base: Improve DiscardableSharedMemory support for ashmem.

content/child/child_discardable_shared_memory_manager.cc

Index: content/child/child_discardable_shared_memory_manager.cc
diff --git a/content/child/child_discardable_shared_memory_manager.cc b/content/child/child_discardable_shared_memory_manager.cc
index d5b97a06153fec7c0a0dcbacfc7cfba4b20d36a6..85a746061eb29087c7d661b92139e3a8a430959a 100644
--- a/content/child/child_discardable_shared_memory_manager.cc
+++ b/content/child/child_discardable_shared_memory_manager.cc
@@ -72,10 +72,11 @@ ChildDiscardableSharedMemoryManager::AllocateLockedDiscardableMemory(
 
     // Attempt to lock |free_span|. Delete span and search free list again
     // if locking failed.
-    if (!free_span->shared_memory()->Lock(
+    if (free_span->shared_memory()->Lock(
             free_span->start() * base::GetPageSize() -
                 reinterpret_cast<size_t>(free_span->shared_memory()->memory()),
-            free_span->length() * base::GetPageSize())) {
+            free_span->length() * base::GetPageSize()) !=
+        base::DiscardableSharedMemory::SUCCESS) {
       heap_.DeleteSpan(free_span.Pass());
       continue;
     }
@@ -114,19 +115,29 @@ ChildDiscardableSharedMemoryManager::AllocateLockedDiscardableMemory(
 bool ChildDiscardableSharedMemoryManager::LockSpan(
     DiscardableSharedMemoryHeap::Span* span) {
   base::AutoLock lock(lock_);
-  return span->shared_memory()->Lock(
-      span->start() * base::GetPageSize() -
-          reinterpret_cast<size_t>(span->shared_memory()->memory()),
-      span->length() * base::GetPageSize());
+
+  size_t offset = span->start() * base::GetPageSize() -
+      reinterpret_cast<size_t>(span->shared_memory()->memory());
+  size_t length = span->length() * base::GetPageSize();
+
+  auto result = span->shared_memory()->Lock(offset, length);
+  if (result == base::DiscardableSharedMemory::SUCCESS)

[danakj, 2015/01/24 00:16:06]

switch instead of series of ifs?

[reveman, 2015/01/24 00:27:48]

Good idea. Done.

+    return true;
+  if (result == base::DiscardableSharedMemory::PURGED)
+    span->shared_memory()->Unlock(offset, length);
+
+  return false;
 }
 
 void ChildDiscardableSharedMemoryManager::UnlockSpan(
     DiscardableSharedMemoryHeap::Span* span) {
   base::AutoLock lock(lock_);
-  return span->shared_memory()->Unlock(
-      span->start() * base::GetPageSize() -
-          reinterpret_cast<size_t>(span->shared_memory()->memory()),
-      span->length() * base::GetPageSize());
+
+  size_t offset = span->start() * base::GetPageSize() -
+      reinterpret_cast<size_t>(span->shared_memory()->memory());
+  size_t length = span->length() * base::GetPageSize();
+
+  return span->shared_memory()->Unlock(offset, length);
 }
 
 bool ChildDiscardableSharedMemoryManager::IsSpanResident(