Fix for issue 27380 - VM stuck in deadlock with background finalization and background compiler thr…

runtime/vm/heap.cc

Index: runtime/vm/heap.cc
diff --git a/runtime/vm/heap.cc b/runtime/vm/heap.cc
index fd22740abb4cf19fd94ec30ba3dd59720b629247..c3353d276231028b1ad6b2c3730b12b01c241163 100644
--- a/runtime/vm/heap.cc
+++ b/runtime/vm/heap.cc
@@ -89,18 +89,18 @@ uword Heap::AllocateOld(intptr_t size, HeapPage::PageType type) {
   // If we are in the process of running a sweep, wait for the sweeper to free
   // memory.
   Thread* thread = Thread::Current();
-  {
-    MonitorLocker ml(old_space_.tasks_lock());
-    addr = old_space_.TryAllocate(size, type);
-    while ((addr == 0) && (old_space_.tasks() > 0)) {
-      ml.WaitWithSafepointCheck(thread);
+  if (thread->CanCollectGarbage()) {
+    {
+      MonitorLocker ml(old_space_.tasks_lock());
       addr = old_space_.TryAllocate(size, type);
+      while ((addr == 0) && (old_space_.tasks() > 0)) {
+        ml.WaitWithSafepointCheck(thread);
+        addr = old_space_.TryAllocate(size, type);
+      }
+    }
+    if (addr != 0) {
+      return addr;
     }
-  }
-  if (addr != 0) {
-    return addr;
-  }
-  if (thread->CanCollectGarbage()) {
     // All GC tasks finished without allocating successfully. Run a full GC.
     CollectAllGarbage();
     addr = old_space_.TryAllocate(size, type);