SimpleCache: synchronously reply on reads from idle if data is in memory.

net/disk_cache/simple/simple_entry_impl.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_entry_impl.h"
 
 #include <algorithm>
 #include <cstring>
 #include <limits>
 #include <utility>
@@ skipping 358 matching lines @@
       buf_len < 0) {
     if (net_log_.IsCapturing()) {
       net_log_.AddEvent(
           net::NetLogEventType::SIMPLE_CACHE_ENTRY_READ_END,
           CreateNetLogReadWriteCompleteCallback(net::ERR_INVALID_ARGUMENT));
     }
 
     RecordReadResult(cache_type_, READ_RESULT_INVALID_ARGUMENT);
     return net::ERR_INVALID_ARGUMENT;
   }
-  if (pending_operations_.empty() && (offset >= GetDataSize(stream_index) ||
-                                      offset < 0 || !buf_len)) {
-    if (net_log_.IsCapturing()) {
-      net_log_.AddEvent(net::NetLogEventType::SIMPLE_CACHE_ENTRY_READ_END,
-                        CreateNetLogReadWriteCompleteCallback(0));
-    }
 
-    RecordReadResult(cache_type_, READ_RESULT_NONBLOCK_EMPTY_RETURN);
-    return 0;
+  bool alone_in_queue =
+      pending_operations_.size() == 0 && state_ == STATE_READY;
+
+  if (alone_in_queue) {
+    return ReadDataInternal(true, stream_index, offset, buf, buf_len, callback);
   }
 
-  // TODO(clamy): return immediatly when reading from stream 0.
-
-  // TODO(felipeg): Optimization: Add support for truly parallel read
-  // operations.
-  bool alone_in_queue =
-      pending_operations_.size() == 0 && state_ == STATE_READY;
   pending_operations_.push(SimpleEntryOperation::ReadOperation(
       this, stream_index, offset, buf_len, buf, callback, alone_in_queue));
   RunNextOperationIfNeeded();
   return net::ERR_IO_PENDING;
 }
 
 int SimpleEntryImpl::WriteData(int stream_index,
                                int offset,
                                net::IOBuffer* buf,
                                int buf_len,
@@ skipping 226 matching lines @@
       case SimpleEntryOperation::TYPE_CREATE:
         CreateEntryInternal(operation->have_index(),
                             operation->callback(),
                             operation->out_entry());
         break;
       case SimpleEntryOperation::TYPE_CLOSE:
         CloseInternal();
         break;
       case SimpleEntryOperation::TYPE_READ:
         RecordReadIsParallelizable(*operation);
-        ReadDataInternal(operation->index(),
-                         operation->offset(),
-                         operation->buf(),
-                         operation->length(),
+        ReadDataInternal(false, operation->index(), operation->offset(),
+                         operation->buf(), operation->length(),
                          operation->callback());
         break;
       case SimpleEntryOperation::TYPE_WRITE:
         RecordWriteDependencyType(*operation);
         WriteDataInternal(operation->index(),
                           operation->offset(),
                           operation->buf(),
                           operation->length(),
                           operation->callback(),
                           operation->truncate());
@@ skipping 155 matching lines @@
         SIMPLE_CACHE_UMA(ENUMERATION,
                          "CheckCRCResult", cache_type_,
                          crc_check_state_[i], CRC_CHECK_MAX);
       }
     }
   } else {
     CloseOperationComplete();
   }
 }
 
-void SimpleEntryImpl::ReadDataInternal(int stream_index,
-                                       int offset,
-                                       net::IOBuffer* buf,
-                                       int buf_len,
-                                       const CompletionCallback& callback) {
+int SimpleEntryImpl::ReadDataInternal(bool try_sync,
+                                      int stream_index,
+                                      int offset,
+                                      net::IOBuffer* buf,
+                                      int buf_len,
+                                      const CompletionCallback& callback) {
   DCHECK(io_thread_checker_.CalledOnValidThread());
   ScopedOperationRunner operation_runner(this);
 
   if (net_log_.IsCapturing()) {
     net_log_.AddEvent(net::NetLogEventType::SIMPLE_CACHE_ENTRY_READ_BEGIN,
                       CreateNetLogReadWriteDataCallback(stream_index, offset,
                                                         buf_len, false));
   }
 
   if (state_ == STATE_FAILURE || state_ == STATE_UNINITIALIZED) {
-    if (!callback.is_null()) {
+    if (!callback.is_null() && !try_sync) {
       RecordReadResult(cache_type_, READ_RESULT_BAD_STATE);

[Maks Orlovich, 2017/04/12 14:55:49]

I should probably double-check the condition for this one...

