2 files changed, 82 insertions, 0 deletions

diff --git a/source/blender/imbuf/IMB_thumbs.h b/source/blender/imbuf/IMB_thumbs.h
index f2f75973bcd..13237fe26a1 100644
--- a/source/blender/imbuf/IMB_thumbs.h
+++ b/source/blender/imbuf/IMB_thumbs.h
@@ -91,6 +91,12 @@ void   IMB_thumb_overlay_blend(unsigned int *thumb, int width, int height, float
 ImBuf *IMB_thumb_load_font(const char *filename, unsigned int x, unsigned int y);
 bool IMB_thumb_load_font_get_hash(char *r_hash);
 
+/* Threading */
+void IMB_thumb_locks_acquire(void);
+void IMB_thumb_locks_release(void);
+void IMB_thumb_path_lock(const char *path);
+void IMB_thumb_path_unlock(const char *path);
+
 #ifdef __cplusplus
 }
 #endif /* __cplusplus */
diff --git a/source/blender/imbuf/intern/thumbs.c b/source/blender/imbuf/intern/thumbs.c
index 1fb6c7631b9..f67718ffcba 100644
--- a/source/blender/imbuf/intern/thumbs.c
+++ b/source/blender/imbuf/intern/thumbs.c
@@ -32,12 +32,16 @@
 #include <stdio.h>
 #include <stdlib.h>
 
+#include "MEM_guardedalloc.h"
+
 #include "BLI_utildefines.h"
 #include "BLI_string.h"
 #include "BLI_path_util.h"
 #include "BLI_fileops.h"
+#include "BLI_ghash.h"
 #include "BLI_hash_md5.h"
 #include "BLI_system.h"
+#include "BLI_threads.h"
 #include BLI_SYSTEM_PID_H
 
 #include "IMB_imbuf_types.h"
@@ -618,3 +622,75 @@ ImBuf *IMB_thumb_manage(const char *org_path, ThumbSize size, ThumbSource source
 
 	return img;
 }
+
+/* ***** Threading ***** */
+/* Thumbnail handling is not really threadsafe in itself.
+ * However, as long as we do not operate on the same file, we shall have no collision.
+ * So idea is to 'lock' a given source file path.
+ */
+
+static struct IMBThumbLocks {
+	GSet *locked_paths;
+	int lock_counter;
+	ThreadCondition cond;
+} thumb_locks = {0};
+
+void IMB_thumb_locks_acquire(void) {
+	BLI_lock_thread(LOCK_IMAGE);
+
+	if (thumb_locks.lock_counter == 0) {
+		BLI_assert(thumb_locks.locked_paths == NULL);
+		thumb_locks.locked_paths = BLI_gset_str_new(__func__);
+		BLI_condition_init(&thumb_locks.cond);
+	}
+	thumb_locks.lock_counter++;
+
+	BLI_assert(thumb_locks.locked_paths != NULL);
+	BLI_assert(thumb_locks.lock_counter > 0);
+	BLI_unlock_thread(LOCK_IMAGE);
+}
+
+void IMB_thumb_locks_release(void) {
+	BLI_lock_thread(LOCK_IMAGE);
+	BLI_assert((thumb_locks.locked_paths != NULL) && (thumb_locks.lock_counter > 0));
+
+	thumb_locks.lock_counter--;
+	if (thumb_locks.lock_counter == 0) {
+		BLI_gset_free(thumb_locks.locked_paths, MEM_freeN);
+		thumb_locks.locked_paths = NULL;
+		BLI_condition_end(&thumb_locks.cond);
+	}
+
+	BLI_unlock_thread(LOCK_IMAGE);
+}
+
+void IMB_thumb_path_lock(const char *path) {
+	void *key = BLI_strdup(path);
+
+	BLI_lock_thread(LOCK_IMAGE);
+	BLI_assert((thumb_locks.locked_paths != NULL) && (thumb_locks.lock_counter > 0));
+
+	if (thumb_locks.locked_paths) {
+		while (!BLI_gset_add(thumb_locks.locked_paths, key)) {
+			BLI_condition_wait_global_mutex(&thumb_locks.cond, LOCK_IMAGE);
+		}
+	}
+
+	BLI_unlock_thread(LOCK_IMAGE);
+}
+
+void IMB_thumb_path_unlock(const char *path) {
+	const void *key = path;
+
+	BLI_lock_thread(LOCK_IMAGE);
+	BLI_assert((thumb_locks.locked_paths != NULL) && (thumb_locks.lock_counter > 0));
+
+	if (thumb_locks.locked_paths) {
+		if (!BLI_gset_remove(thumb_locks.locked_paths, key, MEM_freeN)) {
+			BLI_assert(0);
+		}
+		BLI_condition_notify_all(&thumb_locks.cond);
+	}
+
+	BLI_unlock_thread(LOCK_IMAGE);
+}