Slow Reports - Add message filter to trigger background traces from child processes.

content/browser/tracing/background_tracing_manager_impl.cc

Index: content/browser/tracing/background_tracing_manager_impl.cc
diff --git a/content/browser/tracing/background_tracing_manager_impl.cc b/content/browser/tracing/background_tracing_manager_impl.cc
index 68392b2c1e9f798b933b288169b672efb173426c..8acad9ef5e805242294b7382698c4d68b375adf1 100644
--- a/content/browser/tracing/background_tracing_manager_impl.cc
+++ b/content/browser/tracing/background_tracing_manager_impl.cc
@@ -9,6 +9,8 @@
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/statistics_recorder.h"
 #include "base/time/time.h"
+#include "components/tracing/tracing_messages.h"
+#include "content/browser/tracing/trace_message_filter.h"
 #include "content/public/browser/background_tracing_preemptive_config.h"
 #include "content/public/browser/background_tracing_reactive_config.h"
 #include "content/public/browser/browser_thread.h"
@@ -82,17 +84,31 @@ BackgroundTracingManagerImpl* BackgroundTracingManagerImpl::GetInstance() {
 }
 
 BackgroundTracingManagerImpl::BackgroundTracingManagerImpl()
-    : delegate_(GetContentClient()->browser()->GetTracingDelegate()),
-      is_gathering_(false),
+    : is_gathering_(false),
       is_tracing_(false),
       requires_anonymized_data_(true),
       trigger_handle_ids_(0) {
+  CreateDelegate();
 }
 
 BackgroundTracingManagerImpl::~BackgroundTracingManagerImpl() {
   NOTREACHED();
 }
 
+void BackgroundTracingManagerImpl::CreateDelegate() {
+  // The delegate must be instantiated on the UI thread, so if the
+  // first access to the BackgroundTracingManagerImpl is from another thread

[oystein (OOO til 10th of July), 2015/07/21 20:52:45]

When does this happen? Can we be sure there's no race conditions here, if the
BackgroundTracingManagerImpl can be lazily instantiated on multiple threads?

[shatch, 2015/07/22 17:44:13]

This happened in a few tests where the message filter called in to add a filter,
but I think this is unnecessary now if we're piggybacking on the trace message
filter, which does some checks before adding the filter.

LazyInstance guarantees thread safety for creation.

+  // we'll need to defer initializing it.
+  if (!content::BrowserThread::CurrentlyOn(content::BrowserThread::UI)) {
+    content::BrowserThread::PostTask(
+        content::BrowserThread::UI, FROM_HERE,
+        base::Bind(&BackgroundTracingManagerImpl::CreateDelegate,
+                   base::Unretained(this)));
+    return;
+  }
+  delegate_.reset(GetContentClient()->browser()->GetTracingDelegate());
+}
+
 void BackgroundTracingManagerImpl::WhenIdle(
     base::Callback<void()> idle_callback) {
   CHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
@@ -160,38 +176,58 @@ void BackgroundTracingManagerImpl::SetupUMACallbacks(
     } else {
       base::StatisticsRecorder::SetCallback(
           configs[i].histogram_trigger_info.histogram_name,
-          base::Bind(&BackgroundTracingManagerImpl::OnHistogramChanged,
+          base::Bind(&BackgroundTracingManagerImpl::OnHistogramChangedCallback,
                      base::Unretained(this),
                      configs[i].histogram_trigger_info.histogram_name,
                      configs[i].histogram_trigger_info.histogram_value));
     }
   }
+
+  SetupFiltersFromConfig(mode);
 }
 
-void BackgroundTracingManagerImpl::OnHistogramChanged(
-    const std::string& histogram_name,
-    base::Histogram::Sample reference_value,
-    base::Histogram::Sample actual_value) {
+void BackgroundTracingManagerImpl::OnHistogramTrigger(
+    const std::string& histogram_name) {
   if (!content::BrowserThread::CurrentlyOn(content::BrowserThread::UI)) {
     content::BrowserThread::PostTask(
         content::BrowserThread::UI, FROM_HERE,
-        base::Bind(&BackgroundTracingManagerImpl::OnHistogramChanged,
-                   base::Unretained(this), histogram_name, reference_value,
-                   actual_value));
+        base::Bind(&BackgroundTracingManagerImpl::OnHistogramTrigger,
+                   base::Unretained(this), histogram_name));
     return;
   }
 