[pasko, 2017/04/12 16:12:51]

this won't appear on the benchmark, so why bother?

       // Note that the API states that client-provided callbacks for entry-level
       // (i.e. non-backend) operations (e.g. read, write) are invoked even if
       // the backend was already destroyed.
       base::ThreadTaskRunnerHandle::Get()->PostTask(
           FROM_HERE, base::Bind(callback, net::ERR_FAILED));
     }
     if (net_log_.IsCapturing()) {
       net_log_.AddEvent(net::NetLogEventType::SIMPLE_CACHE_ENTRY_READ_END,
                         CreateNetLogReadWriteCompleteCallback(net::ERR_FAILED));
     }
-    return;
+    return net::ERR_FAILED;
   }
   DCHECK_EQ(STATE_READY, state_);
   if (offset >= GetDataSize(stream_index) || offset < 0 || !buf_len) {
-    RecordReadResult(cache_type_, READ_RESULT_FAST_EMPTY_RETURN);
+    RecordReadResult(cache_type_, try_sync ? READ_RESULT_NONBLOCK_EMPTY_RETURN
+                                           : READ_RESULT_FAST_EMPTY_RETURN);
     // If there is nothing to read, we bail out before setting state_ to
     // STATE_IO_PENDING.
-    if (!callback.is_null())
+    if (!callback.is_null() && !try_sync)
       base::ThreadTaskRunnerHandle::Get()->PostTask(FROM_HERE,
                                                     base::Bind(callback, 0));
-    return;
+    return 0;
   }
 
   buf_len = std::min(buf_len, GetDataSize(stream_index) - offset);
 
   // Since stream 0 data is kept in memory, it is read immediately.
   if (stream_index == 0) {
     int ret_value = ReadStream0Data(buf, offset, buf_len);
-    if (!callback.is_null()) {
+    if (!callback.is_null() && !try_sync) {
       base::ThreadTaskRunnerHandle::Get()->PostTask(
           FROM_HERE, base::Bind(callback, ret_value));
     }
-    return;
+    return ret_value;
   }
 
   state_ = STATE_IO_PENDING;
   if (!doomed_ && backend_.get())
     backend_->index()->UseIfExists(entry_hash_);
 
   std::unique_ptr<uint32_t> read_crc32(new uint32_t());
   std::unique_ptr<int> result(new int());
   std::unique_ptr<SimpleEntryStat> entry_stat(new SimpleEntryStat(
       last_used_, last_modified_, data_size_, sparse_data_size_));
   Closure task = base::Bind(
       &SimpleSynchronousEntry::ReadData, base::Unretained(synchronous_entry_),
       SimpleSynchronousEntry::EntryOperationData(stream_index, offset, buf_len),
       base::RetainedRef(buf), read_crc32.get(), entry_stat.get(), result.get());
   Closure reply = base::Bind(&SimpleEntryImpl::ReadOperationComplete,
                              this,
                              stream_index,
                              offset,
                              callback,
                              base::Passed(&read_crc32),
                              base::Passed(&entry_stat),
                              base::Passed(&result));
   worker_pool_->PostTaskAndReply(FROM_HERE, task, reply);
+  return net::ERR_IO_PENDING;
 }
 
 void SimpleEntryImpl::WriteDataInternal(int stream_index,
                                        int offset,
                                        net::IOBuffer* buf,
                                        int buf_len,
                                        const CompletionCallback& callback,
                                        bool truncate) {
   DCHECK(io_thread_checker_.CalledOnValidThread());
   ScopedOperationRunner operation_runner(this);
@@ skipping 658 matching lines @@
     }
     crc32s_end_offset_[stream_index] = offset + length;
   } else if (offset < crc32s_end_offset_[stream_index]) {
     // If a range for which the crc32 was already computed is rewritten, the
     // computation of the crc32 need to start from 0 again.
     crc32s_end_offset_[stream_index] = 0;
   }
 }
 
 }  // namespace disk_cache