Profiler Take 2

runtime/vm/thread_interrupter.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 <cstdio>

[siva, 2013/12/11 02:52:21]

what is this?

We don't include c++ header files normally.

[Cutch, 2013/12/11 17:44:56]

Done.

+
+#include "vm/thread_interrupter.h"
+
+namespace dart {
+
+// Notes:
+//
+// The ThreadInterrupter interrupts all registered threads once per
+// interrupt period (default is every millisecond). While the thread is
+// interrupted, the thread's interrupt callback is invoked. Callbacks cannot
+// rely on being executed on the interrupted thread.
+//
+// There are two mechanisms used to interrupt a thread. The first, used on OSs
+// with pthreads (Android, Linux, and Mac), is thread specific signal delivery.
+// The second, used on Windows, is explicit suspend and resume thread system
+// calls. Signal delivery forbids taking locks and allocating memory (which
+// takes a lock). Explicit suspend and resume means that the interrupt callback
+// will not be executing on the interrupted thread, making it meaningless to
+// access TLS from within the thread interrupt callback. Combining these
+// limitations, thread interrupt callbacks are forbidden from:
+//
+//   * Accessing TLS.
+//   * Allocating memory.
+//   * Taking a lock.
+//
+// The ThreadInterrupter has a single monitor (monitor_). This monitor guards
+// access to the list of threads registered to receive interrupts (threads_).
+//
+// A thread can only register and unregister itself. Each thread has a heap
+// allocated ThreadState. A thread's ThreadState is lazily allocated the first
+// time the thread is registered. A pointer to a thread's ThreadState is stored
+// in the list of threads registered to receive interrupts (threads_) and in
+// thread local storage. When a thread's ThreadState is being modified, the
+// thread local storage pointer is temporarily set to NULL while the
+// modification is occurring. After the ThreadState has been updated, the
+// thread local storage pointer is set again. This has an important side
+// effect: if the thread is interrupted by a signal handler during a ThreadState
+// update the signal handler will immediately return.
+
+DEFINE_FLAG(bool, thread_interrupter, true, "Enable thread interrupter");
+DEFINE_FLAG(bool, trace_thread_interrupter, false,
+            "Trace thread interrupter");
+
+bool ThreadInterrupter::initialized_ = false;
+bool ThreadInterrupter::shutdown_ = false;
+bool ThreadInterrupter::thread_running_ = false;
+ThreadId ThreadInterrupter::interrupter_thread_id_ = Thread::kInvalidThreadId;
+Monitor* ThreadInterrupter::monitor_ = NULL;
+Monitor* ThreadInterrupter::start_stop_monitor_ = NULL;
+intptr_t ThreadInterrupter::interrupt_period_ = 1000;
+ThreadLocalKey ThreadInterrupter::thread_state_key_ =
+    Thread::kUnsetThreadLocalKey;
+ThreadInterrupter::ThreadState** ThreadInterrupter::threads_ = NULL;
+intptr_t ThreadInterrupter::threads_capacity_ = 0;
+intptr_t ThreadInterrupter::threads_size_ = 0;
+
+
+void ThreadInterrupter::InitOnce() {
+  if (!FLAG_thread_interrupter) {
+    return;
+  }
+  ASSERT(!initialized_);
+  initialized_ = true;
+  ASSERT(thread_state_key_ == Thread::kUnsetThreadLocalKey);
+  thread_state_key_ = Thread::CreateThreadLocal();
+  ASSERT(thread_state_key_ != Thread::kUnsetThreadLocalKey);
+  monitor_ = new Monitor();
+  start_stop_monitor_ = new Monitor();
+  ResizeThreads(16);
+  if (FLAG_trace_thread_interrupter) {
+    OS::Print("ThreadInterrupter starting up.\n");
+  }
+  ASSERT(interrupter_thread_id_ == Thread::kInvalidThreadId);
+  {
+    MonitorLocker startup_ml(start_stop_monitor_);
+    Thread::Start(ThreadMain, 0);
+    while (!thread_running_) {
+      startup_ml.Wait();
+    }
+  }
+  ASSERT(interrupter_thread_id_ != Thread::kInvalidThreadId);
+  if (FLAG_trace_thread_interrupter) {
+    OS::Print("ThreadInterrupter running.\n");
+  }
+}
+
+
+void ThreadInterrupter::Shutdown() {
+  if (!FLAG_thread_interrupter) {
+    return;
+  }
+  ASSERT(initialized_);
+  if (FLAG_trace_thread_interrupter) {
+    OS::Print("ThreadInterrupter shutting down.\n");
+  }
+  intptr_t size_at_shutdown = 0;
+  {
+    MonitorLocker ml(monitor_);
+    shutdown_ = true;
+    size_at_shutdown = threads_size_;
+    threads_size_ = 0;
+    threads_capacity_ = 0;
+    free(threads_);
+    threads_ = NULL;
+    ml.Notify();
+  }
+  {
+    MonitorLocker shutdown_ml(start_stop_monitor_);
+    while (thread_running_) {
+      shutdown_ml.Wait();
+    }
+  }
+  if (FLAG_trace_thread_interrupter) {
+    OS::Print("ThreadInterrupter shut down (%" Pd ").\n", size_at_shutdown);
+  }
+}
+
+// Delay between interrupts.
+void ThreadInterrupter::SetInterruptPeriod(intptr_t period) {
+  if (!FLAG_thread_interrupter) {
+    return;
+  }
+  ASSERT(period > 0);
+  {
+    MonitorLocker ml(monitor_);
+    interrupt_period_ = period;
+  }
+}
+
+
+// Register the currently running thread for interrupts. If the current thread
+// is already registered, callback and data will be updated.
+void ThreadInterrupter::Register(ThreadInterruptCallback callback, void* data) {
+  if (!FLAG_thread_interrupter) {
+    return;
+  }
+  ThreadId current_thread = Thread::GetCurrentThreadId();
+  ASSERT(!Thread::Compare(current_thread, interrupter_thread_id_));
+  {
+    MonitorLocker ml(monitor_);
+    // Set callback and data.
+    UpdateStateObject(callback, data);
+
+    intptr_t i = FindThreadIndex(current_thread);
+    if (i >= 0) {
+      return;
+    }
+    AddThread(current_thread, callback, data);
+    if (FLAG_trace_thread_interrupter) {
+      intptr_t tid = Thread::ThreadIdToIntPtr(current_thread);
+      OS::Print("ThreadInterrupter Added %p\n", reinterpret_cast<void*>(tid));
+    }
+    ml.Notify();

