[Tracing] V8 Tracing Controller

src/libplatform/tracing/tracing-controller.cc

+// Copyright 2016 the V8 project 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 <stdio.h>
+#include <string.h>
+
+#include "include/libplatform/v8-tracing.h"
+
+#include "src/base/platform/mutex.h"
+
+namespace v8 {
+namespace platform {
+namespace tracing {
+
+#define MAX_CATEGORY_GROUPS 200
+
+// Parallel arrays g_category_groups and g_category_group_enabled are separate
+// so that a pointer to a member of g_category_group_enabled can be easily
+// converted to an index into g_category_groups. This allows macros to deal
+// only with char enabled pointers from g_category_group_enabled, and we can
+// convert internally to determine the category name from the char enabled
+// pointer.
+const char* g_category_groups[MAX_CATEGORY_GROUPS] = {
+    "toplevel", "tracing already shutdown",
+    "tracing categories exhausted; must increase MAX_CATEGORY_GROUPS",
+    "__metadata"};
+
+// The enabled flag is char instead of bool so that the API can be used from C.
+unsigned char g_category_group_enabled[MAX_CATEGORY_GROUPS] = {0};
+// Indexes here have to match the g_category_groups array indexes above.
+const int g_category_already_shutdown = 1;
+const int g_category_categories_exhausted = 2;
+// Metadata category not used in V8.
+// const int g_category_metadata = 3;
+const int g_num_builtin_categories = 4;
+
+// Skip default categories.
+v8::base::AtomicWord g_category_index = g_num_builtin_categories;
+
+void TracingController::Initialize(TraceBuffer* trace_buffer) {
+  trace_buffer_.reset(trace_buffer);
+}
+
+uint64_t TracingController::AddTraceEvent(
+    char phase, const uint8_t* category_enabled_flag, const char* name,
+    const char* scope, uint64_t id, uint64_t bind_id, int num_args,
+    const char** arg_names, const uint8_t* arg_types,
+    const uint64_t* arg_values, unsigned int flags) {
+  uint64_t handle;
+  TraceObject* trace_object = trace_buffer_->AddTraceEvent(&handle);
+  if (trace_object) {
+    trace_object->Initialize(
+        phase, std::string(name),
+        std::string(GetCategoryGroupName(category_enabled_flag)), id, bind_id,
+        num_args, flags);
+  }
+  return handle;
+}
+
+void TracingController::UpdateTraceEventDuration(
+    const uint8_t* category_enabled_flag, const char* name, uint64_t handle) {
+  TraceObject* trace_object = trace_buffer_->GetEventByHandle(handle);
+  if (!trace_object) return;
+  trace_object->UpdateDuration();
+}
+
+const uint8_t* TracingController::GetCategoryGroupEnabled(
+    const char* category_group) {
+  if (!trace_buffer_) {
+    DCHECK(!g_category_group_enabled[g_category_already_shutdown]);
+    return &g_category_group_enabled[g_category_already_shutdown];
+  }
+  return GetCategoryGroupEnabledInternal(category_group);
+}
+
+const char* TracingController::GetCategoryGroupName(
+    const uint8_t* category_group_enabled) {
+  // Calculate the index of the category group by finding
+  // category_group_enabled in g_category_group_enabled array.
+  uintptr_t category_begin =
+      reinterpret_cast<uintptr_t>(g_category_group_enabled);
+  uintptr_t category_ptr = reinterpret_cast<uintptr_t>(category_group_enabled);
+  // Check for out of bounds category pointers.
+  DCHECK(category_ptr >= category_begin &&
+         category_ptr < reinterpret_cast<uintptr_t>(g_category_group_enabled +
+                                                    MAX_CATEGORY_GROUPS));
+  uintptr_t category_index =
+      (category_ptr - category_begin) / sizeof(g_category_group_enabled[0]);
+  return g_category_groups[category_index];
+}
+
+void TracingController::StartTracing(TraceConfig* trace_config) {
+  trace_config_.reset(trace_config);
+  mode_ = RECORDING_MODE;
+  UpdateCategoryGroupEnabledFlags();
+}
+
+void TracingController::StopTracing() {
+  trace_buffer_->Flush();
+  mode_ = DISABLED;
+  UpdateCategoryGroupEnabledFlags();

[mattloring, 2016/07/15 00:19:01]

Move this before Flush to disable more traces before flushing.

[fmeawad, 2016/07/15 21:21:58]

Done.

+}
+
+void TracingController::UpdateCategoryGroupEnabledFlag(size_t category_index) {
+  unsigned char enabled_flag = 0;
+  const char* category_group = g_category_groups[category_index];
+  if (mode_ == RECORDING_MODE &&
+      trace_config_->IsCategoryGroupEnabled(category_group)) {
+    enabled_flag |= ENABLED_FOR_RECORDING;
+  }
+
+  // TODO(fmeawad): EventCallback and ETW modes are not yet supported in V8.
+  // TODO(primiano): this is a temporary workaround for catapult:#2341,
+  // to guarantee that metadata events are always added even if the category
+  // filter is "-*". See crbug.com/618054 for more details and long-term fix.
+  if (mode_ == RECORDING_MODE && !strcmp(category_group, "__metadata")) {
+    enabled_flag |= ENABLED_FOR_RECORDING;
+  }
+
+  g_category_group_enabled[category_index] = enabled_flag;
+}
+
+void TracingController::UpdateCategoryGroupEnabledFlags() {
+  size_t category_index = base::NoBarrier_Load(&g_category_index);
+  for (size_t i = 0; i < category_index; i++) UpdateCategoryGroupEnabledFlag(i);
+}
+
+const uint8_t* TracingController::GetCategoryGroupEnabledInternal(
+    const char* category_group) {
+  // Check that category groups does not contain double quote
+  DCHECK(!strchr(category_group, '"'));
+
+  // The g_category_groups is append only, avoid using a lock for the fast path.
+  size_t current_category_index = v8::base::Acquire_Load(&g_category_index);
+
+  // Search for pre-existing category group.
+  for (size_t i = 0; i < current_category_index; ++i) {
+    if (strcmp(g_category_groups[i], category_group) == 0) {
+      return &g_category_group_enabled[i];
+    }
+  }
+
+  unsigned char* category_group_enabled = NULL;
+  size_t category_index = base::Acquire_Load(&g_category_index);
+  for (size_t i = 0; i < category_index; ++i) {
+    if (strcmp(g_category_groups[i], category_group) == 0) {
+      return &g_category_group_enabled[i];
+    }
+  }
+
+  // Create a new category group.
+  // Check that there is a slot for the new category_group.
+  DCHECK(category_index < MAX_CATEGORY_GROUPS);
+  if (category_index < MAX_CATEGORY_GROUPS) {
+    // Don't hold on to the category_group pointer, so that we can create
+    // category groups with strings not known at compile time (this is
+    // required by SetWatchEvent).
+    const char* new_group = strdup(category_group);
+    g_category_groups[category_index] = new_group;
+    DCHECK(!g_category_group_enabled[category_index]);
+    // Note that if both included and excluded patterns in the
+    // TraceConfig are empty, we exclude nothing,
+    // thereby enabling this category group.
+    UpdateCategoryGroupEnabledFlag(category_index);
+    category_group_enabled = &g_category_group_enabled[category_index];
+    // Update the max index now.
+    base::Release_Store(&g_category_index, category_index + 1);
+  } else {
+    category_group_enabled =
+        &g_category_group_enabled[g_category_categories_exhausted];
+  }
+  return category_group_enabled;
+}
+
+}  // namespace tracing
+}  // namespace platform
+}  // namespace v8