net: Implement canceling of all async operations in FileStream.

net/base/file_stream.h

Index: net/base/file_stream.h
===================================================================
--- net/base/file_stream.h	(revision 151422)
+++ net/base/file_stream.h	(working copy)
@@ -15,11 +15,6 @@
 #include "net/base/file_stream_whence.h"
 #include "net/base/net_export.h"
 #include "net/base/net_log.h"
-#if defined(OS_WIN)
-#include "net/base/file_stream_win.h"
-#elif defined(OS_POSIX)
-#include "net/base/file_stream_posix.h"
-#endif
 
 class FilePath;
 
@@ -39,8 +34,8 @@
   // opened.
   // |net_log| is the net log pointer to use to create a |BoundNetLog|.  May be
   // NULL if logging is not needed.
-  // The already opened file will not be automatically closed when FileStream
-  // is destructed.
+  // Note: the new FileStream object takes ownership of the PlatformFile and
+  // will close it on destruction.
   FileStream(base::PlatformFile file, int flags, net::NetLog* net_log);
 
   // If the file stream was opened with Open() or OpenSync(), the underlying
@@ -62,7 +57,8 @@
   // Call this method to close the FileStream synchronously.
   // It is OK to call CloseSync() multiple times.  Redundant calls are
   // ignored. Note that if there are any pending async operations, they'll
-  // be aborted.
+  // be aborted and actual closing of the stream will happen asynchronously
+  // (to avoid races with async operation).
   virtual void CloseSync();
 
   // Call this method to open the FileStream asynchronously.  The remaining
@@ -216,12 +212,18 @@
   base::PlatformFile GetPlatformFileForTesting();
 
  private:
-#if defined(OS_WIN)
-  FileStreamWin impl_;
-#elif defined(OS_POSIX)
-  FileStreamPosix impl_;
-#endif
+  class AsyncContext;

[willchan no longer on Chromium, 2012/08/27 06:24:06]

How about we just call it Context. It's not necessarily async, as you noted
below. Also, how about we wrap it within a scoped_ptr. Then if it's in sync
mode, just delete it. If it's in async mode, use
scoped_ptr<T>::release()->Orphan(). Rename |Context::destroyed_| to
|Context::orphaned_|.

I prefer this to Destroy(), since Destroy() has different behaviors based on
sync/async. I'd rather convey that FileStream generally owns the Context, by
putting it in a scoped_ptr and explicitly Orphan()'ing it when necessary. This
is done elsewhere in the codebase too, so there's precedence for it.

 
+  bool is_async() { return !!(open_flags_ & base::PLATFORM_FILE_ASYNC); }
+
+  // Context performing I/O operations. Despite its name the context is used
+  // for synchronous operations too, but it was extracted into separate class
+  // to perform asynchronous operations correctly.
+  AsyncContext* context_;
+
+  int open_flags_;
+  net::BoundNetLog bound_net_log_;
+
   DISALLOW_COPY_AND_ASSIGN(FileStream);
 };