Mojo Example that demos the difference between providing and requesting an interface

examples/indirect_service/indirect_service_demo.cc

+// Copyright 2014 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 <cstdlib>
+
+#include "base/bind.h"
+#include "base/memory/scoped_vector.h"
+#include "base/message_loop/message_loop.h"
+#include "base/threading/thread.h"
+#include "base/time/time.h"
+#include "examples/indirect_service/indirect_service_demo.mojom.h"
+#include "mojo/application/application_runner_chromium.h"
+#include "mojo/common/message_pump_mojo.h"
+#include "mojo/public/c/system/main.h"
+#include "mojo/public/cpp/application/application_delegate.h"
+#include "mojo/public/cpp/application/application_impl.h"
+
+namespace mojo {
+namespace examples {
+
+class DemoTask;
+
+typedef typename base::Callback<void(DemoTask*, const std::vector<int32_t>&)>
+    DemoTaskFinishedCallback;
+
+// A thread that connects to the IndirectIntegerService, gets a connection
+// to its IntegerService, and then calls Increment() iteration_count times.
+// The results are saved and returned with the finished_callback.
+class DemoTask {
+ public:
+  DemoTask(ScopedMessagePipeHandle proxy_handle,
+           const DemoTaskFinishedCallback& finished_callback,
+           unsigned iteration_count)
+    : proxy_handle_(proxy_handle.Pass()),
+      thread_("DemoTask"),
+      finished_callback_(finished_callback),
+      iteration_count_(iteration_count) {
+

[yzshen1, 2014/11/20 22:01:44]

unnecessary empty line.

+    base::Thread::Options options;
+    options.message_loop_type = base::MessageLoop::TYPE_CUSTOM;
+    options.message_pump_factory = base::Bind(&common::MessagePumpMojo::Create);
+    CHECK(thread_.StartWithOptions(options));
+
+    thread_.message_loop()->PostTask(
+        FROM_HERE, base::Bind(&DemoTask::Run, base::Unretained(this)));
+  }
+
+  void Run() {
+    integer_service_.Bind(proxy_handle_.Pass());
+    base::Callback<void(int32_t)> callback =
+        base::Bind(&DemoTask::SaveResultAndFinish, base::Unretained(this));
+    for(int unsigned i = 0; i < iteration_count_; i++) {
+      integer_service_->Increment(callback);
+      // To ensure that the DemoTask threads' execution overlaps, sleep.
+      if (i < iteration_count_ - 1)
+        base::PlatformThread::Sleep(
+            base::TimeDelta::FromMilliseconds(rand() % 10));
+    }
+  }
+
+ private:
+  void SaveResultAndFinish(int32_t result) {
+    results_.push_back(result);
+    if (results_.size() == iteration_count_) {
+      finished_callback_.Run(this, results_);
+      integer_service_.reset(); // Must be done on thread_.

[yzshen1, 2014/11/20 22:01:44]

It seems better to do the reset before running the callback. Although it is not
an issue in the current scenario, theoretically finished_callback_ could destroy
this object synchronously.

[hansmuller, 2014/11/20 22:35:38]

Good point.

+    }
+  }
+
+  ScopedMessagePipeHandle proxy_handle_;
+  base::Thread thread_;
+  IntegerServicePtr integer_service_;
+  DemoTaskFinishedCallback finished_callback_;
+  unsigned iteration_count_;
+  std::vector<int32_t> results_;
+};
+
+// Connect to the IntegerService and give its proxy to the
+// IndirectIntegerService. Start kTaskCount DemoTask threads all of
+// which will use the IndirectIntegerService to get their own connection
+// to the (one) IntegerService. Each DemoTask will call the IntegerService's
+// Increment() method kTaskIterationCount times, collect the results in
+// a vector and return them to FinishDemoTask.
+//
+// The IntegerService, whose value is initially 0, will be called a total of
+// N = |kTaskCount * kTaskIterationCount| times. Each DemoTask's results
+// are displayed in array of length N. Digits appear in positions that
+// correspond to the results obtained by the DemoTask thread. The results
+// show that the DemoTask threads are accessing the Integer in parallel.
+// The fact that only one digit appears in each column shows that things
+// are working correctly.
+class IndirectServiceDemoAppDelegate : public ApplicationDelegate {
+ public:
+  virtual void Initialize(ApplicationImpl* app) override {

[yzshen1, 2014/11/20 22:01:44]

nit: no need to have virtual

[hansmuller, 2014/11/20 22:35:38]

Sorry, I missed that one.

+    IntegerServicePtr indirect_service_delegate;
+    app->ConnectToService("mojo:indirect_integer_service",
+        &indirect_integer_service_);
+    app->ConnectToService("mojo:integer_service", &indirect_service_delegate);
+    indirect_integer_service_->Set(indirect_service_delegate.Pass());
+
+    for (unsigned i = 0; i < kTaskCount; i++) {
+      IntegerServicePtr integer_service;
+      indirect_integer_service_->Get(GetProxy(&integer_service));
+      DemoTaskFinishedCallback finished_callback = base::Bind(
+          &IndirectServiceDemoAppDelegate::FinishDemoTask,
+          base::Unretained(this),
+          base::Unretained(base::MessageLoop::current()));
+      // We're passing the integer_service_ proxy to another thread, so
+      // use its MessagePipe.
+      scoped_ptr<DemoTask> task(new DemoTask(integer_service.PassMessagePipe(),
+                                             finished_callback,
+                                             kTaskIterationCount));
+      tasks_.push_back(task.Pass());
+    }
+  }
+
+ private:
+  static const unsigned kTaskCount = 10;
+  static const unsigned kTaskIterationCount = 6;
+
+  // This method is called on a DemoTask thread. It just calls DoFinishDemoTask
+  // on the application's run loop. Doing so serializes the DoFinishDemoTask
+  // calls.
+  void FinishDemoTask(base::MessageLoop *run_loop,
+                      DemoTask* task,
+                      const std::vector<int32_t>& results) {
+    run_loop->PostTask(FROM_HERE, base::Bind(
+        &IndirectServiceDemoAppDelegate::DoFinishDemoTask,
+        base::Unretained(this),
+        base::Unretained(task),
+        results));
+  }
+
+  void DoFinishDemoTask(DemoTask* task, const std::vector<int32_t>& results) {
+    std::string display(kTaskCount * kTaskIterationCount, ' ');
+    for (unsigned i = 0; i < results.size(); i++)
+      display[results[i]] = '0' + (results[i] % 10);
+    printf("DemoTask Thread [%s]\n", display.c_str());
+    tasks_.erase(std::remove(tasks_.begin(), tasks_.end(), task), tasks_.end());
+    if (tasks_.empty())
+      ApplicationImpl::Terminate();
+  }
+
+  IndirectIntegerServicePtr indirect_integer_service_;
+  std::vector<scoped_ptr<DemoTask>> tasks_;

[yzshen1, 2014/11/20 22:01:44]

This is a library feature of C++11 (move-only objects in std::vector). I don't
think we are allowed to use it.

[hansmuller, 2014/11/20 22:35:38]

OK.

+};
+
+
+}  // namespace examples
+}  // namespace mojo
+
+MojoResult MojoMain(MojoHandle shell_handle) {
+  mojo::ApplicationRunnerChromium runner(
+      new mojo::examples::IndirectServiceDemoAppDelegate);
+  return runner.Run(shell_handle);
+}