Based on Sergey's suggestion, use spinlocks for threaded loading of

waveforms.

source/blender/blenkernel/intern/sound.c

@@ -118,9 +118,10 @@ void BKE_sound_free(bSound *sound)
 
 	sound_free_waveform(sound);
 	
-	if (sound->mutex) {
+	if (sound->spinlock) {
-		BLI_mutex_free(sound->mutex);
+		BLI_spin_end(sound->spinlock);
-		sound->mutex = NULL;
+		MEM_freeN(sound->spinlock);
+		sound->spinlock = NULL;
 	}
 	
 #endif  /* WITH_AUDASPACE */
@@ -709,18 +710,18 @@ void sound_read_waveform(bSound *sound, short *stop)
 			MEM_freeN(waveform->data);
 		}
 		MEM_freeN(waveform);
-		BLI_mutex_lock(sound->mutex);
+		BLI_spin_lock(sound->spinlock);
 		sound->flags &= ~SOUND_FLAGS_WAVEFORM_LOADING;
-		BLI_mutex_unlock(sound->mutex);
+		BLI_spin_unlock(sound->spinlock);
 		return;
 	}
 		
 	sound_free_waveform(sound);
 	
-	BLI_mutex_lock(sound->mutex);
+	BLI_spin_lock(sound->spinlock);
 	sound->waveform = waveform;
 	sound->flags &= ~SOUND_FLAGS_WAVEFORM_LOADING;
-	BLI_mutex_unlock(sound->mutex);
+	BLI_spin_unlock(sound->spinlock);
 }
 
 void sound_update_scene(Main *bmain, struct Scene *scene)

source/blender/blenloader/intern/readfile.c

@@ -6872,9 +6872,10 @@ static void direct_link_sound(FileData *fd, bSound *sound)
 		sound->waveform = NULL;
 	}
 		
-	if (sound->mutex)
+	if (sound->spinlock) {
-		sound->mutex = BLI_mutex_alloc();
+		sound->spinlock = MEM_mallocN(sizeof(SpinLock), "sound_spinlock");
-	
+		BLI_spin_init(sound->spinlock);
+	}
 	/* clear waveform loading flag */
 	sound->flags &= ~SOUND_FLAGS_WAVEFORM_LOADING;
 

source/blender/editors/space_sequencer/sequencer_draw.c

@@ -70,6 +70,7 @@
 
 #include "WM_api.h"
 
+#include "MEM_guardedalloc.h"
 
 /* own include */
 #include "sequencer_intern.h"
@@ -200,23 +201,25 @@ static void drawseqwave(const bContext *C, SpaceSeq *sseq, Scene *scene, Sequenc
 		
 		SoundWaveform *waveform;
 		
-		if (!sound->mutex)
+		if (!sound->spinlock) {
-			sound->mutex = BLI_mutex_alloc();
+			sound->spinlock = MEM_mallocN(sizeof(SpinLock), "sound_spinlock");
+			BLI_spin_init(sound->spinlock);
+		}
 		
-		BLI_mutex_lock(sound->mutex);
+		BLI_spin_lock(sound->spinlock);
 		if (!seq->sound->waveform) {
 			if (!(sound->flags & SOUND_FLAGS_WAVEFORM_LOADING)) {
 				/* prevent sounds from reloading */
 				seq->sound->flags |= SOUND_FLAGS_WAVEFORM_LOADING;
-				BLI_mutex_unlock(sound->mutex);
+				BLI_spin_unlock(sound->spinlock);
 				sequencer_preview_add_sound(C, seq);
 			}
 			else {
-				BLI_mutex_unlock(sound->mutex);
+				BLI_spin_unlock(sound->spinlock);
 			}
 			return;  /* nothing to draw */
 		}
-		BLI_mutex_unlock(sound->mutex);
+		BLI_spin_unlock(sound->spinlock);
 		
 		waveform = seq->sound->waveform;
 		

source/blender/editors/space_sequencer/sequencer_preview.c

@@ -95,9 +95,9 @@ static void preview_startjob(void *data, short *stop, short *do_update, float *p
 				sound = previewjb->sound;
 
 				/* make sure we cleanup the loading flag! */
-				BLI_mutex_lock(sound->mutex);
+				BLI_spin_lock(sound->spinlock);
 				sound->flags &= ~SOUND_FLAGS_WAVEFORM_LOADING;
-				BLI_mutex_unlock(sound->mutex);
+				BLI_spin_unlock(sound->spinlock);
 				
 				BLI_mutex_lock(pj->mutex);
 				previewjb = previewjb->next;

source/blender/makesdna/DNA_sound_types.h

@@ -95,8 +95,8 @@ typedef struct bSound {
 	 */
 	void *playback_handle;
 
-	/* mutex for asynchronous loading of sounds */
+	/* spinlock for asynchronous loading of sounds */
-	void *mutex;
+	void *spinlock;
 	/* XXX unused currently	(SOUND_TYPE_LIMITER) */
 	/* float start, end; */
 } bSound;