Provide an iOS message pump for IO implementation.

base/message_pump_io_ios.h

+// Copyright 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.
+
+#ifndef BASE_MESSAGE_PUMP_IO_IOS_H_
+#define BASE_MESSAGE_PUMP_IO_IOS_H_
+
+#include "base/mac/scoped_cffiledescriptorref.h"
+#include "base/mac/scoped_cftyperef.h"
+#include "base/message_pump_mac.h"
+#include "base/observer_list.h"
+
+namespace base {
+
+// This file introduces a class to monitor sockets and issue callbacks when
+// sockets are ready for I/O on iOS.
+class MessagePumpIOSForIO : public MessagePumpNSRunLoop {

[Mark Mentovai, 2012/11/20 14:47:58]

Is there a reason you used the NSRunLoop flavor and not the CFRunLoop one? Just
curious.

[blundell, 2012/11/20 20:38:54]

When we were originally bringing up this code, we experienced problems using the
CFRunLoop flavor that disappeared when we moved to the NSRunLoop flavor. We
didn't figure out what the root cause was at that time. I didn't revisit that
decision when doing this work. :|

On 2012/11/20 14:47:58, Mark Mentovai wrote:

[wtc, 2012/11/20 21:04:09]

I remember I tracked that down and discussed the problem
with Mark. We depend on something that we do in NSRunLoop
but not in CFRunLoop. I seem to remember I wrote a
proof-of-concept patch to make CFRunLoop work as well, but
didn't pursue it further.

Note: when I last worked on this, I became fascinated by the
message loop code and spent a lot of time understanding it.
I gradually realized that any issue I found could be
"working as intended" or could take a lot of effort to
explain to a code reviewer. Eventually I gave up.

+ public:
+  class IOObserver {
+   public:
+    IOObserver() {}
+
+    // An IOObserver is an object that receives IO notifications from the
+    // MessagePump.
+    //
+    // NOTE: An IOObserver implementation should be extremely fast!
+    virtual void WillProcessIOEvent() = 0;
+    virtual void DidProcessIOEvent() = 0;
+
+   protected:
+    virtual ~IOObserver() {}
+  };
+
+  // Used with WatchFileDescptor to asynchronously monitor the I/O readiness of
+  // a File Descriptor.
+  class Watcher {
+   public:
+    virtual ~Watcher() {}
+
+    // Called from MessageLoop::Run when an FD can be read from/written to
+    // without blocking
+    virtual void OnFileCanReadWithoutBlocking(int fd) = 0;
+    virtual void OnFileCanWriteWithoutBlocking(int fd) = 0;
+  };
+
+  // Object returned by WatchFileDescriptor to manage further watching.
+  class FileDescriptorWatcher {
+   public:
+    FileDescriptorWatcher();
+    ~FileDescriptorWatcher();  // Implicitly calls StopWatchingFileDescriptor.
+
+    // NOTE: These methods aren't called StartWatching()/StopWatching() to
+    // avoid confusion with the win32 ObjectWatcher class.
+
+    // Stop watching the FD, always safe to call.  No-op if there's nothing
+    // to do.
+    bool StopWatchingFileDescriptor();
+
+   private:
+    friend class MessagePumpIOSForIO;
+
+    // Called by MessagePumpIOSForIO, ownership of |fdref| and |fd_source|
+    // is transferred to this object.
+    void Init(CFFileDescriptorRef fdref,
+              CFOptionFlags callback_types,
+              CFRunLoopSourceRef fd_source,
+              bool is_persistent);
+
+    void set_pump(MessagePumpIOSForIO* pump) { pump_ = pump; }
+    MessagePumpIOSForIO* pump() const { return pump_; }
+
+    void set_watcher(Watcher* watcher) { watcher_ = watcher; }
+
+    void OnFileCanReadWithoutBlocking(int fd, MessagePumpIOSForIO* pump);
+    void OnFileCanWriteWithoutBlocking(int fd, MessagePumpIOSForIO* pump);
+
+    bool is_persistent_;  // false if this event is one-shot.
+    base::mac::ScopedCFFileDescriptorRef fdref_;
+    CFOptionFlags callback_types_;
+    base::mac::ScopedCFTypeRef<CFRunLoopSourceRef> fd_source_;
+    MessagePumpIOSForIO* pump_;
+    Watcher* watcher_;
+
+    DISALLOW_COPY_AND_ASSIGN(FileDescriptorWatcher);
+  };
+
+  enum Mode {
+    WATCH_READ = 1 << 0,
+    WATCH_WRITE = 1 << 1,
+    WATCH_READ_WRITE = WATCH_READ | WATCH_WRITE

[Mark Mentovai, 2012/11/20 14:47:58]

I don’t know that this needs to be distinct here. You can leave the read-write
enum member in message_loop.h to maintain a consistent interface and have it OR
the bits together in that header. I can’t justify having a distinct read-write
enum value here when the implementation never uses this value, it just tests the
read and write bits.

[blundell, 2012/11/20 20:38:54]

Done. I noticed that the same argument could be applied to
message_pump_libevent. Should I make that change as well?

On 2012/11/20 14:47:58, Mark Mentovai wrote:

+  };
+
+  MessagePumpIOSForIO();
+
+  // Have the current thread's message loop watch for a a situation in which
+  // reading/writing to the FD can be performed without blocking.
+  // Callers must provide a preallocated FileDescriptorWatcher object which
+  // can later be used to manage the lifetime of this event.
+  // If a FileDescriptorWatcher is passed in which is already attached to
+  // an event, then the effect is cumulative i.e. after the call |controller|
+  // will watch both the previous event and the new one.
+  // If an error occurs while calling this method in a cumulative fashion, the
+  // event previously attached to |controller| is aborted.
+  // Returns true on success.
+  // Must be called on the same thread the message_pump is running on.
+  bool WatchFileDescriptor(int fd,
+                           bool persistent,
+                           Mode mode,
+                           FileDescriptorWatcher *controller,
+                           Watcher *delegate);
+
+  void RemoveRunLoopSource(CFRunLoopSourceRef source);
+
+  void AddIOObserver(IOObserver* obs);
+  void RemoveIOObserver(IOObserver* obs);
+
+ protected:
+  virtual ~MessagePumpIOSForIO();
+
+ private:
+  void WillProcessIOEvent();
+  void DidProcessIOEvent();
+
+  static void HandleFdIOEvent(CFFileDescriptorRef fdref,
+                              CFOptionFlags callback_types,
+                              void* context);
+
+  ObserverList<IOObserver> io_observers_;
+  ThreadChecker watch_file_descriptor_caller_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(MessagePumpIOSForIO);
+};
+
+}  // namespace base
+
+#endif // BASE_MESSAGE_PUMP_IO_IOS_H_