Reduce CPU usage when no isolates need to be profiled.

runtime/vm/profiler.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 "platform/utils.h"
 
 #include "vm/allocation.h"
 #include "vm/atomic.h"
 #include "vm/code_patcher.h"
 #include "vm/isolate.h"
@@ skipping 1567 matching lines @@
   file_write(buffer->buf(), buffer->length(), f);
   file_close(f);
 }
 
 
 IsolateProfilerData::IsolateProfilerData(SampleBuffer* sample_buffer,
                                          bool own_sample_buffer) {
   ASSERT(sample_buffer != NULL);
   sample_buffer_ = sample_buffer;
   own_sample_buffer_ = own_sample_buffer;
+  block_count_ = 0;
 }
 
 
 IsolateProfilerData::~IsolateProfilerData() {
   if (own_sample_buffer_) {
     delete sample_buffer_;
     sample_buffer_ = NULL;
     own_sample_buffer_ = false;
   }
 }
 
 
+void IsolateProfilerData::Block() {
+  block_count_++;
+}
+
+
+void IsolateProfilerData::Unblock() {
+  block_count_--;

[Ivan Posva, 2014/05/25 12:25:16]

ASSERT that you are not over unblocking.

[Cutch, 2014/05/26 06:59:35]

Added a FATAL.

+  if (!blocked()) {
+    // We just unblocked this isolate, wake up the thread interrupter.
+    ThreadInterrupter::WakeUp();
+  }
+}
+
+
 Sample* SampleBuffer::ReserveSample() {
   ASSERT(samples_ != NULL);
   uintptr_t cursor = AtomicOperations::FetchAndIncrement(&cursor_);
   // Map back into sample buffer range.
   cursor = cursor % capacity_;
   return At(cursor);
 }
 
 
 class ProfilerDartStackWalker : public ValueObject {
@@ skipping 221 matching lines @@
       ProfilerDartStackWalker stackWalker(sample);
       stackWalker.walk();
     } else {
       // TODO(johnmccutchan): Support collecting only Dart frames with
       // ProfilerNativeStackWalker.
     }
   }
 }
 
 }  // namespace dart