improve thread-safety

the cache and link thing now lock, so you can create images and process
them from several threads

libvips/iofuncs/cache.c

@@ -2,6 +2,8 @@
  *
  * 20/6/12
  * 	- try to make it compile on centos5
+ * 7/7/12
+ * 	- add a lock so we can run operations from many threads
  */
 
 /*
@@ -103,6 +105,10 @@ static GHashTable *vips_cache_table = NULL;
  */
 static int vips_cache_time = 0;
 
+/* Protect cache access with this.
+ */
+static GMutex *vips_cache_lock = NULL;
+
 /* Old versions of glib are missing these. When we abandon centos 5, switch to
  * g_int64_hash() and g_double_hash().
  */
@@ -407,6 +413,8 @@ static void
 vips_cache_init( void )
 {
 	if( !vips_cache_table ) {
+		vips_cache_lock = g_mutex_new();
+
 		vips_cache_table = g_hash_table_new( 
 			(GHashFunc) vips_operation_hash, 
 			(GEqualFunc) vips_operation_equal );
@@ -438,7 +446,6 @@ vips_cache_print_fn( void *value, void *a, void *b )
 	return( NULL );
 }
 
-
 /**
  * vips_cache_print:
  *
@@ -447,11 +454,15 @@ vips_cache_print_fn( void *value, void *a, void *b )
 void
 vips_cache_print( void )
 {
+	g_mutex_lock( vips_cache_lock );
+
 	if( vips_cache_table ) {
 		printf( "Operation cache:\n" );
 		vips_hash_table_map( vips_cache_table, 
 			vips_cache_print_fn, NULL, NULL ); 
 	}
+
+	g_mutex_unlock( vips_cache_lock );
 }
 
 static void *
@@ -578,6 +589,8 @@ vips_cache_trim( void )
 {
 	VipsOperation *operation;
 
+	g_mutex_lock( vips_cache_lock );
+
 	while( vips_cache_table &&
 		(g_hash_table_size( vips_cache_table ) > vips_cache_max ||
 		vips_tracked_get_files() > vips_cache_max_files ||
@@ -589,6 +602,8 @@ vips_cache_trim( void )
 
 		vips_cache_drop( operation );
 	}
+
+	g_mutex_unlock( vips_cache_lock );
 }
 
 static void *
@@ -659,6 +674,8 @@ vips_cache_operation_buildp( VipsOperation **operation )
 
 	vips_cache_trim();
 
+	g_mutex_lock( vips_cache_lock );
+
 	if( (hit = g_hash_table_lookup( vips_cache_table, *operation )) ) {
 		if( vips__cache_trace ) {
 			printf( "vips cache: hit %p\n  ", hit );
@@ -672,7 +689,10 @@ vips_cache_operation_buildp( VipsOperation **operation )
 
 		*operation = hit;
 	}
-	else {
+
+	g_mutex_unlock( vips_cache_lock );
+
+	if( !hit ) {
 		if( vips__cache_trace ) {
 			if( (*operation)->nocache ) 
 				printf( "vips cache: uncacheable %p\n  ", 
@@ -685,13 +705,18 @@ vips_cache_operation_buildp( VipsOperation **operation )
 		if( vips_object_build( VIPS_OBJECT( *operation ) ) ) 
 			return( -1 );
 
+		g_mutex_lock( vips_cache_lock );
+
 		if( !(*operation)->nocache ) {
 			vips_cache_ref( *operation );
 			g_hash_table_insert( vips_cache_table, 
 				*operation, *operation );
 		}
+
+		g_mutex_unlock( vips_cache_lock );
 	}
 
+
 	return( 0 );
 }
 

libvips/iofuncs/generate.c

@@ -50,6 +50,9 @@
  * 24/3/11
  * 	- move demand_hint stuff in here
  * 	- move to vips_ namespace
+ * 7/7/12
+ * 	- lock around link make/break so we can process an image from many
+ * 	  threads
  */
 
 /*
@@ -172,10 +175,12 @@ vips__link_break_rev( VipsImage *image_down, VipsImage *image_up )
 void
 vips__link_break_all( VipsImage *image )
 {
+	g_mutex_lock( vips__global_lock );
 	vips_slist_map2( image->upstream, 
 		(VipsSListMap2Fn) vips__link_break, image, NULL );
 	vips_slist_map2( image->downstream, 
 		(VipsSListMap2Fn) vips__link_break_rev, image, NULL );
+	g_mutex_unlock( vips__global_lock );
 
 	g_assert( !image->upstream );
 	g_assert( !image->downstream );
@@ -326,8 +331,10 @@ vips_demand_hint_array( VipsImage *image, VipsDemandStyle hint, VipsImage **in )
 
 	/* im depends on all these ims.
 	 */
+	g_mutex_lock( vips__global_lock );
 	for( i = 0; i < len; i++ )
 		vips__link_make( in[i], image );
+	g_mutex_unlock( vips__global_lock );
 
 	/* Set a flag on the image to say we remembered to call this thing.
 	 * vips_image_generate() and friends check this.

libvips/iofuncs/threadpool.c

@@ -835,9 +835,8 @@ vips_threadpool_create_threads( VipsThreadpool *pool )
  * processed, @progress is called, so that the operation can give
  * progress feedback. @progress may be %NULL.
  *
- * Each thread has private state that the @allocate and @work functions can 
- * use to communicate. This state is created by each worker as it starts using
- * @start. Use the state destructor to clean up.
+ * The object returned by @start must be an instance of a subclass of
+ * #VipsThreadState. Use this to communicate between @allocate and @work. 
  *
  * @allocate and @start are always single-threaded (so they can write to the 
  * per-pool state), whereas @work can be executed concurrently. @progress is