[siva, 2013/12/11 02:52:21]

Why is this notify needed? The next wake up of the interrupt thread will pick up
this isolate right?

[Cutch, 2013/12/11 17:44:56]

The notify is there in case we switch the thread to a more sophisticated
scheduling loop.

+  }
+}
+
+
+// Unregister the currently running thread for interrupts.
+void ThreadInterrupter::Unregister() {
+  if (!FLAG_thread_interrupter) {
+    return;
+  }
+  ThreadId current_thread = Thread::GetCurrentThreadId();
+  ASSERT(!Thread::Compare(current_thread, interrupter_thread_id_));
+  {
+    MonitorLocker ml(monitor_);
+    // Clear callback and data.
+    UpdateStateObject(NULL, NULL);
+
+    intptr_t index = FindThreadIndex(current_thread);
+    if (index < 0) {
+      // Not registered.
+      return;
+    }
+    ThreadState* state = RemoveThread(index);
+    ASSERT(state != NULL);
+    ASSERT(state == ThreadInterrupter::CurrentThreadState());
+    if (FLAG_trace_thread_interrupter) {
+      intptr_t tid = Thread::ThreadIdToIntPtr(current_thread);
+      OS::Print("ThreadInterrupter Removed %p\n", reinterpret_cast<void*>(tid));
+    }
+    ml.Notify();

[siva, 2013/12/11 02:52:21]

Ditto comment about this Notify.

