Re-land: base: Fix registering of memory pressure listeners used when emulating discardable memory.

base/memory/discardable_memory_provider.cc

Index: base/memory/discardable_memory_provider.cc
diff --git a/base/memory/discardable_memory_provider.cc b/base/memory/discardable_memory_provider.cc
index 1c84339eba7aea5877446f893a94a019c2605def..eeffa5b25ad1c7392791f0f639feeeea53f7b365 100644
--- a/base/memory/discardable_memory_provider.cc
+++ b/base/memory/discardable_memory_provider.cc
@@ -29,10 +29,7 @@ DiscardableMemoryProvider::DiscardableMemoryProvider()
       bytes_allocated_(0),
       discardable_memory_limit_(kDefaultDiscardableMemoryLimit),
       bytes_to_reclaim_under_moderate_pressure_(
-          kDefaultBytesToReclaimUnderModeratePressure),
-      memory_pressure_listener_(
-          base::Bind(&DiscardableMemoryProvider::NotifyMemoryPressure,
-                     Unretained(this))) {
+          kDefaultBytesToReclaimUnderModeratePressure) {
 }
 
 DiscardableMemoryProvider::~DiscardableMemoryProvider() {
@@ -40,18 +37,20 @@ DiscardableMemoryProvider::~DiscardableMemoryProvider() {
   DCHECK_EQ(0u, bytes_allocated_);
 }
 
-void DiscardableMemoryProvider::NotifyMemoryPressure(
-    MemoryPressureListener::MemoryPressureLevel pressure_level) {
-  switch (pressure_level) {
-    case MemoryPressureListener::MEMORY_PRESSURE_MODERATE:
-      Purge();
-      return;
-    case MemoryPressureListener::MEMORY_PRESSURE_CRITICAL:
-      PurgeAll();
-      return;
-  }
+void DiscardableMemoryProvider::RegisterMemoryPressureListener() {
+  AutoLock lock(lock_);
+  DCHECK(base::MessageLoop::current());
+  DCHECK(!memory_pressure_listener_);
+  memory_pressure_listener_.reset(
+      new MemoryPressureListener(
+          base::Bind(&DiscardableMemoryProvider::OnMemoryPressure,
+                     Unretained(this))));
+}
 
-  NOTREACHED();
+void DiscardableMemoryProvider::UnregisterMemoryPressureListener() {
+  AutoLock lock(lock_);
+  DCHECK(memory_pressure_listener_);
+  memory_pressure_listener_.reset();
 }
 
 void DiscardableMemoryProvider::SetDiscardableMemoryLimit(size_t bytes) {
@@ -69,6 +68,11 @@ void DiscardableMemoryProvider::SetBytesToReclaimUnderModeratePressure(
 void DiscardableMemoryProvider::Register(
     const DiscardableMemory* discardable, size_t bytes) {
   AutoLock lock(lock_);
+  // A registered memory listener is currently required. This DCHECK can be
+  // moved or removed if we decide that it's useful to relax this condition.
+  // TODO(reveman): Enable this DCHECK when skia and blink are able to
+  // register memory pressure listeners. crbug.com/333907
+  // DCHECK(memory_pressure_listener_);

[reveman, 2014/01/13 18:22:28]

Disabled this DCHECK for now as it's causing webkit_unit_tests to fail. I will
re-enable this as soon as I've added the necessary APIs to blink and skia that
allow us to enforce this everywhere.

   DCHECK(allocations_.Peek(discardable) == allocations_.end());
   allocations_.Put(discardable, Allocation(bytes));
 }
@@ -169,6 +173,20 @@ size_t DiscardableMemoryProvider::GetBytesAllocatedForTest() const {
   return bytes_allocated_;
 }
 
+void DiscardableMemoryProvider::OnMemoryPressure(
+    MemoryPressureListener::MemoryPressureLevel pressure_level) {
+  switch (pressure_level) {
+    case MemoryPressureListener::MEMORY_PRESSURE_MODERATE:
+      Purge();
+      return;
+    case MemoryPressureListener::MEMORY_PRESSURE_CRITICAL:
+      PurgeAll();
+      return;
+  }
+
+  NOTREACHED();
+}
+
 void DiscardableMemoryProvider::Purge() {
   AutoLock lock(lock_);