Race Create vs SendRequest on cache misses.

net/disk_cache/pending_create_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/pending_create_entry.h"
+
+#include "base/time.h"
+#include "net/base/net_errors.h"
+#include "net/disk_cache/disk_cache.h"
+
+namespace disk_cache {
+
+namespace {
+
+// A PendingEntry takes the place of our yet to be created Entry when we perform
+// a PendingCreateEntry. After a successful create, the new Entry will switch
+// and takes it place. The PendingEntry will set the output parameter |failed|
+// to true if it receives any operation we cannot proxy on the new entry.
+class PendingEntry : public Entry {
+ public:
+  PendingEntry(const std::string& key, bool* failed) : key_(key),
+                                                       failed_(failed) {
+    *failed_ = false;
+  }
+  virtual ~PendingEntry() {
+  }
+
+  // From disk_cache::Entry:
+  virtual void Close() OVERRIDE {
+    // We do not self delete here, because as a member of ProxyEntry we will be
+    // delete with it.
+  }
+  virtual void Doom() OVERRIDE {
+  }
+  virtual int WriteData(int index,
+                        int offset,
+                        IOBuffer* buf,
+                        int buf_len,
+                        const CompletionCallback& callback,
+                        bool truncate) OVERRIDE {
+    VLOG(0) << "NETWORK won for " << key_;
+    // If we receive WriteData, that's because the create on the disk cache did
+    // not complete in time to receive data. We fail, which will force
+    // transactions into pass through mode.
+    // TODO(gavinp): Investigate the benefit of buffering here.
+    *failed_ = true;
+    return net::ERR_CACHE_CREATE_RACE_FAILED;
+  }
+  virtual std::string GetKey() const OVERRIDE {
+    return key_;
+  }
+
+  // The rest of these operations aren't expected to ever be called, but are
+  // required for a complete implementation of the abstract base class.
+  virtual base::Time GetLastUsed() const OVERRIDE {
+    NOTREACHED();
+    return base::Time();
+  }
+  virtual base::Time GetLastModified() const OVERRIDE {
+    NOTREACHED();
+    return base::Time();
+  }
+  virtual int32 GetDataSize(int index) const OVERRIDE {
+    NOTREACHED();
+    return 0;
+  }
+  virtual int ReadData(int index,
+                       int offset,
+                       IOBuffer* buf,
+                       int buf_len,
+                       const CompletionCallback& callback) OVERRIDE {
+    NOTREACHED();
+    return net::ERR_CACHE_CREATE_RACE_FAILED;
+  }
+  virtual int ReadSparseData(int64 offset,
+                             IOBuffer* buf,
+                             int buf_len,
+                             const CompletionCallback& callback) OVERRIDE {
+    NOTREACHED();
+    return net::ERR_CACHE_CREATE_RACE_FAILED;
+  }
+  virtual int WriteSparseData(int64 offset,
+                              IOBuffer* buf,
+                              int buf_len,
+                              const CompletionCallback& callback) OVERRIDE {
+    NOTREACHED();
+    return net::ERR_CACHE_CREATE_RACE_FAILED;
+  }
+  virtual int GetAvailableRange(int64 offset,
+                                int len,
+                                int64* start,
+                                const CompletionCallback& callback) OVERRIDE {
+    NOTREACHED();
+    return net::ERR_CACHE_CREATE_RACE_FAILED;
+  }
+  virtual bool CouldBeSparse() const OVERRIDE {
+    NOTREACHED();
+    return false;
+  }
+  virtual void CancelSparseIO() OVERRIDE {
+    NOTREACHED();
+  }
+  virtual int ReadyForSparseIO(const CompletionCallback& callback) OVERRIDE {
+    return net::ERR_CACHE_CREATE_RACE_FAILED;
+  }
+
+ private:
+  std::string key_;
+
+  // |failed_| is set to true iff we receive an operation we cannot proxy.
+  bool* failed_;
+};
+
+// The ProxyEntry initially proxies for a PendingEntry, and once our CreateEntry
+// is complete, it swaps it in place if possible.
+class ProxyEntry : public Entry {
+ public:
+  explicit ProxyEntry(const std::string& key);
+  virtual ~ProxyEntry();
+
+  Entry* ReleaseCreatedEntry();
+
+  Entry** to_create_entry_ptr() { return &to_create_entry_; }
+  const net::CompletionCallback& io_callback() const { return io_callback_; }
+
+  // Entry interface.
+  virtual void Doom() OVERRIDE {
+    proxy_entry_->Doom();
+  }
+  virtual void Close() OVERRIDE {
+    proxy_entry_->Close();
+    proxy_entry_ = NULL;
+    // Normally, for entries that are created uniquely per user we would self
+    // delete here. However, |to_create_entry_| is still referenced if we have
+    // not received our io_callback_ yet, so we must wait for the callback to
+    // self delete. Note that this isn't solved by using a WeakPtr in the
+    // callback, since |to_create_entry_| is set on the Cache thread outside
+    // of the callback.
