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// 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 "mojo/edk/system/channel_endpoint.h"
#include "base/logging.h"
#include "base/threading/platform_thread.h"
#include "mojo/edk/system/channel.h"
#include "mojo/edk/system/channel_endpoint_client.h"
namespace mojo {
namespace system {
ChannelEndpoint::ChannelEndpoint(ChannelEndpointClient* client,
unsigned client_port,
MessageInTransitQueue* message_queue)
: client_(client),
client_port_(client_port),
channel_(nullptr),
is_detached_from_channel_(false) {
DCHECK(client_ || message_queue);
if (message_queue)
channel_message_queue_.Swap(message_queue);
}
bool ChannelEndpoint::EnqueueMessage(scoped_ptr<MessageInTransit> message) {
DCHECK(message);
base::AutoLock locker(lock_);
if (!channel_) {
// We may reach here if we haven't been attached/run yet.
// TODO(vtl): We may also reach here if the channel is shut down early for
// some reason (with live message pipes on it). Ideally, we'd return false
// (and not enqueue the message), but we currently don't have a way to check
// this.
channel_message_queue_.AddMessage(message.Pass());
return true;
}
return WriteMessageNoLock(message.Pass());
}
bool ChannelEndpoint::ReplaceClient(ChannelEndpointClient* client,
unsigned client_port) {
DCHECK(client);
base::AutoLock locker(lock_);
DCHECK(client_);
DCHECK(client != client_.get() || client_port != client_port_);
client_ = client;
client_port_ = client_port;
return !is_detached_from_channel_;
}
void ChannelEndpoint::DetachFromClient() {
base::AutoLock locker(lock_);
DCHECK(client_);
client_ = nullptr;
if (!channel_)
return;
channel_->DetachEndpoint(this, local_id_, remote_id_);
ResetChannelNoLock();
}
void ChannelEndpoint::AttachAndRun(Channel* channel,
ChannelEndpointId local_id,
ChannelEndpointId remote_id) {
DCHECK(channel);
DCHECK(local_id.is_valid());
DCHECK(remote_id.is_valid());
base::AutoLock locker(lock_);
DCHECK(!channel_);
DCHECK(!local_id_.is_valid());
DCHECK(!remote_id_.is_valid());
channel_ = channel;
local_id_ = local_id;
remote_id_ = remote_id;
while (!channel_message_queue_.IsEmpty()) {
LOG_IF(WARNING, !WriteMessageNoLock(channel_message_queue_.GetMessage()))
<< "Failed to write enqueue message to channel";
}
if (!client_) {
channel_->DetachEndpoint(this, local_id_, remote_id_);
ResetChannelNoLock();
}
}
void ChannelEndpoint::OnReadMessage(scoped_ptr<MessageInTransit> message) {
scoped_refptr<ChannelEndpointClient> client;
unsigned client_port = 0;
// This loop is to make |ReplaceClient()| work. We can't call the client's
// |OnReadMessage()| under our lock, so by the time we do that, |client| may
// no longer be our client.
//
// In that case, |client| must return false. We'll then yield, and retry with
// the new client. (Theoretically, the client could be replaced again.)
//
// This solution isn't terribly elegant, but it's the least costly way of
// handling/avoiding this (very unlikely) race. (Other solutions -- e.g.,
// adding a client message queue, which the client only fetches messages from
// -- impose significant cost in the common case.)
for (;;) {
{
base::AutoLock locker(lock_);
if (!channel_ || !client_) {
// This isn't a failure per se. (It just means that, e.g., the other end
// of the message point closed first.)
return;
}
// If we get here in a second (third, etc.) iteration of the loop, it's
// because |ReplaceClient()| was called.
DCHECK(client_ != client || client_port_ != client_port);
// Take a ref, and call |OnReadMessage()| outside the lock.
client = client_;
client_port = client_port_;
}
if (client->OnReadMessage(client_port, message.get())) {
ignore_result(message.release());
break;
}
base::PlatformThread::YieldCurrentThread();
}
}
void ChannelEndpoint::DetachFromChannel() {
scoped_refptr<ChannelEndpointClient> client;
unsigned client_port = 0;
{
base::AutoLock locker(lock_);
if (client_) {
// Take a ref, and call |OnDetachFromChannel()| outside the lock.
client = client_;
client_port = client_port_;
}
// |channel_| may already be null if we already detached from the channel in
// |DetachFromClient()| by calling |Channel::DetachEndpoint()| (and there
// are racing detaches).
if (channel_)
ResetChannelNoLock();
else
DCHECK(is_detached_from_channel_);
}
// If |ReplaceClient()| is called (from another thread) after the above locked
// section but before we call |OnDetachFromChannel()|, |ReplaceClient()|
// return false to notify the caller that the channel was already detached.
// (The old client has to accept the arguably-spurious call to
// |OnDetachFromChannel()|.)
if (client)
client->OnDetachFromChannel(client_port);
}
ChannelEndpoint::~ChannelEndpoint() {
DCHECK(!client_);
DCHECK(!channel_);
DCHECK(!local_id_.is_valid());
DCHECK(!remote_id_.is_valid());
}
bool ChannelEndpoint::WriteMessageNoLock(scoped_ptr<MessageInTransit> message) {
DCHECK(message);
lock_.AssertAcquired();
DCHECK(channel_);
DCHECK(local_id_.is_valid());
DCHECK(remote_id_.is_valid());
message->SerializeAndCloseDispatchers(channel_);
message->set_source_id(local_id_);
message->set_destination_id(remote_id_);
return channel_->WriteMessage(message.Pass());
}
void ChannelEndpoint::ResetChannelNoLock() {
DCHECK(channel_);
DCHECK(local_id_.is_valid());
DCHECK(remote_id_.is_valid());
DCHECK(!is_detached_from_channel_);
channel_ = nullptr;
local_id_ = ChannelEndpointId();
remote_id_ = ChannelEndpointId();
is_detached_from_channel_ = true;
}
} // namespace system
} // namespace mojo
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