VSE: Process audio strips waveforms in parallel

A TaskPool is used to execute tasks in the backghround.

Whenever a new audio strip needs their waveform to be computed, it's
added as a task to the TaskPool.

Once the PreviewJob has submitted all available tasks to the task pool,
it waits for all of them to finish before exiting.

The TaskPool is configured to start tasks as soon as they are pushed
onto the task queue.

@@ -23,6 +24,8 @@
 
 #include "MEM_guardedalloc.h"
 
+#include "atomic_ops.h"

@@ -44,1 +49,4 @@
 
+typedef struct ReadSoundWaveformTask {
+  PreviewJob *wm_job;
+  bool *wm_do_update;

@@ -57,2 +109,3 @@
+  TaskPool *task_pool = BLI_task_pool_create(NULL, TASK_PRIORITY_LOW);
   PreviewJob *pj = data;
-  PreviewJobAudio *previewjb;
+  bool keep_looping = true;

@@ -67,0 +117,4 @@
+  while (keep_looping) {
+    /* Wait until there's either a new audio job to process or one of the previously submitted jobs is done.*/
+    BLI_mutex_lock(pj->mutex);
+    while (pj->previews.first == NULL && previous_processed == pj->processed) {

@@ -79,2 +132,2 @@
-        sound->tags &= ~SOUND_TAGS_WAVEFORM_LOADING;
-        BLI_spin_unlock(sound->spinlock);
+    if (pj->processed == pj->total) {
+      keep_looping = false;

@@ -83,2 +138,2 @@
-        previewjb = previewjb->next;
-        BLI_mutex_unlock(pj->mutex);
+      /* Clear all pending jobs data. */
+      for (PreviewJobAudio *previewjb = pj->previews.first; previewjb != NULL; previewjb = previewjb->next) {

@@ -91,0 +148,4 @@
+    } else {
+      /* Push all available jobs to the processing queue. */
+      PreviewJobAudio *previewjb = pj->previews.first;
+      while (previewjb) {

@@ -130,0 +199,4 @@
+    BLI_mutex_lock(pj->mutex);
+
+    /* If the job exists but is not running, bail and try again on the next draw call. */
+    if (!pj->running) {

@@ -102,0 +165,4 @@
+      PreviewJobAudio *next_previewjb = previewjb->next;
+      BLI_remlink(&pj->previews, previewjb);
+
+      previewjb = next_previewjb;