base: Improve DiscardableSharedMemory support for ashmem.

base/memory/discardable_shared_memory.cc

 // Copyright 2014 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 "base/memory/discardable_shared_memory.h"
 
 #if defined(OS_POSIX)
 #include <unistd.h>
 #endif
 
@@ skipping 139 matching lines @@
 
   locked_page_count_ = AlignToPageSize(mapped_size_) / base::GetPageSize();
 #if DCHECK_IS_ON()
   for (size_t page = 0; page < locked_page_count_; ++page)
     locked_pages_.insert(page);
 #endif
 
   return true;
 }
 
-bool DiscardableSharedMemory::Lock(size_t offset, size_t length) {
+DiscardableSharedMemory::LockResult DiscardableSharedMemory::Lock(
+    size_t offset, size_t length) {
   DCHECK_EQ(AlignToPageSize(offset), offset);
   DCHECK_EQ(AlignToPageSize(length), length);
 
   // Calls to this function must synchronized properly.
   DFAKE_SCOPED_LOCK(thread_collision_warner_);
 
   // Return false when instance has been purged or not initialized properly by
   // checking if |last_known_usage_| is NULL.
   if (last_known_usage_.is_null())
-    return false;
+    return FAILED;
 
   DCHECK(shared_memory_.memory());
 
   // We need to successfully acquire the platform independent lock before
   // individual pages can be locked.
   if (!locked_page_count_) {
     SharedState old_state(SharedState::UNLOCKED, last_known_usage_);
     SharedState new_state(SharedState::LOCKED, Time());
     SharedState result(subtle::Acquire_CompareAndSwap(
         &SharedStateFromSharedMemory(shared_memory_)->value.i,
         old_state.value.i,
         new_state.value.i));
     if (result.value.u != old_state.value.u) {
       // Update |last_known_usage_| in case the above CAS failed because of
       // an incorrect timestamp.
       last_known_usage_ = result.GetTimestamp();
-      return false;
+      return FAILED;
     }
   }
 
   // Zero for length means "everything onward".
   if (!length)
     length = AlignToPageSize(mapped_size_) - offset;
 
   size_t start = offset / base::GetPageSize();
   size_t end = start + length / base::GetPageSize();
   DCHECK_LT(start, end);
   DCHECK_LE(end, AlignToPageSize(mapped_size_) / base::GetPageSize());
 
   // Add pages to |locked_page_count_|.
   // Note: Locking a page that is already locked is an error.
   locked_page_count_ += end - start;
 #if DCHECK_IS_ON()
   // Detect incorrect usage by keeping track of exactly what pages are locked.
   for (auto page = start; page < end; ++page) {
     auto result = locked_pages_.insert(page);
     DCHECK(result.second);
   }
   DCHECK_EQ(locked_pages_.size(), locked_page_count_);
 #endif
 
 #if defined(OS_ANDROID)
   SharedMemoryHandle handle = shared_memory_.handle();
   DCHECK(SharedMemory::IsHandleValid(handle));
   if (ashmem_pin_region(
           handle.fd, AlignToPageSize(sizeof(SharedState)) + offset, length)) {
-    return false;
+    return PURGED;
   }
 #endif
 
-  return true;
+  return SUCCESS;
 }
 
 void DiscardableSharedMemory::Unlock(size_t offset, size_t length) {
   DCHECK_EQ(AlignToPageSize(offset), offset);
   DCHECK_EQ(AlignToPageSize(length), length);
 
   // Calls to this function must synchronized properly.
   DFAKE_SCOPED_LOCK(thread_collision_warner_);
 
   // Zero for length means "everything onward".
@@ skipping 122 matching lines @@
   shared_memory_.Unmap();
   shared_memory_.Close();
   mapped_size_ = 0;
 }
 
 Time DiscardableSharedMemory::Now() const {
   return Time::Now();
 }
 
 }  // namespace base