+    if (io_callback_was_received_)
+      delete this;
+  }
+  virtual std::string GetKey() const OVERRIDE {
+    return proxy_entry_->GetKey();
+  }
+  virtual base::Time GetLastUsed() const OVERRIDE {
+    return proxy_entry_->GetLastUsed();
+  }
+  virtual base::Time GetLastModified() const OVERRIDE {
+    return proxy_entry_->GetLastModified();
+  }
+  virtual int32 GetDataSize(int index) const OVERRIDE {
+    return proxy_entry_->GetDataSize(index);
+  }
+  virtual int ReadData(int index, int offset, IOBuffer* buf, int buf_len,
+                       const CompletionCallback& callback) OVERRIDE {
+    return proxy_entry_->ReadData(index, offset, buf, buf_len, callback);
+  }
+  virtual int WriteData(int index, int offset, IOBuffer* buf, int buf_len,
+                        const CompletionCallback& callback,
+                        bool truncate) OVERRIDE {
+    return proxy_entry_->WriteData(index, offset, buf, buf_len, callback,
+                                   truncate);
+  }
+  virtual int ReadSparseData(int64 offset, IOBuffer* buf, int buf_len,
+                             const CompletionCallback& callback) OVERRIDE {
+    return proxy_entry_->ReadSparseData(offset, buf, buf_len, callback);
+  }
+  virtual int WriteSparseData(int64 offset, IOBuffer* buf, int buf_len,
+                              const CompletionCallback& callback) OVERRIDE {
+    return proxy_entry_->WriteSparseData(offset, buf, buf_len, callback);
+  }
+  virtual int GetAvailableRange(int64 offset, int len, int64* start,
+                                const CompletionCallback& callback) OVERRIDE {
+    return proxy_entry_->GetAvailableRange(offset, len, start, callback);
+  }
+  virtual bool CouldBeSparse() const OVERRIDE {
+    return proxy_entry_->CouldBeSparse();
+  }
+  virtual void CancelSparseIO() OVERRIDE {
+    proxy_entry_->CancelSparseIO();
+  }
+  virtual int ReadyForSparseIO(const CompletionCallback& callback) OVERRIDE {
+    return proxy_entry_->ReadyForSparseIO(callback);
+  }
+
+ private:
+  void OnIOComplete(int result);
+
+  std::string key_;
+
+  // Initially false, |pending_entry_invalid_| is set to true if the
+  // |pending_entry_| received an operation it could not proxy.
+  bool pending_entry_invalid_;
+
+  // Before we have created our entry, we use proxy to the pending issue.
+  PendingEntry pending_entry_;
+
+  bool io_callback_was_received_;
+
+  // When our IO callback is called, |to_create_entry_| will contain our newly
+  // created entry.
+  Entry* to_create_entry_;
+
+  // The entry that we are currently a proxy for.
+  Entry* proxy_entry_;
+
+  net::CompletionCallback io_callback_;
+};
+
+ProxyEntry::ProxyEntry(const std::string& key)
+      : key_(key),
+        pending_entry_invalid_(false),
+        pending_entry_(key, &pending_entry_invalid_),
+        io_callback_was_received_(false),
+        to_create_entry_(NULL),
+        proxy_entry_(&pending_entry_),
+        ALLOW_THIS_IN_INITIALIZER_LIST(io_callback_(
+            base::Bind(&ProxyEntry::OnIOComplete, base::Unretained(this)))) {
+}
+
+ProxyEntry::~ProxyEntry() {
+}
+
+Entry* ProxyEntry::ReleaseCreatedEntry() {
+  Entry* to_return = to_create_entry_;
+  to_create_entry_ = NULL;
+  return to_return;
+}
+
+void ProxyEntry::OnIOComplete(int result) {
+  DCHECK(!io_callback_was_received_);
+  io_callback_was_received_ = true;
+  if (!proxy_entry_) {
+    // We are receiving an IO callback after we have already been closed.
+    // Since |to_create_entry_| is no longer referenced by our pending Create
+    // operation, we can now perform the self delete delayed from Close().
+    VLOG(0) << "Cleaning up after our entry...";
+    to_create_entry_->Doom();
+    to_create_entry_->Close();
+    to_create_entry_ = NULL;
+    delete this;
+    return;
+  }
+  VLOG(0) << "CACHE WON for " << key_;
+  if (result == net::OK) {
+    if (pending_entry_invalid_) {
+      to_create_entry_->Doom();
+      to_create_entry_->Close();
+      to_create_entry_ = NULL;
+      return;
+    }
+    // We have successfully created our entry before any invalid operations
+    // occured. We can swap it in and become a pure proxy.
+    proxy_entry_ = to_create_entry_;
+    to_create_entry_ = NULL;
+  }
+}
+
+}  // namespace
+
+int PendingCreateEntry(Backend* backend,
+                       const std::string& key,
+                       Entry** entry) {
+  VLOG(0) << "PendingCreateEntry";
+  ProxyEntry* proxy_entry = new ProxyEntry(key);
+  int rv = backend->CreateEntry(key, proxy_entry->to_create_entry_ptr(),
+                                proxy_entry->io_callback());
+  VLOG(0) << "rv = " << rv;
+  if (rv == net::ERR_IO_PENDING) {
+    *entry = proxy_entry;
+    return net::OK;
+  }
+  if (rv == net::OK)
+    *entry = proxy_entry->ReleaseCreatedEntry();
+  return rv;
+}
+
+}  // namespace disk_cache