tracing: split out the CategoryRegistry from the TraceLog

base/trace_event/category_registry.cc

+// Copyright 2016 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/category_registry.h"
+
+#include <string.h>
+
+#include <type_traits>
+
+#include "base/atomicops.h"
+#include "base/debug/leak_annotations.h"
+#include "base/lazy_instance.h"
+#include "base/logging.h"
+#include "base/synchronization/lock.h"
+#include "base/third_party/dynamic_annotations/dynamic_annotations.h"
+#include "base/trace_event/trace_category.h"
+
+namespace base {
+namespace trace_event {
+
+namespace {
+
+constexpr size_t kMaxCategories = 200;
+const int kNumBuiltinCategories = 4;
+
+// |g_categories| might end up causing creating dynamic initializers if not POD.
+static_assert(std::is_pod<TraceCategory>::value, "TraceCategory must be POD");
+
+// These entries must be kept consistent with the kCategory* consts below.
+TraceCategory g_categories[kMaxCategories] = {
+    {0, 0, "tracing categories exhausted; must increase kMaxCategories"},
+    {0, 0, "tracing already shutdown"}, // See kCategoryAlreadyShutdown below.
+    {0, 0, "__metadata"},               // See kCategoryMetadata below.
+    {0, 0, "toplevel"},                 // Warmup the toplevel category.
+};
+
+base::subtle::AtomicWord g_category_index = kNumBuiltinCategories;
+
+base::LazyInstance<base::Lock>::Leaky g_category_lock =
+    LAZY_INSTANCE_INITIALIZER;
+
+bool IsValidCategoryPtr(const TraceCategory* category) {
+  // If any of these are hit, something has cached a corrupt category pointer.
+  uintptr_t ptr = reinterpret_cast<uintptr_t>(category);
+  return ptr % sizeof(void*) == 0 &&
+         ptr >= reinterpret_cast<uintptr_t>(&g_categories[0]) &&
+         ptr <= reinterpret_cast<uintptr_t>(&g_categories[kMaxCategories - 1]);
+}
+
+}  // namespace
+
+// static
+TraceCategory* const CategoryRegistry::kCategoryExhausted = &g_categories[0];
+TraceCategory* const CategoryRegistry::kCategoryAlreadyShutdown =
+    &g_categories[1];
+TraceCategory* const CategoryRegistry::kCategoryMetadata = &g_categories[2];
+
+// static
+void CategoryRegistry::Initialize() {
+  // Trace is enabled or disabled on one thread while other threads are
+  // accessing the enabled flag. We don't care whether edge-case events are
+  // traced or not, so we allow races on the enabled flag to keep the trace
+  // macros fast.
+  for (size_t i = 0; i < kMaxCategories; ++i) {
+    ANNOTATE_BENIGN_RACE(g_categories[i].state_ptr(),
+                         "trace_event category enabled");
+    // If this DCHECK is hit in a test it means that ResetForTesting() is not
+    // called and the categories state leaks between test fixtures.
+    DCHECK(!g_categories[i].is_enabled());
+  }
+}
+
+// static
+void CategoryRegistry::ResetForTesting() {
+  AutoLock lock(g_category_lock.Get());
+  for (size_t i = 0; i < kMaxCategories; ++i)
+    g_categories[i].reset_for_testing();
+}
+
+// static
+bool CategoryRegistry::GetOrCreateCategoryByName(const char* category_name,
+                                                 TraceCategory** category) {
+  DCHECK(!strchr(category_name, '"'))
+      << "Category names may not contain double quote";
+
+  // The g_categories is append only, avoid using a lock for the fast path.
+  size_t category_index = base::subtle::Acquire_Load(&g_category_index);
+
+  // Search for pre-existing category group.
+  for (size_t i = 0; i < category_index; ++i) {
+    if (strcmp(g_categories[i].name(), category_name) == 0) {
+      *category = &g_categories[i];
+      return false;
+    }
+  }
+
+  // This is the slow path: the lock is not held in the case above, so more
+  // than one thread could have reached here trying to add the same category.
+  // Only hold the lock when actually appending a new category, and check the
+  // categories groups again.
+  // TODO(primiano): there should be no need for the acquire/release semantics
+  // on g_category_index below, the outer lock implies that. Remove once the
+  // tracing refactoring reaches a quieter state and we can afford the risk.
+  AutoLock lock(g_category_lock.Get());
+  category_index = base::subtle::Acquire_Load(&g_category_index);
+  for (size_t i = 0; i < category_index; ++i) {
+    if (strcmp(g_categories[i].name(), category_name) == 0) {
+      *category = &g_categories[i];
+      return false;
+    }
+  }
+
+  // Create a new category.
+  if (category_index >= kMaxCategories) {
+    NOTREACHED() << "must increase kMaxCategories";
+    *category = kCategoryExhausted;
+    return false;
+  }
+
+  // TODO(primiano): this strdup should be removed. The only documented reason
+  // for it was TraceWatchEvent, which is gone. However, something might have
+  // ended up relying on this. Needs some auditing before removal.
+  const char* category_name_copy = strdup(category_name);
+  ANNOTATE_LEAKING_OBJECT_PTR(category_name_copy);
+
+  *category = &g_categories[category_index];
+  DCHECK(!(*category)->is_valid());
+  DCHECK(!(*category)->is_enabled());
+  (*category)->set_name(category_name_copy);
+
+  // Update the max index now.
+  base::subtle::Release_Store(&g_category_index, category_index + 1);
+  return true;
+}
+
+// static
+const TraceCategory* CategoryRegistry::GetCategoryByStatePtr(
+    const uint8_t* category_state) {
+  const TraceCategory* category = TraceCategory::FromStatePtr(category_state);
+  DCHECK(IsValidCategoryPtr(category));
+  return category;
+}
+
+// static
+bool CategoryRegistry::IsBuiltinCategory(const TraceCategory* category) {
+  DCHECK(IsValidCategoryPtr(category));
+  return category < &g_categories[kNumBuiltinCategories];
+}
+
+// static
+CategoryRegistry::Range CategoryRegistry::GetAllCategories() {
+  // The |g_categories| array is append only. We have to only guarantee to
+  // not return an index to a category which is being initialized by
+  // GetOrCreateCategoryByName().
+  size_t category_index = base::subtle::Acquire_Load(&g_category_index);
+  return CategoryRegistry::Range(&g_categories[0],
+                                 &g_categories[category_index]);
+}
+
+}  // namespace trace_event
+}  // namespace base