Make SimpleEntryImpl ref counted.

net/disk_cache/simple/simple_synchronous_entry.cc

 // Copyright (c) 2013 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 "net/disk_cache/simple/simple_synchronous_entry.h"
 
 #include <algorithm>
 #include <cstring>
 #include <limits>
 
@@ skipping 67 matching lines @@
     delete sync_entry;
     sync_entry = NULL;
   }
   callback_runner->PostTask(FROM_HERE, base::Bind(callback, sync_entry));
 }
 
 // static
 void SimpleSynchronousEntry::DoomEntry(
     const FilePath& path,
     const std::string& key,
-    scoped_refptr<TaskRunner> callback_runner,
+    const scoped_refptr<TaskRunner>& callback_runner,
     const net::CompletionCallback& callback) {
   for (int i = 0; i < kSimpleEntryFileCount; ++i) {
     FilePath to_delete = path.AppendASCII(GetFilenameFromKeyAndIndex(key, i));
     bool ALLOW_UNUSED result = file_util::Delete(to_delete, false);
     DLOG_IF(ERROR, !result) << "Could not delete " << to_delete.MaybeAsASCII();
   }
   if (!callback.is_null())
     callback_runner->PostTask(FROM_HERE, base::Bind(callback, net::OK));
 }
 
@@ skipping 14 matching lines @@
   DCHECK(initialized_);
 
   int64 file_offset = GetFileOffsetFromKeyAndDataOffset(key_, offset);
   int bytes_read = ReadPlatformFile(files_[index], file_offset,
                                     buf->data(), buf_len);
   if (bytes_read > 0)
     last_used_ = Time::Now();
   int result = (bytes_read >= 0) ? bytes_read : net::ERR_FAILED;
   if (result == net::ERR_FAILED)
     Doom();
   callback_runner_->PostTask(FROM_HERE, base::Bind(callback, result));

[gavinp, 2013/04/20 07:28:33]

***ONE*** A context switch occurs precisely after running this statement,
leaving the program counter inside of SimpleSynchronousEntry::ReadData(). Note
it's called from a Closure(), and that closure has a ref to |callback|, which
has a |scoped_refptr<SimpleEntryImpl>| as part of it.

 }

[gavinp, 2013/04/20 07:28:33]

***FIVE*** Control flow continues at this point. The SimpleEntryImpl object is
deleted on the worker pool.

 
 void SimpleSynchronousEntry::WriteData(
     int index,
     int offset,
     net::IOBuffer* buf,
     int buf_len,
     const SynchronousOperationCallback& callback,
     bool truncate) {
   DCHECK(initialized_);
 
@@ skipping 164 matching lines @@
   return net::OK;
 }
 
 void SimpleSynchronousEntry::Doom() {
   // TODO(gavinp): Consider if we should guard against redundant Doom() calls.
   DoomEntry(path_, key_,
             scoped_refptr<base::TaskRunner>(), net::CompletionCallback());
 }
 
 }  // namespace disk_cache