Add support to be able to asynchronously read from a CancelableSyncSocket

media/audio/async_socket_io_handler_posix.cc

+// Copyright (c) 2012 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 "media/audio/async_socket_io_handler.h"
+
+#include <fcntl.h>
+#include "base/eintr_wrapper.h"
+
+namespace media {
+
+AsyncSocketIoHandler::AsyncSocketIoHandler()
+    : socket_(base::SyncSocket::kInvalidHandle),
+      is_watching_(false) {}
+
+AsyncSocketIoHandler::~AsyncSocketIoHandler() {
+  DCHECK(CalledOnValidThread());
+}
+
+void AsyncSocketIoHandler::OnFileCanReadWithoutBlocking(int socket) {
+  DCHECK(CalledOnValidThread());
+  DCHECK_EQ(socket, socket_);
+  if (!read_complete_.is_null()) {
+    int bytes_read = HANDLE_EINTR(read(socket_, pending_buffer_,
+                                       pending_buffer_len_));
+    DCHECK_GT(bytes_read, 0);
+    read_complete_.Run(bytes_read > 0 ? bytes_read : 0);
+    read_complete_.Reset();
+  } else {
+    // We're getting notifications that we can read from the socket while
+    // we're not waiting for data.  In order to not starve the message loop,
+    // let's stop watching the fd and restart the watch when Read() is called.
+    is_watching_ = false;
+    socket_watcher_.StopWatchingFileDescriptor();
+  }
+}
+
+bool AsyncSocketIoHandler::Read(char* buffer, int buffer_len,
+                                const ReadCompleteCallback& callback) {
+  DCHECK(CalledOnValidThread());
+  DCHECK(read_complete_.is_null());
+
+  EnsureWatchingSocket();
+
+  int bytes_read = HANDLE_EINTR(read(socket_, buffer, buffer_len));
+  if (bytes_read < 0) {
+    if (errno == EAGAIN) {
+      read_complete_ = callback;
+      pending_buffer_ = buffer;
+      pending_buffer_len_ = buffer_len;
+    } else {
+      NOTREACHED() << "read(): " << errno;
+      return false;
+    }
+  } else {
+    callback.Run(bytes_read);
+  }
+  return true;
+}
+
+bool AsyncSocketIoHandler::Initialize(base::SyncSocket::Handle socket) {
+  DCHECK_EQ(socket_, base::SyncSocket::kInvalidHandle);
+
+  DetachFromThread();
+
+  socket_ = socket;
+
+  // SyncSocket is blocking by default, so let's convert it to non-blocking.
+  int value = fcntl(socket, F_GETFL);
+  if (!(value & O_NONBLOCK)) {
+    // Set the socket to be non-blocking so we can do async reads.
+    if (fcntl(socket, F_SETFL, O_NONBLOCK) == -1) {
+      NOTREACHED();
+      return false;
+    }
+  }
+
+  return true;
+}
+
+void AsyncSocketIoHandler::EnsureWatchingSocket() {
+  DCHECK(CalledOnValidThread());
+  if (!is_watching_ && socket_ != base::SyncSocket::kInvalidHandle) {
+    is_watching_ = MessageLoopForIO::current()->WatchFileDescriptor(
+        socket_, true, MessageLoopForIO::WATCH_READ, &socket_watcher_, this);
+  }
+}
+
+}  // namespace media.