Reland of "Add thread-local allocation context for tracing"

base/trace_event/memory_profiler_allocation_context.cc

+// Copyright 2015 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/trace_event/memory_profiler_allocation_context.h"
+
+#include "base/threading/thread_local_storage.h"
+
+namespace base {
+namespace trace_event {
+
+subtle::Atomic32 AllocationContextTracker::capture_enabled_ = 0;
+
+namespace {
+ThreadLocalStorage::StaticSlot g_tls_alloc_ctx_tracker = TLS_INITIALIZER;
+}
+
+AllocationStack::AllocationStack() {}
+AllocationStack::~AllocationStack() {}
+
+// This function is added to the TLS slot to clean up the instance when the
+// thread exits.
+void DestructAllocationContextTracker(void* alloc_ctx_tracker) {
+  delete static_cast<AllocationContextTracker*>(alloc_ctx_tracker);
+}
+
+AllocationContextTracker* AllocationContextTracker::GetThreadLocalTracker() {
+  AllocationContextTracker* tracker;
+
+  if (g_tls_alloc_ctx_tracker.initialized()) {

[Dmitry Skiba, 2015/09/29 19:00:16]

Hmm, so we are setting g_tls_alloc_ctx_tracker value only once? Shouldn't this
be .Get() instead? (And .Set() in else branch, and .Initialize() as a separate
thread-safe test?)

[Primiano Tucci (use gerrit), 2015/09/30 08:26:31]

Ahh I think I see your point. Yes, looks like the TLS .Initialize() should be
called once per all, not once per thread (the dtor would still be executed per
thread).
Right, I think this CL needs to be changed as follow:

move initialized() check + Initialize to SetCaptureEnabled() (making the
capture_enabled_ fully barrierer-ed)

In this code we should just:
get() else set()


capture_enabled() should be strengthened to respect the barrier in the slow
path, i.e.

bool capture_enabled()
{
 if (!UNLIKELY(subtle::NoBarrier_Load(&capture_enabled_)))
   return false;
 
  // At this point we are in the slow path
  // Do a barriered read, as the previous one is not enough to guarantee that
the TLS has been constructed (not on all platforms).
  if (!subtle::Acquire_Load(&capture_enabled_))))
    return false;

  return true;
}

+    tracker =
+        static_cast<AllocationContextTracker*>(g_tls_alloc_ctx_tracker.Get());
+  } else {
+    tracker = new AllocationContextTracker();
+    g_tls_alloc_ctx_tracker.Initialize(DestructAllocationContextTracker);
+    g_tls_alloc_ctx_tracker.Set(tracker);
+  }
+
+  return tracker;
+}
+
+AllocationContextTracker::AllocationContextTracker() {}
+AllocationContextTracker::~AllocationContextTracker() {}
+
+// static
+void AllocationContextTracker::SetCaptureEnabled(bool enabled) {
+  // There is no memory barrier here for performance reasons, a little lag is
+  // not an issue.
+  subtle::NoBarrier_Store(&capture_enabled_, enabled);
+}
+
+// static
+void AllocationContextTracker::PushPseudoStackFrame(StackFrame frame) {
+  auto tracker = AllocationContextTracker::GetThreadLocalTracker();
+  tracker->pseudo_stack_.push(frame);
+}
+
+// static
+void AllocationContextTracker::PopPseudoStackFrame(StackFrame frame) {
+  auto tracker = AllocationContextTracker::GetThreadLocalTracker();
+  DCHECK_EQ(frame, *tracker->pseudo_stack_.top());
+  tracker->pseudo_stack_.pop();
+}
+
+// static
+void AllocationContextTracker::SetContextField(const char* key,
+                                               const char* value) {
+  auto tracker = AllocationContextTracker::GetThreadLocalTracker();
+  tracker->context_[key] = value;
+}
+
+// static
+void AllocationContextTracker::UnsetContextField(const char* key) {
+  auto tracker = AllocationContextTracker::GetThreadLocalTracker();
+  tracker->context_.erase(key);
+}
+
+// static
+AllocationStack* AllocationContextTracker::GetPseudoStackForTesting() {
+  auto tracker = AllocationContextTracker::GetThreadLocalTracker();
+  return &tracker->pseudo_stack_;
+}
+
+// static
+AllocationContext AllocationContextTracker::GetContext() {
+  // TODO(ruuda): Implement this in a follow-up CL.
+  return AllocationContext();
+}
+
+}  // namespace trace_event
+}  // namespace base