Revert of Mojo: Armed Watchers

content/common/message_port.cc

Index: content/common/message_port.cc
diff --git a/content/common/message_port.cc b/content/common/message_port.cc
index 428162eb8a489da988d5e5f41b8861ca525def08..c89d7b5a0d0cc313290329602fedc13e6dff9150 100644
--- a/content/common/message_port.cc
+++ b/content/common/message_port.cc
@@ -4,9 +4,7 @@
 
 #include "content/common/message_port.h"
 
-#include "base/bind.h"
 #include "base/logging.h"
-#include "base/threading/thread_task_runner_handle.h"
 
 namespace content {
 
@@ -149,86 +147,40 @@
   if (!callback_)
     return;
 
-  DCHECK(!watcher_handle_.is_valid());
-  MojoResult rv = CreateWatcher(&State::CallOnHandleReady, &watcher_handle_);
-  DCHECK_EQ(MOJO_RESULT_OK, rv);
-
-  // We use a scoped_refptr<State> instance as the watch context. This is owned
-  // by the watch and deleted upon receiving a cancellation notification.
-  scoped_refptr<State>* state_ref = new scoped_refptr<State>(this);
-  context_ = reinterpret_cast<uintptr_t>(state_ref);
-
   // NOTE: An HTML MessagePort does not receive an event to tell it when the
   // peer has gone away, so we only watch for readability here.
-  rv = MojoWatch(watcher_handle_.get().value(), handle_.get().value(),
-                 MOJO_HANDLE_SIGNAL_READABLE, context_);
-  DCHECK_EQ(MOJO_RESULT_OK, rv);
-
-  ArmWatcher();
+  MojoResult rv = MojoWatch(handle_.get().value(),
+                            MOJO_HANDLE_SIGNAL_READABLE,
+                            &MessagePort::State::OnHandleReady,
+                            reinterpret_cast<uintptr_t>(this));
+  if (rv != MOJO_RESULT_OK)
+    DVLOG(1) << this << " MojoWatch failed: " << rv;
 }
 
 void MessagePort::State::CancelWatch() {
-  watcher_handle_.reset();
-  context_ = 0;
+  if (!callback_)
+    return;
+
+  // NOTE: This synchronizes with the thread where OnHandleReady runs so we are
+  // sure to not be racing with it.
+  MojoCancelWatch(handle_.get().value(), reinterpret_cast<uintptr_t>(this));
 }
 
-MessagePort::State::~State() = default;
-
-void MessagePort::State::ArmWatcher() {
-  if (!watcher_handle_.is_valid())
-    return;
-
-  uint32_t num_ready_contexts = 1;
-  uintptr_t ready_context;
-  MojoResult ready_result;
-  MojoHandleSignalsState ready_state;
-  MojoResult rv =
-      MojoArmWatcher(watcher_handle_.get().value(), &num_ready_contexts,
-                     &ready_context, &ready_result, &ready_state);
-  if (rv == MOJO_RESULT_OK)
-    return;
-
-  // The watcher could not be armed because it would notify immediately.
-  DCHECK_EQ(MOJO_RESULT_FAILED_PRECONDITION, rv);
-  DCHECK_EQ(1u, num_ready_contexts);
-  DCHECK_EQ(context_, ready_context);
-
-  if (ready_result == MOJO_RESULT_OK) {
-    // The handle is already signaled, so we trigger a callback now.
-    base::ThreadTaskRunnerHandle::Get()->PostTask(
-        FROM_HERE, base::Bind(&State::OnHandleReady, this, MOJO_RESULT_OK));
-    return;
-  }
-
-  if (ready_result == MOJO_RESULT_FAILED_PRECONDITION) {
-    DVLOG(1) << this << " MojoArmWatcher failed because of a broken pipe.";
-    return;
-  }
-
-  NOTREACHED();
-}
-
-void MessagePort::State::OnHandleReady(MojoResult result) {
-  if (result == MOJO_RESULT_OK && callback_) {
-    callback_.Run();
-    ArmWatcher();
+// static
+void MessagePort::State::OnHandleReady(
+    uintptr_t context,
+    MojoResult result,
+    MojoHandleSignalsState signals_state,
+    MojoWatchNotificationFlags flags) {
+  if (result == MOJO_RESULT_OK) {
+    reinterpret_cast<MessagePort::State*>(context)->callback_.Run();
   } else {
     // And now his watch is ended.
   }
 }
 
-// static
-void MessagePort::State::CallOnHandleReady(uintptr_t context,
-                                           MojoResult result,
-                                           MojoHandleSignalsState signals_state,
-                                           MojoWatcherNotificationFlags flags) {
-  auto* state_ref = reinterpret_cast<scoped_refptr<State>*>(context);
-  if (result == MOJO_RESULT_CANCELLED) {
-    // Last notification. Delete the watch's owned State ref.
-    delete state_ref;
-  } else {
-    (*state_ref)->OnHandleReady(result);
-  }
+MessagePort::State::~State() {
+  CancelWatch();
 }
 
 }  // namespace content