD_UF (mutex_new,      ())
#define G_THREAD_UF(op, arglist)					\
    (*g_thread_functions_for_glib_use . op) arglist

#define g_mutex_new()            (*g_thread_functions_for_glib_use.mutex_new())

 

#define g_cond_new()             G_THREAD_UF (cond_new,       ())

#define g_cond_new()             (*g_thread_functions_for_glib_use.cond_new())

 

typedef gpointer (*GThreadFunc) (gpointer data);

typedef enum
{
  G_THREAD_PRIORITY_LOW,
  G_THREAD_PRIORITY_NORMAL,
  G_THREAD_PRIORITY_HIGH,
  G_THREAD_PRIORITY_URGENT
} GThreadPriority;

typedef struct _GThread         GThread;
struct  _GThread
{
  /*< private >*/
  GThreadFunc func;
  gpointer data;
  gboolean joinable;
  GThreadPriority priority;
};

typedef struct _GMutex          GMutex;
typedef struct _GCond           GCond;
typedef struct _GPrivate        GPrivate;
typedef struct _GStaticPrivate  GStaticPrivate;

typedef struct _GThreadFunctions GThreadFunctions;
struct _GThreadFunctions
{
  GMutex*  (*mutex_new)           (void);
  void     (*mutex_lock)          (GMutex               *mutex);
  gboolean (*mutex_trylock)       (GMutex               *mutex);
  void     (*mutex_unlock)        (GMutex               *mutex);
  void     (*mutex_free)          (GMutex               *mutex);
  GCond*   (*cond_new)            (void);
  void     (*cond_signal)         (GCond                *cond);
  void     (*cond_broadcast)      (GCond                *cond);
  void     (*cond_wait)           (GCond                *cond,
                                   GMutex               *mutex);
  gboolean (*cond_timed_wait)     (GCond                *cond,
                                   GMutex               *mutex,
                                   GTimeVal             *end_time);
  void      (*cond_free)          (GCond                *cond);
  GPrivate* (*private_new)        (GDestroyNotify        destructor);
  gpointer  (*private_get)        (GPrivate             *private_key);
  void      (*private_set)        (GPrivate             *private_key,
                                   gpointer              data);
  void      (*thread_create)      (GThreadFunc           func,
                                   gpointer              data,
                                   gulong                stack_size,
                                   gboolean              joinable,
                                   gboolean              bound,
                                   GThreadPriority       priority,
                                   gpointer              thread,
                                   GError              **error);
  void      (*thread_yield)       (void);
  void      (*thread_join)        (gpointer              thread);
  void      (*thread_exit)        (void);
  void      (*thread_set_priority)(gpointer              thread,
                                   GThreadPriority       priority);
  void      (*thread_self)        (gpointer              thread);
  gboolean  (*thread_equal)       (gpointer              thread1,
				   gpointer              thread2);
};

 

定义一些宏来访问这些成员变量:

/* shorthands for conditional and unconditional function calls */

#define G_THREAD_UF(op, arglist)					\
    (*g_thread_functions_for_glib_use . op) arglist
#define G_THREAD_CF(op, fail, arg)					\
    (g_thread_supported () ? G_THREAD_UF (op, arg) : (fail))
#define G_THREAD_ECF(op, fail, mutex, type)				\
    (g_thread_supported () ? 						\
      ((type(*)(GMutex*, const gulong, gchar const*))			\
      (*g_thread_functions_for_glib_use . op))				\
     (mutex, G_MUTEX_DEBUG_MAGIC, G_STRLOC) : (fail))

#ifndef G_ERRORCHECK_MUTEXES
# define g_mutex_lock(mutex)						\
    G_THREAD_CF (mutex_lock,     (void)0, (mutex))
# define g_mutex_trylock(mutex)						\
    G_THREAD_CF (mutex_trylock,  TRUE,    (mutex))
# define g_mutex_unlock(mutex)						\
    G_THREAD_CF (mutex_unlock,   (void)0, (mutex))
# define g_mutex_free(mutex)						\
    G_THREAD_CF (mutex_free,     (void)0, (mutex))
# define g_cond_wait(cond, mutex)					\
    G_THREAD_CF (cond_wait,      (void)0, (cond, mutex))
# define g_cond_timed_wait(cond, mutex, abs_time)			\
    G_THREAD_CF (cond_timed_wait, TRUE,   (cond, mutex, abs_time))
#else /* G_ERRORCHECK_MUTEXES */
# define g_mutex_lock(mutex)						\
    G_THREAD_ECF (mutex_lock,    (void)0, (mutex), void)
# define g_mutex_trylock(mutex)						\
    G_THREAD_ECF (mutex_trylock, TRUE,    (mutex), gboolean)
# define g_mutex_unlock(mutex)						\
    G_THREAD_ECF (mutex_unlock,  (void)0, (mutex), void)
# define g_mutex_free(mutex)						\
    G_THREAD_ECF (mutex_free,    (void)0, (mutex), void)
# define g_cond_wait(cond, mutex)					\
    (g_thread_supported () ? ((void(*)(GCond*, GMutex*, gulong, gchar*))\
      g_thread_functions_for_glib_use.cond_wait)			\
        (cond, mutex, G_MUTEX_DEBUG_MAGIC, G_STRLOC) : (void) 0)
# define g_cond_timed_wait(cond, mutex, abs_time)			\
    (g_thread_supported () ?						\
      ((gboolean(*)(GCond*, GMutex*, GTimeVal*, gulong, gchar*))	\
        g_thread_functions_for_glib_use.cond_timed_wait)		\
          (cond, mutex, abs_time, G_MUTEX_DEBUG_MAGIC, G_STRLOC) : TRUE)
#endif /* G_ERRORCHECK_MUTEXES */

#if defined(G_THREADS_ENABLED) && defined(G_THREADS_MANDATORY)
#define g_thread_supported()     1
#else
#define g_thread_supported()    (g_threads_got_initialized)
#endif
#define g_mutex_new()            G_THREAD_UF (mutex_new,      ())
#define g_cond_new()             G_THREAD_UF (cond_new,       ())
#define g_cond_signal(cond)      G_THREAD_CF (cond_signal,    (void)0, (cond))
#define g_cond_broadcast(cond)   G_THREAD_CF (cond_broadcast, (void)0, (cond))
#define g_cond_free(cond)        G_THREAD_CF (cond_free,      (void)0, (cond))
#define g_private_new(destructor) G_THREAD_UF (private_new, (destructor))
#define g_private_get(private_key) G_THREAD_CF (private_get, \
                                                ((gpointer)private_key), \
                                                (private_key))
#define g_private_set(private_key, value) G_THREAD_CF (private_set, \
                                                       (void) (private_key = \
                                                        (GPrivate*) (value)), \
                                                       (private_key, value))
#define g_thread_yield()              G_THREAD_CF (thread_yield, (void)0, ())

#define g_thread_create(func, data, joinable, error)			\
  (g_thread_create_full (func, data, 0, joinable, FALSE, 		\
                         G_THREAD_PRIORITY_NORMAL, error))

 

 

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