[vm] Make the crash reporter more resilient to crashes during safepoints.

runtime/vm/profiler.cc

Index: runtime/vm/profiler.cc
diff --git a/runtime/vm/profiler.cc b/runtime/vm/profiler.cc
index a3fb9c6c90a7e83438908ef7d0907464d963b576..4de16a6926020198433bad805e8ddf01a2070a56 100644
--- a/runtime/vm/profiler.cc
+++ b/runtime/vm/profiler.cc
@@ -406,17 +406,22 @@ void ClearProfileVisitor::VisitSample(Sample* sample) {
 }
 
 static void DumpStackFrame(intptr_t frame_index, uword pc) {
-  Isolate* isolate = Isolate::Current();
-  if ((isolate != NULL) && isolate->is_runnable()) {
-    Code& code = Code::Handle(Code::LookupCodeInVmIsolate(pc));
-    if (!code.IsNull()) {
-      OS::PrintErr("  [0x%" Pp "] %s\n", pc, code.QualifiedName());
-      return;
-    }
-    code = Code::LookupCode(pc);
-    if (!code.IsNull()) {
-      OS::PrintErr("  [0x%" Pp "] %s\n", pc, code.QualifiedName());
-      return;
+  Thread* thread = Thread::Current();
+  if ((thread != NULL) && !thread->IsAtSafepoint()) {
+    Isolate* isolate = thread->isolate();
+    if ((isolate != NULL) && isolate->is_runnable()) {
+      // Attempt to symbolize Dart frames if we have can safely iterate the
+      // current isolate's heap.

[danunez, 2017/08/08 20:44:02]

This comment is unclear to me. It reads like there is a word missing.

[rmacnak, 2017/08/09 17:58:39]

Deleted "have"

+      Code& code = Code::Handle(Code::LookupCodeInVmIsolate(pc));
+      if (!code.IsNull()) {
+        OS::PrintErr("  [0x%" Pp "] %s\n", pc, code.QualifiedName());
+        return;
+      }
+      code = Code::LookupCode(pc);
+      if (!code.IsNull()) {
+        OS::PrintErr("  [0x%" Pp "] %s\n", pc, code.QualifiedName());
+        return;
+      }

[siva, 2017/08/08 23:59:55]

why not 

Code& code = Code::Handle(Code::LookupCodeInVmIsolate(pc));
if (code.IsNull()) {
  code = Code::LookupCode(pc);
}
if (!code.IsNull()) {
  OS::PrintErr("  [0x%" Pp "] %s\n", pc, code.QualifiedName());
  return;
}

[rmacnak, 2017/08/09 17:58:39]

Done.

     }
   }