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 115 matching lines @@
 void InvokeCallbackIfBackendIsAlive(
     const base::WeakPtr<SimpleBackendImpl>& backend,
     const net::CompletionCallback& completion_callback,
     int result) {
   DCHECK(!completion_callback.is_null());
   if (!backend.get())
     return;
   completion_callback.Run(result);
 }
 
+// If |sync_possible| is false, and callback is available, posts rv to it and
+// return net::ERR_IO_PENDING; otherwise just passes through rv.
+int PostToCallbackIfNeeded(bool sync_possible,
+                           const net::CompletionCallback& callback,
+                           int rv) {
+  if (!sync_possible && !callback.is_null()) {
+    base::ThreadTaskRunnerHandle::Get()->PostTask(FROM_HERE,
+                                                  base::Bind(callback, rv));
+    return net::ERR_IO_PENDING;
+  } else {
+    return rv;
+  }
+}
+
 }  // namespace
 
 using base::Closure;
 using base::FilePath;
 using base::Time;
 using base::TaskRunner;
 
 // Static function called by base::trace_event::EstimateMemoryUsage() to
 // estimate the memory of SimpleEntryOperation.
 // This needs to be in disk_cache namespace.
@@ skipping 217 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;
-  }
-
-  // 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;
+
+  if (alone_in_queue) {
+    return ReadDataInternal(/*sync_possible = */ true, stream_index, offset,
+                            buf, buf_len, callback);
+  }
+
   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 227 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(),
-                         operation->callback());
+        ReadDataInternal(/* sync_possible= */ 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());
         break;
@@ skipping 150 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 sync_possible,
+                                      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()) {
-      RecordReadResult(cache_type_, READ_RESULT_BAD_STATE);
-      // 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));
-    }
+    RecordReadResult(cache_type_, READ_RESULT_BAD_STATE);
     if (net_log_.IsCapturing()) {
       net_log_.AddEvent(net::NetLogEventType::SIMPLE_CACHE_ENTRY_READ_END,
                         CreateNetLogReadWriteCompleteCallback(net::ERR_FAILED));
     }
-    return;
+    // 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.
+    return PostToCallbackIfNeeded(sync_possible, callback, 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_, sync_possible
+                                      ? 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())
-      base::ThreadTaskRunnerHandle::Get()->PostTask(FROM_HERE,
-                                                    base::Bind(callback, 0));
-    return;
+    // STATE_IO_PENDING (so ScopedOperationRunner might start us on next op
+    // here).
+    return PostToCallbackIfNeeded(sync_possible, callback, 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) {
-    ReadFromBufferAndPostReply(stream_0_data_.get(), offset, buf_len, buf,
-                               callback);
-    return;
+    int rv = ReadFromBuffer(stream_0_data_.get(), offset, buf_len, buf);
+    return PostToCallbackIfNeeded(sync_possible, callback, rv);
   }
 
   // Sometimes we can read in-ram prefetched stream 1 data immediately, too.
   if (stream_index == 1) {
     if (is_initial_stream1_read_) {
       SIMPLE_CACHE_UMA(BOOLEAN, "ReadStream1FromPrefetched", cache_type_,
                        stream_1_prefetch_data_ != nullptr);
     }
     is_initial_stream1_read_ = false;
 
     if (stream_1_prefetch_data_) {
-      ReadFromBufferAndPostReply(stream_1_prefetch_data_.get(), offset, buf_len,
-                                 buf, callback);
-      return;
+      int rv =
+          ReadFromBuffer(stream_1_prefetch_data_.get(), offset, buf_len, buf);
+      return PostToCallbackIfNeeded(sync_possible, callback, rv);
     }
   }
 
   state_ = STATE_IO_PENDING;
   if (!doomed_ && backend_.get())
     backend_->index()->UseIfExists(entry_hash_);
 
   // Figure out if we should be computing the checksum for this read,
   // and whether we should be verifying it, too.
   std::unique_ptr<SimpleSynchronousEntry::CRCRequest> crc_request;
@@ skipping 15 matching lines @@
   Closure task = base::Bind(
       &SimpleSynchronousEntry::ReadData, base::Unretained(synchronous_entry_),
       SimpleSynchronousEntry::EntryOperationData(stream_index, offset, buf_len),
       crc_request.get(), entry_stat.get(), base::RetainedRef(buf),
       result.get());
   Closure reply =
       base::Bind(&SimpleEntryImpl::ReadOperationComplete, this, stream_index,
                  offset, callback, base::Passed(&crc_request),
                  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 553 matching lines @@
     } else {
       type = conflicting ? WRITE_FOLLOWS_CONFLICTING_WRITE
                          : WRITE_FOLLOWS_NON_CONFLICTING_WRITE;
     }
   }
   SIMPLE_CACHE_UMA(ENUMERATION,
                    "WriteDependencyType", cache_type_,
                    type, WRITE_DEPENDENCY_TYPE_MAX);
 }
 
-void SimpleEntryImpl::ReadFromBufferAndPostReply(
-    net::GrowableIOBuffer* in_buf,
-    int offset,
-    int buf_len,
-    net::IOBuffer* out_buf,
-    const CompletionCallback& callback) {
-  int rv;
-  if (buf_len < 0) {
-    RecordReadResult(cache_type_, READ_RESULT_SYNC_READ_FAILURE);
-    rv = 0;
-  } else {
-    memcpy(out_buf->data(), in_buf->data() + offset, buf_len);
-    UpdateDataFromEntryStat(SimpleEntryStat(base::Time::Now(), last_modified_,
-                                            data_size_, sparse_data_size_));
-    RecordReadResult(cache_type_, READ_RESULT_SUCCESS);
-    rv = buf_len;
-  }
-  if (!callback.is_null()) {
-    base::ThreadTaskRunnerHandle::Get()->PostTask(FROM_HERE,
-                                                  base::Bind(callback, rv));
-  }
+int SimpleEntryImpl::ReadFromBuffer(net::GrowableIOBuffer* in_buf,
+                                    int offset,
+                                    int buf_len,
+                                    net::IOBuffer* out_buf) {
+  DCHECK_GE(buf_len, 0);
+
+  memcpy(out_buf->data(), in_buf->data() + offset, buf_len);
+  UpdateDataFromEntryStat(SimpleEntryStat(base::Time::Now(), last_modified_,
+                                          data_size_, sparse_data_size_));
+  RecordReadResult(cache_type_, READ_RESULT_SUCCESS);
+  return buf_len;
 }
 
 int SimpleEntryImpl::SetStream0Data(net::IOBuffer* buf,
                                     int offset,
                                     int buf_len,
                                     bool truncate) {
   // Currently, stream 0 is only used for HTTP headers, and always writes them
   // with a single, truncating write. Detect these writes and record the size
   // changes of the headers. Also, support writes to stream 0 that have
   // different access patterns, as required by the API contract.
@@ skipping 46 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