Compositor: Use atomics to update finished tiles progress

Integer is not safe for incremental by multiple threads and if one is unlucky
enough that could cause progress re[reports to go totally nuts.

source/blender/compositor/CMakeLists.txt

@@ -41,6 +41,7 @@ set(INC
 	../render/intern/include
 	../../../extern/clew/include
 	../../../intern/guardedalloc
+	../../../intern/atomic
 )
 
 set(INC_SYS

source/blender/compositor/SConscript

@@ -50,6 +50,7 @@ incs = [
     '../render/intern/include',
     '../windowmanager',
     '../../../intern/guardedalloc',
+    '../../../intern/atomic',
 
     # data files
     env['DATA_HEADERS'],

source/blender/compositor/intern/COM_ExecutionGroup.cpp

@@ -44,6 +44,8 @@
 #include "WM_api.h"
 #include "WM_types.h"
 
+#include "atomic_ops.h"
+
 ExecutionGroup::ExecutionGroup()
 {
 	this->m_isOutput = false;
@@ -382,7 +384,7 @@ void ExecutionGroup::finalizeChunkExecution(int chunkNumber, MemoryBuffer **memo
 	if (this->m_chunkExecutionStates[chunkNumber] == COM_ES_SCHEDULED)
 		this->m_chunkExecutionStates[chunkNumber] = COM_ES_EXECUTED;
 	
-	this->m_chunksFinished++;
+	atomic_add_u(&this->m_chunksFinished, 0);
 	if (memoryBuffers) {
 		for (unsigned int index = 0; index < this->m_cachedMaxReadBufferOffset; index++) {
 			MemoryBuffer *buffer = memoryBuffers[index];