Gather trace data by waiting on handles with a fixed timeout

services/tracing/tracing_app.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "services/tracing/tracing_app.h"
+
+#include "base/bind.h"
+#include "base/logging.h"
+#include "base/message_loop/message_loop.h"
+
+namespace tracing {
+
+TracingApp::TracingApp() : coordinator_binding_(this) {
+}
+
+TracingApp::~TracingApp() {
+}
+
+bool TracingApp::ConfigureIncomingConnection(
+    mojo::ApplicationConnection* connection) {
+  connection->AddService<TraceCoordinator>(this);
+
+  // If someone connects to us they may want to use the TraceCoordinator
+  // interface and/or they may want to expose themselves to be traced. Attempt
+  // to connect to the TraceController interface to see if the application
+  // connecting to us wants to be traced. They can refuse the connection or
+  // close the pipe if not.
+  TraceControllerPtr controller_ptr;
+  connection->ConnectToService(&controller_ptr);
+  if (tracing_active_) {
+    TraceDataCollectorPtr collector_ptr;
+    collector_impls_.push_back(
+        new CollectorImpl(GetProxy(&collector_ptr), sink_.get()));
+    controller_ptr->StartTracing(tracing_categories_, collector_ptr.Pass());
+  }
+  controller_ptrs_.AddInterfacePtr(controller_ptr.Pass());
+  return true;
+}
+
+// mojo::InterfaceFactory<TraceCoordinator> implementation.
+void TracingApp::Create(mojo::ApplicationConnection* connection,
+                        mojo::InterfaceRequest<TraceCoordinator> request) {
+  coordinator_binding_.Bind(request.Pass());
+}
+
+// tracing::TraceCoordinator implementation.
+void TracingApp::Start(mojo::ScopedDataPipeProducerHandle stream,
+                       const mojo::String& categories) {
+  tracing_categories_ = categories;
+  sink_.reset(new TraceDataSink(stream.Pass()));
+  controller_ptrs_.ForAllPtrs([categories, this](TraceController* controller) {
+    TraceDataCollectorPtr ptr;
+    collector_impls_.push_back(new CollectorImpl(GetProxy(&ptr), sink_.get()));
+    controller->StartTracing(categories, ptr.Pass());
+  });
+  tracing_active_ = true;
+}
+
+void TracingApp::StopAndFlush() {
+  tracing_active_ = false;
+  controller_ptrs_.ForAllPtrs(
+      [](TraceController* controller) { controller->StopTracing(); });
+
+  // Sending the StopTracing message to registered controllers will request that
+  // they send trace data back via the collector interface and, when they are
+  // done, close the collector pipe. We don't know how long they will take. We
+  // want to read all data that any collector might send until all collectors or
+  // closed or an (arbitrary) deadline has passed. Since the bindings don't
+  // support this directly we do our own MojoWaitMany over the handles and read
+  // individual messages until all are closed or our absolute deadline has
+  // elapsed.
+  static const MojoDeadline kTimeToWaitMicros = 100 * 1000;
+  MojoTimeTicks end = MojoGetTimeTicksNow() + kTimeToWaitMicros;
+
+  while (!collector_impls_.empty()) {
+    MojoTimeTicks now = MojoGetTimeTicksNow();
+    if (now >= end)  // Timed out?
+      break;
+
+    MojoDeadline mojo_deadline = end - now;
+    std::vector<mojo::Handle> handles;
+    std::vector<MojoHandleSignals> signals;
+    for (const auto& it : collector_impls_) {
+      handles.push_back(it->TraceDataCollectorHandle());
+      signals.push_back(MOJO_HANDLE_SIGNAL_READABLE |
+                        MOJO_HANDLE_SIGNAL_PEER_CLOSED);
+    }
+    std::vector<MojoHandleSignalsState> signals_states(signals.size());
+    const mojo::WaitManyResult wait_many_result =
+        mojo::WaitMany(handles, signals, mojo_deadline, &signals_states);
+    if (wait_many_result.result == MOJO_RESULT_DEADLINE_EXCEEDED) {
+      // Timed out waiting, nothing more to read.
+      break;
+    }
+    if (wait_many_result.IsIndexValid()) {
+      // Iterate backwards so we can remove closed pipes from |collector_impls_|
+      // without invalidating subsequent offsets.
+      for (size_t i = signals_states.size(); i != 0; --i) {
+        size_t index = i - 1;
+        MojoHandleSignals satisfied = signals_states[index].satisfied_signals;
+        if (satisfied & MOJO_HANDLE_SIGNAL_READABLE)
+          collector_impls_[index]->TryRead();
+        if (satisfied & MOJO_HANDLE_SIGNAL_PEER_CLOSED)
+          collector_impls_.erase(collector_impls_.begin() + index);
+      }
+    }
+  }
+  AllDataCollected();
+}
+
+void TracingApp::AllDataCollected() {
+  collector_impls_.clear();
+  sink_->Flush();
+}
+
+}  // namespace tracing