+  }
+}
+
+
+void ThreadInterrupter::UpdateStateObject(ThreadInterruptCallback callback,
+                                          void* data) {
+  ThreadState* state = CurrentThreadState();
+  ThreadId current_thread = Thread::GetCurrentThreadId();
+  if (state == NULL) {
+    // Create thread state object lazily.
+    if (FLAG_trace_thread_interrupter) {
+      intptr_t tid = Thread::ThreadIdToIntPtr(current_thread);
+      OS::Print("ThreadInterrupter Tracking %p\n",
+                reinterpret_cast<void*>(tid));
+    }
+    state = new ThreadState();
+    state->id = current_thread;
+    SetCurrentThreadState(state);
+  }
+  ASSERT(state != NULL);
+  ASSERT(Thread::Compare(state->id, Thread::GetCurrentThreadId()));
+  SetCurrentThreadState(NULL);
+  // It is now safe to modify the state object. If an interrupt occurs,
+  // the current thread state will be NULL.
+  state->callback = callback;
+  state->data = data;
+  SetCurrentThreadState(state);
+  if (FLAG_trace_thread_interrupter) {
+    intptr_t tid = Thread::ThreadIdToIntPtr(current_thread);
+    if (callback == NULL) {
+      OS::Print("ThreadInterrupter Cleared %p\n", reinterpret_cast<void*>(tid));
+    } else {
+      OS::Print("ThreadInterrupter Updated %p\n", reinterpret_cast<void*>(tid));
+    }
+  }
+}
+
+
+ThreadInterrupter::ThreadState* ThreadInterrupter::CurrentThreadState() {
+  return reinterpret_cast<ThreadState*>(
+      Thread::GetThreadLocal(thread_state_key_));
+}
+
+
+void ThreadInterrupter::SetCurrentThreadState(ThreadState* state) {
+  Thread::SetThreadLocal(thread_state_key_, reinterpret_cast<uword>(state));
+}
+
+
+void ThreadInterrupter::ResizeThreads(intptr_t new_capacity) {

[siva, 2013/12/11 02:52:21]

// Must be called with monitor_ locked.

[Cutch, 2013/12/11 17:44:56]

Done.

+  ASSERT(new_capacity < kMaxThreads);
+  ASSERT(new_capacity > threads_capacity_);
+  ThreadState* state = NULL;
+  threads_ = reinterpret_cast<ThreadState**>(
+      realloc(threads_, sizeof(state) * new_capacity));
+  for (intptr_t i = threads_capacity_; i < new_capacity; i++) {
+    threads_[i] = NULL;
+  }
+  threads_capacity_ = new_capacity;
+}
+
+
+void ThreadInterrupter::AddThread(ThreadId id, ThreadInterruptCallback callback,
+                                  void* data) {
+  // Must be called with monitor_ locked.
+  if (threads_ == NULL) {
+    // We are shutting down.
+    return;
+  }
+  if (threads_size_ == threads_capacity_) {
+    ResizeThreads(threads_capacity_ == 0 ? 16 : threads_capacity_ * 2);
+  }
+  UpdateStateObject(callback, data);
+  ThreadState* state = CurrentThreadState();
+  ASSERT(state != NULL);
+  threads_[threads_size_] = state;
+  threads_size_++;
+}
+
+
+intptr_t ThreadInterrupter::FindThreadIndex(ThreadId id) {
+  // Must be called with monitor_ locked.
+  if (threads_ == NULL) {
+    // We are shutting down.
+    return -1;
+  }
+  for (intptr_t i = 0; i < threads_size_; i++) {
+    if (threads_[i]->id == id) {
+      return i;
+    }
+  }
+  return -1;
+}
+
+
+ThreadInterrupter::ThreadState* ThreadInterrupter::RemoveThread(intptr_t i) {
+  // Must be called with monitor_ locked.
+  if (threads_ == NULL) {
+    // We are shutting down.
+    return NULL;
+  }
+  ASSERT(i < threads_size_);
+  ThreadState* state = threads_[i];
+  ASSERT(state != NULL);
+  intptr_t last = threads_size_ - 1;
+  if (i != last) {
+    threads_[i] = threads_[last];
+  }
+  // Mark last as NULL.
+  threads_[last] = NULL;
+  // Pop.
+  threads_size_--;
+  return state;
+}
+
+
+void ThreadInterruptNoOp(const InterruptedThreadState& state, void* data) {
+  // NoOp.
+}
+
+}  // namespace dart