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

runtime/vm/heap.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/heap.h"
 
 #include "platform/assert.h"
 #include "platform/utils.h"
 #include "vm/flags.h"
 #include "vm/isolate.h"
@@ skipping 69 matching lines @@
 uword Heap::AllocateOld(intptr_t size, HeapPage::PageType type) {
   ASSERT(Thread::Current()->no_safepoint_scope_depth() == 0);
   uword addr = old_space_.TryAllocate(size, type);
   if (addr != 0) {
     return addr;
   }
   // If we are in the process of running a sweep, wait for the sweeper to free
   // memory.
   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;
     }
     // All GC tasks finished without allocating successfully. Run a full GC.
     CollectAllGarbage();
     addr = old_space_.TryAllocate(size, type);
     if (addr != 0) {
       return addr;
     }
     // 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;
     }
     // Force growth before attempting another synchronous GC.
     addr = old_space_.TryAllocate(size, type, PageSpace::kForceGrowth);
     if (addr != 0) {
       return addr;
     }
     // Before throwing an out-of-memory error try a synchronous GC.
     CollectAllGarbage();
@@ skipping 717 matching lines @@
   Dart::vm_isolate()->heap()->WriteProtect(false);
 }
 
 
 WritableVMIsolateScope::~WritableVMIsolateScope() {
   ASSERT(Dart::vm_isolate()->heap()->UsedInWords(Heap::kNew) == 0);
   Dart::vm_isolate()->heap()->WriteProtect(true);
 }
 
 }  // namespace dart