Add --break-at-isolate-spawn to help with isolate debugging.

runtime/vm/isolate.cc

 // Copyright (c) 2013, 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/isolate.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/json.h"
 #include "vm/code_observers.h"
@@ skipping 25 matching lines @@
 
 
 namespace dart {
 
 DEFINE_FLAG(bool, trace_isolates, false,
             "Trace isolate creation and shut down.");
 DEFINE_FLAG(bool, pause_isolates_on_start, false,
             "Pause isolates before starting.");
 DEFINE_FLAG(bool, pause_isolates_on_exit, false,
             "Pause isolates exiting.");
+DEFINE_FLAG(bool, break_at_isolate_spawn, false,
+            "Insert a one-time breakpoint at the entrypoint for all spawned "
+            "isolates");
 
 
 // Quick access to the locally defined isolate() method.
 #define I (isolate())
 
 
 void Isolate::RegisterClass(const Class& cls) {
   class_table()->Register(cls);
 }
 
@@ skipping 773 matching lines @@
     bool is_spawn_uri = state->is_spawn_uri();
     if (result.IsError()) {
       StoreError(isolate, result);
       return false;
     }
     ASSERT(result.IsFunction());
     Function& func = Function::Handle(isolate);
     func ^= result.raw();
     func = func.ImplicitClosureFunction();
 
+    // TODO(turnidge): Currently we need a way to force a one-time
+    // breakpoint for all spawned isolates to support isolate
+    // debugging.  Remove this once the vmservice becomes the standard
+    // way to debug.
+    if (FLAG_break_at_isolate_spawn) {
+      isolate->debugger()->OneTimeBreakAtEntry(func);
+    }
+
     const Array& capabilities = Array::Handle(Array::New(2));
     Capability& capability = Capability::Handle();
     capability = Capability::New(isolate->pause_capability());
     capabilities.SetAt(0, capability);
     capability = Capability::New(isolate->terminate_capability());
     capabilities.SetAt(1, capability);
 
     // Instead of directly invoking the entry point we call '_startIsolate' with
     // the entry point as argument.
     // Since this function ("RunIsolate") is used for both Isolate.spawn and
@@ skipping 693 matching lines @@
                            serialized_message_, serialized_message_len_);
 }
 
 
 void IsolateSpawnState::Cleanup() {
   SwitchIsolateScope switch_scope(I);
   Dart::ShutdownIsolate();
 }
 
 }  // namespace dart