Handle thread preemption in debugger

src/execution.cc

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 505 matching lines @@
   return Handle<String>::cast(result);
 }
 
 
 static Object* RuntimePreempt() {
   // Clear the preempt request flag.
   StackGuard::Continue(PREEMPT);
 
   ContextSwitcher::PreemptionReceived();
 
-  {
+  if (Debug::InDebugger()) {
+    // If currently in the debugger don't do any actual preemption but record
+    // that preemption occoured while in the debugger.
+    Debug::PreemptionWhileInDebugger();
+  } else {
+    // Perform preemption.
     v8::Unlocker unlocker;
     Thread::YieldCPU();
   }
 
   return Heap::undefined_value();
 }
 
 
 Object* Execution::DebugBreakHelper() {
   // Just continue if breaks are disabled.
@@ skipping 58 matching lines @@
   // All allocation spaces other than NEW_SPACE have the same effect.
   Heap::CollectGarbage(0, OLD_DATA_SPACE);
   return v8::Undefined();
 }
 
 
 static GCExtension kGCExtension;
 v8::DeclareExtension kGCExtensionDeclaration(&kGCExtension);
 
 } }  // namespace v8::internal