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<concept id="GUID-A9A8C0C1-4B89-40FE-917E-7D4F7387DDA9" xml:lang="en"><title>Using

GThreads</title><shortdesc/><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>GLib threads provide a portable way of writing multi-threaded applications.

There are:</p>

<ul>

<li><p>primitives for mutexes to protect concurrent accesses to portions of

the memory</p></li>

<li><p>primitives for conditional variables to allow synchronization between

threads</p></li>

<li><p>primitives for thread-private data that every thread has an instance

of</p></li>

<li><p>APIs for creating and managing threads. </p></li>

</ul>

<p>To use thread-related APIs the application must link to <filepath>libgthread.lib</filepath>.

The function <codeph>g_thread_init()</codeph> must be called to initialize

the thread system before calling any other thread-related functions.</p>

<note>The function <codeph>g_thread_init()</codeph> must be called only once.

The second call to it will abort the application.</note>

<p>The code given below verifies whether the thread system is initialized.</p>

<codeblock xml:space="preserve">if (!g_thread_supported ()) 

	g_thread_init (NULL);

</codeblock>

<p><codeph>g_thread_init()</codeph> can be called with a non-NULL parameter;

however, the user must be sure of what is done since this will override the

default thread implementation.</p>

<p>The following example code explains the usage of some of the thread APIs.

In the example code, create <codeph>NTHREADS</codeph> thread and wait in the

main thread for all the threads to start before proceeding with some other

work. Finally, join to all the threads so that the main thread waits for all

the other threads to terminate.</p>

<codeblock xml:space="preserve">#include &lt;glib.h&gt;

/* g_mutex_lock is a macro that uses the dll global variable

 * g_thread_functions_for_glib_use. To use the global variable

 * we must include glib_global.h.

 */

#include <glib_global.h> // Always include as the last include.

#define NTHREADS 5

int no_threads = 0;

GMutex *mutex;

GCond *cond; 

void* thread_function(void *data)

{

	/*

	.

	local data declaration

	.

	 */

	// lock on the mutex before changing the global variable no_threads

	g_mutex_lock(mutex);

	no_threads++;

	//do a broadcast on the conditional variable once NTHREDS have been created

	if(no_threads == NTHREADS)

		g_cond_broadcast(cond);

	//unlock the mutex

	g_mutex_unlock(mutex);

	/*

	.

	some code

	.

	 */

	return NULL;

}

int main ()

{

	int i;

	GThread *thread[NTHREADS];

	/*

	 .

	 other local data declaration

	 .

 	 */ 

	if(!g_thread_supported())

		g_thread_init (NULL);

	mutex = g_mutex_new ();

	cond = g_cond_new (); 

	for(i=0; i<NTHREADS; i++)

		thread[i] = g_thread_create(thread_function, NULL,TRUE, NULL);

	g_mutex_lock (mutex);

	if (no_threads < NTHREADS)

g_cond_wait (cond, mutex);

	g_mutex_unlock (mutex);

	/*

	.

	some code

	.

	 */

	for(i=0; i<NTHREADS; i++)

		g_thread_join(thread[i]);

	g_mutex_free(mutex);

	g_cond_free(cond);

	/*

	.

	some code

	.

	 */

	return 0;

}

</codeblock>