improve compat with ancient glibs

and fix a tiny threading leak

ChangeLog

@@ -1,5 +1,7 @@
 18/10/16 started 8.4.3
 - fix error detection in gif_close, thanks aaron42net
+- fix tiny threading memleak
+- improve compatibility with very old glib, see #548
 
 27/9/16 started 8.4.2
 - small doc improvements

libvips/include/vips/internal.h

@@ -102,6 +102,8 @@ extern char *vips__cache_max_files;
 extern gboolean vips__cache_dump;
 extern gboolean vips__cache_trace;
 
+void vips__threadpool_init( void );
+
 void vips__cache_init( void );
 
 void vips__print_renders( void );

libvips/iofuncs/buffer.c

@@ -712,7 +712,7 @@ buffer_thread_destroy_notify( VipsBufferThread *buffer_thread )
 	buffer_thread_free( buffer_thread );
 }
 
-/* Init the buffer cache system.
+/* Init the buffer cache system. This is called during vips_init.
  */
 void
 vips__buffer_init( void )

libvips/iofuncs/init.c

@@ -302,6 +302,9 @@ vips_init( const char *argv0 )
 		g_thread_init( NULL );
 #endif 
 
+	vips__threadpool_init();
+	vips__buffer_init();
+
 	/* This does an unsynchronised static hash table init on first call --
 	 * we have to make sure we do this single-threaded. See: 
 	 * https://github.com/openslide/openslide/issues/161

libvips/iofuncs/threadpool.c

@@ -101,7 +101,7 @@ int vips__concurrency = 0;
 
 /* Set this GPrivate to indicate that this is a vips worker.
  */
-static GPrivate vips_threadpool_is_worker_private;
+static GPrivate *is_worker_key = NULL;
 
 /* Glib 2.32 revised the thread API. We need some compat functions.
  */
@@ -165,7 +165,7 @@ vips_g_cond_free( GCond *cond )
 gboolean
 vips_thread_isworker( void )
 {
-	return( g_private_get( &vips_threadpool_is_worker_private ) != NULL );
+	return( g_private_get( is_worker_key ) != NULL );
 }
 
 typedef struct {
@@ -181,12 +181,12 @@ vips_thread_run( gpointer data )
 
 	void *result;
 
-	if( vips__thread_profile ) 
-		vips__thread_profile_attach( info->domain );
-
 	/* Set this to something (anything) to tag this thread as a vips worker.
 	 */
-	g_private_set( &vips_threadpool_is_worker_private, data );
+	g_private_set( is_worker_key, data );
+
+	if( vips__thread_profile ) 
+		vips__thread_profile_attach( info->domain );
 
 	result = info->func( info->data );
 
@@ -940,6 +940,23 @@ vips_threadpool_run( VipsImage *im,
 	return( result );
 }
 
+/* Start up threadpools. This is called during vips_init.
+ */
+void
+vips__threadpool_init( void )
+{
+	/* We need to work with the pre-2.32 threading API.
+	 */
+#ifdef HAVE_PRIVATE_INIT
+	static GPrivate private = { 0 }; 
+
+	is_worker_key = &private;
+#else
+	if( !is_worker_key ) 
+		is_worker_key = g_private_new( NULL ); 
+#endif
+}
+
 /**
  * vips_get_tile_size:
  * @im: image to guess for