Fix T37980: Multiple font objects sharing an external font gives problems

Solved by adding RW lock to BKE_vfont_to_curve.

So now all the threads are allowed to read chars from ghash,
but they'll be locked as soon as one thread would need to load
more chars from font to the ghash.

2 files changed, 16 insertions, 1 deletions

diff --git a/source/blender/blenkernel/intern/font.c b/source/blender/blenkernel/intern/font.c
index 608d5a72756..6256c878d8d 100644
--- a/source/blender/blenkernel/intern/font.c
+++ b/source/blender/blenkernel/intern/font.c
@@ -65,6 +65,7 @@
 #include "BKE_displist.h"
 
 static ThreadMutex vfont_mutex = BLI_MUTEX_INITIALIZER;
+static ThreadRWMutex vfont_rwlock = BLI_RWLOCK_INITIALIZER;
 
 /* The vfont code */
 void BKE_vfont_free_data(struct VFont *vfont)
@@ -595,7 +596,9 @@ makebreak:
 		if (vfont == NULL) break;
 
 		if (!ELEM(ascii, '\n', '\0')) {
+			BLI_rw_mutex_lock(&vfont_rwlock, THREAD_LOCK_READ);
 			che = find_vfont_char(vfd, ascii);
+			BLI_rw_mutex_unlock(&vfont_rwlock);
 
 			/*
 			 * The character wasn't in the current curve base so load it
@@ -603,7 +606,17 @@ makebreak:
 			 * whole font is in the memory already
 			 */
 			if (che == NULL && BKE_vfont_is_builtin(vfont) == false) {
-				che = BLI_vfontchar_from_freetypefont(vfont, ascii);
+				BLI_rw_mutex_lock(&vfont_rwlock, THREAD_LOCK_WRITE);
+				/* Check it once again, char might have been already load
+				 * between previous BLI_rw_mutex_unlock() and this BLI_rw_mutex_lock().
+				 *
+				 * Such a check should not be a bottleneck since it wouldn't
+				 * happen often once all the chars are load.
+				 */
+				if ((che = find_vfont_char(vfd, ascii)) == NULL) {
+					che = BLI_vfontchar_from_freetypefont(vfont, ascii);
+				}
+				BLI_rw_mutex_unlock(&vfont_rwlock);
 			}
 		}
 		else {
diff --git a/source/blender/blenlib/BLI_threads.h b/source/blender/blenlib/BLI_threads.h
index 7a3ee1dd0f4..3ccfcc023da 100644
--- a/source/blender/blenlib/BLI_threads.h
+++ b/source/blender/blenlib/BLI_threads.h
@@ -125,6 +125,8 @@ void BLI_spin_end(SpinLock *spin);
 #define THREAD_LOCK_READ    1
 #define THREAD_LOCK_WRITE   2
 
+#define BLI_RWLOCK_INITIALIZER PTHREAD_RWLOCK_INITIALIZER
+
 typedef pthread_rwlock_t ThreadRWMutex;
 
 void BLI_rw_mutex_init(ThreadRWMutex *mutex);