1. Avoid potential dead lock due to lock-order-inversion

runtime/vm/heap.cc

Index: runtime/vm/heap.cc
diff --git a/runtime/vm/heap.cc b/runtime/vm/heap.cc
index da9e6790dab711e48223c9b4c9528e6d4d02be9b..23a380b5f90a9c1415a487722e8b4e32319a40cb 100644
--- a/runtime/vm/heap.cc
+++ b/runtime/vm/heap.cc
@@ -88,13 +88,13 @@ uword Heap::AllocateOld(intptr_t size, HeapPage::PageType type) {
   Thread* thread = Thread::Current();
   if (thread->CanCollectGarbage()) {
     {

[Vyacheslav Egorov (Google), 2016/12/31 11:09:48]

this block of code is repeated twice - maybe make a helper function?

[siva, 2017/01/05 19:06:10]

Done.

+      // Wait for any GC tasks that are in progress.
       MonitorLocker ml(old_space_.tasks_lock());
-      addr = old_space_.TryAllocate(size, type);
-      while ((addr == 0) && (old_space_.tasks() > 0)) {
+      while (old_space_.tasks() > 0) {
         ml.WaitWithSafepointCheck(thread);
-        addr = old_space_.TryAllocate(size, type);
       }
     }
+    addr = old_space_.TryAllocate(size, type);
     if (addr != 0) {
       return addr;
     }
@@ -107,12 +107,11 @@ uword Heap::AllocateOld(intptr_t size, HeapPage::PageType type) {
     // Wait for all of the concurrent tasks to finish before giving up.
     {
       MonitorLocker ml(old_space_.tasks_lock());
-      addr = old_space_.TryAllocate(size, type);
-      while ((addr == 0) && (old_space_.tasks() > 0)) {
+      while (old_space_.tasks() > 0) {
         ml.WaitWithSafepointCheck(thread);
-        addr = old_space_.TryAllocate(size, type);
       }
     }
+    addr = old_space_.TryAllocate(size, type);
     if (addr != 0) {
       return addr;
     }