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

examples/indirect_service/indirect_service_demo.cc

Index: examples/indirect_service/indirect_service_demo.cc
diff --git a/examples/indirect_service/indirect_service_demo.cc b/examples/indirect_service/indirect_service_demo.cc
new file mode 100644
index 0000000000000000000000000000000000000000..a11d3e5adbedaf93c682201785aa44235eb052fa
--- /dev/null
+++ b/examples/indirect_service/indirect_service_demo.cc
@@ -0,0 +1,148 @@
+// 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/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) {
+    thread_.Start();

[qsr, 2014/11/20 08:49:10]

You might want to put a MessagePumpMojo on this thread, otherwise async wait are
using thread hops.

[hansmuller, 2014/11/20 17:53:04]

I've just tried that.

    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));

It causes the app to SEGV upon ApplicationImpl::Terminate(). The focus of this
demo is really interface vs interface&, so leaving this optimization out seems
OK to me. It sleeps to increase thread overlap after all :-).

+    thread_.message_loop()->PostTask(
+          FROM_HERE, base::Bind(&DemoTask::Run, base::Unretained(this)));

[yzshen1, 2014/11/20 18:17:17]

wrong indent.

[hansmuller, 2014/11/20 19:27:59]

Done.

+  }
+
+  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.
+      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_);
+  }
+
+  ScopedMessagePipeHandle proxy_handle_;
+  base::Thread thread_;
+  IntegerServicePtr integer_service_;

[yzshen1, 2014/11/20 18:17:18]

This needs to be destroyed on |thread_|.

+  DemoTaskFinishedCallback finished_callback_;
+  unsigned iteration_count_;
+  std::vector<int32_t> results_;
+};
+
+// Connect to the IntegerService and give its proxy to the
+// IndirectIntegerService. Start task_count_ 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 task_iteration_count times, collect the results in

[yzshen1, 2014/11/20 18:17:17]

task_iteration_count_

[hansmuller, 2014/11/20 19:27:59]

Done.

+// a vector and return them to FinishDemoTask.
+//
+// The IntegerService, whose value is initially 0, will be called a total of
+// N = |task_count_ * task_iteration_count_| 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 digit appears in each column provies that things

[Aaron Boodman, 2014/11/20 07:21:58]

This sentence doesn't parse. Missing the word 'one'?

[hansmuller, 2014/11/20 17:53:04]

And "provies".  Yikes.

[hansmuller, 2014/11/20 17:53:04]

Yes, thanks for reading all of this.

+// are working correctly.
+

[Aaron Boodman, 2014/11/20 07:21:58]

No empty line necessary.

[hansmuller, 2014/11/20 17:53:04]

Done.

+class IndirectServiceDemoAppDelegate : public ApplicationDelegate {
+ public:
+  virtual void Initialize(ApplicationImpl* app) override {
+    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 < task_count_; 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, to
+      // use its MessagePipe.
+      tasks_.push_back(new DemoTask(integer_service.PassMessagePipe(),

[yzshen1, 2014/11/20 18:17:17]

Who owns these DemoTask instances?

+                                    finished_callback,
+                                    task_iteration_count_));
+    }
+  }
+
+ private:
+  const unsigned task_count_ = 10;

[yzshen1, 2014/11/20 18:17:17]

Maybe consider "static const" and name them kTaskCount and kTaskIterationCount.

[hansmuller, 2014/11/20 19:27:59]

Done.

+  const unsigned task_iteration_count_ = 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(task_count_ * task_iteration_count_, ' ');
+    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<DemoTask*> tasks_;
+};
+
+
+}  // namespace examples
+}  // namespace mojo
+
+MojoResult MojoMain(MojoHandle shell_handle) {
+  mojo::ApplicationRunnerChromium runner(
+      new mojo::examples::IndirectServiceDemoAppDelegate);
+  return runner.Run(shell_handle);
+}