Web MIDI: add dynamic MidiManager instantiation support for Linux

media/midi/midi_service.cc

Index: media/midi/midi_service.cc
diff --git a/media/midi/midi_service.cc b/media/midi/midi_service.cc
index 0d0112459a8c65939aa85a79ae81db5b80fd5129..a523ae4ff52df0775fb0cab587baf39076a65ded 100644
--- a/media/midi/midi_service.cc
+++ b/media/midi/midi_service.cc
@@ -4,36 +4,88 @@
 
 #include "media/midi/midi_service.h"
 
+#include "base/feature_list.h"
+#include "base/memory/ptr_util.h"
+#include "base/strings/stringprintf.h"
 #include "media/midi/midi_manager.h"
+#include "media/midi/midi_switches.h"
 
 namespace midi {
 
+namespace {
+
+// TODO(toyoshim): Support on all platforms. See https://crbug.com/672793.
+#if defined(OS_LINUX)
+constexpr bool kIsDynamicInstantiationSupported = true;
+#else
+constexpr bool kIsDynamicInstantiationSupported = false;
+#endif
+
+MidiService* g_midi_service = nullptr;
+
+}  // namespace
+
 MidiService::MidiService(std::unique_ptr<MidiManager> manager) {
   base::AutoLock lock(lock_);
-  if (manager.get())
+
+  CHECK(!g_midi_service);
+  g_midi_service = this;
+
+  is_dynamic_instantiation_enabled_ = false;
+  active_clients_ = 0u;
+  if (manager.get()) {
     manager_ = std::move(manager);
-  else
-    manager_.reset(MidiManager::Create());
+  } else if (kIsDynamicInstantiationSupported &&
+             base::FeatureList::IsEnabled(
+                 features::kMidiManagerDynamicInstantiation)) {
+    is_dynamic_instantiation_enabled_ = true;
+  } else {
+    manager_ = base::WrapUnique(MidiManager::Create());
+  }
 }
 
 MidiService::~MidiService() {
   base::AutoLock lock(lock_);
+
   manager_.reset();
+
+  CHECK(g_midi_service);
+  g_midi_service = nullptr;
+
+  base::AutoLock threads_lock(threads_lock_);
+  threads_.clear();
 }
 
 void MidiService::Shutdown() {
   base::AutoLock lock(lock_);
-  manager_->Shutdown();
+  if (manager_.get())
+    manager_->Shutdown();
 }
 
 void MidiService::StartSession(MidiManagerClient* client) {
   base::AutoLock lock(lock_);
+  if (!manager_.get()) {
+    CHECK(is_dynamic_instantiation_enabled_);
+    CHECK_EQ(0u, active_clients_);
+    manager_.reset(MidiManager::Create());
+  }
+  active_clients_++;
   manager_->StartSession(client);
 }
 
 void MidiService::EndSession(MidiManagerClient* client) {
   base::AutoLock lock(lock_);
+  CHECK(manager_.get());
+  CHECK_NE(0u, active_clients_);
   manager_->EndSession(client);
+  active_clients_--;
+  if (is_dynamic_instantiation_enabled_ && !active_clients_) {
+    // MidiManager for each platform should be able to shutdown correctly even
+    // if following Shutdown() call happens in the middle of
+    // StartInitialization() to support the dynamic instantiation feature.
+    manager_->Shutdown();
+    manager_.reset();
+  }
 }
 
 void MidiService::DispatchSendMidiData(MidiManagerClient* client,
@@ -44,4 +96,24 @@ void MidiService::DispatchSendMidiData(MidiManagerClient* client,
   manager_->DispatchSendMidiData(client, port_index, data, timestamp);
 }
 
+// static
+scoped_refptr<base::SingleThreadTaskRunner> MidiService::GetTaskRunner(
+    size_t runner_id) {
+  // MidiService outlives MidiManager that could call GetTaskRunner().
+  return g_midi_service->GetTaskRunnerImpl(runner_id);

[yhirano, 2017/02/08 03:50:24]

Is it possible to store a MidiService pointer in MidiManagerAlsa (assuming
MidiService always outlives MidiManager)? With that we don't need g_midi_service
which I don't like.

+}
+
+scoped_refptr<base::SingleThreadTaskRunner> MidiService::GetTaskRunnerImpl(
+    size_t runner_id) {
+  base::AutoLock lock(threads_lock_);
+  if (threads_.size() <= runner_id)
+    threads_.resize(runner_id + 1);
+  if (!threads_[runner_id].get()) {
+    threads_[runner_id] = base::MakeUnique<base::Thread>(
+        base::StringPrintf("MidiServiceThread(%zu)", runner_id));
+    threads_[runner_id]->Start();
+  }
+  return threads_[runner_id]->task_runner();
+}
+
 }  // namespace midi