Add necessary support functions so that embedders can implemented pause on start and exit

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 "include/dart_native_api.h"
 #include "platform/assert.h"
 #include "platform/text_buffer.h"
@@ skipping 761 matching lines @@
       flags_(),
       random_(),
       simulator_(NULL),
       mutex_(new Mutex()),
       saved_stack_limit_(0),
       stack_overflow_flags_(0),
       stack_overflow_count_(0),
       message_handler_(NULL),
       spawn_state_(NULL),
       is_runnable_(false),
+      pause_isolates_flags_overridden_(false),
       gc_prologue_callback_(NULL),
       gc_epilogue_callback_(NULL),
       defer_finalization_count_(0),
       deopt_context_(NULL),
       compiler_stats_(NULL),
       is_service_isolate_(false),
       stacktrace_(NULL),
       stack_frame_index_(-1),
       last_allocationprofile_accumulator_reset_timestamp_(0),
       last_allocationprofile_gc_timestamp_(0),
@@ skipping 270 matching lines @@
   MutexLocker ml(mutex_);
   // Check if we are in a valid state to make the isolate runnable.
   if (is_runnable() == true) {
     return false;  // Already runnable.
   }
   // Set the isolate as runnable and if we are being spawned schedule
   // isolate on thread pool for execution.
   ASSERT(object_store()->root_library() != Library::null());
   set_is_runnable(true);
   if (!ServiceIsolate::IsServiceIsolate(this)) {
-    message_handler()->set_pause_on_start(FLAG_pause_isolates_on_start);
-    message_handler()->set_pause_on_exit(FLAG_pause_isolates_on_exit);
+    if (!pause_isolates_flags_overridden_) {
+      message_handler()->set_pause_on_start(FLAG_pause_isolates_on_start);
+      message_handler()->set_pause_on_exit(FLAG_pause_isolates_on_exit);
+    }

[turnidge, 2016/02/03 21:33:36]

As discussed offline, we may be able to remove pause_isolates_flags_overridden_.

We would move the initialization of pause_on_start/pause_on_exit to the
constructor for the message handler.  Then, inside the message handler, we could
use the runnable bit to determine whether or not we should look at the value...

[turnidge, 2016/02/03 21:35:53]

One more thing, we wouldn't want pause_on_start to ever happen for native
message handlers, so we would probably guard the whole thing in an isolate() !=
NULL...

[Cutch, 2016/02/03 23:04:04]

Acknowledged.

[Cutch, 2016/02/03 23:04:05]

Done.

     if (FLAG_pause_isolates_on_unhandled_exceptions) {
       debugger()->SetExceptionPauseInfo(kPauseOnUnhandledExceptions);
     }
   }
   IsolateSpawnState* state = spawn_state();
   if (state != NULL) {
     ASSERT(this == state->isolate());
     Run();
   }
   TimelineStream* stream = GetIsolateStream();
@@ skipping 1548 matching lines @@
 void IsolateSpawnState::DecrementSpawnCount() {
   ASSERT(spawn_count_monitor_ != NULL);
   ASSERT(spawn_count_ != NULL);
   MonitorLocker ml(spawn_count_monitor_);
   ASSERT(*spawn_count_ > 0);
   *spawn_count_ = *spawn_count_ - 1;
   ml.Notify();
 }
 
 }  // namespace dart