Sampling profiler

runtime/vm/profiler_android.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/globals.h"
+#if defined(TARGET_OS_ANDROID)
+
+#include "vm/profiler.h"
+#include "vm/signal_handler.h"
+
+namespace dart {
+
+DECLARE_FLAG(bool, profile);
+
+static void ProfileSignalAction(int signal, siginfo_t* info, void* context_) {
+  if (signal != SIGPROF) {
+    return;
+  }
+  ucontext_t* context = reinterpret_cast<ucontext_t*>(context_);
+  mcontext_t mcontext = context->uc_mcontext;
+  Isolate* isolate = Isolate::Current();
+  if (isolate == NULL) {
+    return;
+  }
+  {
+    ScopedMutexLock profiler_data_lock(isolate->profiler_data_mutex());
+    IsolateProfilerData* profiler_data = isolate->profiler_data();
+    if (profiler_data == NULL) {
+      return;
+    }
+
+    uintptr_t stack_lower;
+    uintptr_t stack_upper;
+    bool r = isolate->GetStackBounds(&stack_lower, &stack_upper);
+    ASSERT(r);
+    uintptr_t PC = SignalHandler::GetProgramCounter(mcontext);
+    uintptr_t FP = SignalHandler::GetFramePointer(mcontext);
+    uintptr_t SP = SignalHandler::GetStackPointer(mcontext);
+    stack_lower = SignalHandler::GetStackPointer(mcontext);
+    int64_t sample_time = OS::GetCurrentTimeMicros();
+    profiler_data->SampledAt(sample_time);
+    CollectSample(profiler_data, PC, FP, SP, stack_lower, stack_upper);
+  }
+  ProfilerManager::ScheduleIsolate(isolate);
+}
+
+
+int64_t ProfilerManager::SampleAndRescheduleIsolates(int64_t current_time) {
+  if (isolates_size_ == 0) {
+    return 0;
+  }
+  static const int64_t max_time = 0x7fffffffffffffffLL;
+  int64_t lowest = max_time;
+  for (intptr_t i = 0; i < isolates_size_; i++) {
+    Isolate* isolate = isolates_[i];
+    ScopedMutexLock isolate_lock(isolate->profiler_data_mutex());
+    IsolateProfilerData* profiler_data = isolate->profiler_data();
+    ASSERT(profiler_data != NULL);
+    if (profiler_data->ShouldSample(current_time)) {
+      pthread_kill(profiler_data->thread_id(), SIGPROF);
+      RemoveIsolate(i);
+      i--;  // Remove moves the last element into i, this decrement cancels
+            // the increment in the for loop.

[siva, 2013/11/11 03:51:54]

Seems hacky why not use a while loop
while (i < isolates_size_) {
   ....
   .....
   conditionally increment i;
}

[Cutch, 2013/11/18 20:48:54]

Done.

+      continue;
+    }
+    if (profiler_data->CanExpire()) {
+      int64_t isolate_time_left =
+          profiler_data->TimeUntilExpiration(current_time);
+      if (isolate_time_left < 0) {
+        continue;
+      }
+      if (isolate_time_left < lowest) {
+        lowest = isolate_time_left;
+      }
+    }
+  }
+  if (isolates_size_ == 0) {
+    return 0;
+  }
+  if (lowest == max_time) {
+    return 0;
+  }
+  ASSERT(lowest != max_time);
+  ASSERT(lowest > 0);
+  return lowest;
+}
+
+
+void ProfilerManager::ThreadMain(uword parameters) {
+  ASSERT(initialized_);
+  ASSERT(FLAG_profile);
+  SignalHandler::Install(ProfileSignalAction);
+  ScopedMonitorLock lock(monitor_);
+  while (!shutdown_) {
+    int64_t current_time = OS::GetCurrentTimeMicros();
+    int64_t next_sample = SampleAndRescheduleIsolates(current_time);
+    lock.WaitMicros(next_sample);
+  }
+}
+
+
+}  // namespace dart
+
+#endif  // defined(TARGET_OS_ANDROID)