   CHECK(config_ &&
         config_->mode == BackgroundTracingConfig::PREEMPTIVE_TRACING_MODE);
 
-  if (reference_value > actual_value)
+  if (!is_tracing_ || is_gathering_)
     return;
 
-  if (!is_tracing_ || is_gathering_)
+  BackgroundTracingPreemptiveConfig* preemptive_config =
+      static_cast<BackgroundTracingPreemptiveConfig*>(config_.get());
+  const std::vector<BackgroundTracingPreemptiveConfig::MonitoringRule>&
+      configs = preemptive_config->configs;
+  for (size_t i = 0; i < configs.size(); ++i) {
+    if (configs[i].type !=
+        BackgroundTracingPreemptiveConfig::
+            MONITOR_AND_DUMP_WHEN_SPECIFIC_HISTOGRAM_AND_VALUE) {
+      continue;
+    }
+
+    if (configs[i].histogram_trigger_info.histogram_name == histogram_name) {
+      RecordBackgroundTracingMetric(PREEMPTIVE_TRIGGERED);
+      BeginFinalizing(StartedFinalizingCallback());
+    }
+  }
+}
+
+void BackgroundTracingManagerImpl::OnHistogramChangedCallback(
+    const std::string& histogram_name,
+    base::Histogram::Sample reference_value,
+    base::Histogram::Sample actual_value) {
+  if (reference_value > actual_value)
     return;
 
-  RecordBackgroundTracingMetric(PREEMPTIVE_TRIGGERED);
-  BeginFinalizing(StartedFinalizingCallback());
+  OnHistogramTrigger(histogram_name);
 }
 
 bool BackgroundTracingManagerImpl::SetActiveScenario(
@@ -248,6 +284,70 @@ bool BackgroundTracingManagerImpl::HasActiveScenarioForTesting() {
   return config_;
 }
 
+void BackgroundTracingManagerImpl::AddFilter(
+    scoped_refptr<TraceMessageFilter> filter) {
+  if (!content::BrowserThread::CurrentlyOn(content::BrowserThread::UI)) {

[oystein (OOO til 10th of July), 2015/07/21 20:52:45]

Which threads can this be called on? Wouldn't this be consistent?

[shatch, 2015/07/22 17:44:13]

Called via OnChildSupportsTracing from the TraceMessageFtiler on the IO thread.
Moot if we reuse the filters from TracingControllerImpl.

+    content::BrowserThread::PostTask(
+        content::BrowserThread::UI, FROM_HERE,
+        base::Bind(&BackgroundTracingManagerImpl::AddFilter,
+                   base::Unretained(this), filter));
+    return;
+  }
+
+  filters_.insert(filter);
+  SetupFilterFromConfig(filter, BIND_CALLBACKS);
+}
+
+void BackgroundTracingManagerImpl::RemoveFilter(
+    scoped_refptr<TraceMessageFilter> filter) {
+  if (!content::BrowserThread::CurrentlyOn(content::BrowserThread::UI)) {

[oystein (OOO til 10th of July), 2015/07/21 20:52:45]

Same thread question as AddFilter

+    content::BrowserThread::PostTask(
+        content::BrowserThread::UI, FROM_HERE,
+        base::Bind(&BackgroundTracingManagerImpl::RemoveFilter,
+                   base::Unretained(this), filter));
+    return;
+  }
+
+  filters_.erase(filter);
+}
+
+void BackgroundTracingManagerImpl::SetupFiltersFromConfig(
+    BackgroundTracingManagerImpl::SetupUMACallMode mode) {
+  for (auto it = filters_.begin(); it != filters_.end(); ++it)
+    SetupFilterFromConfig(*it, mode);
+}
+
+void BackgroundTracingManagerImpl::SetupFilterFromConfig(
+    scoped_refptr<TraceMessageFilter> filter,
+    BackgroundTracingManagerImpl::SetupUMACallMode mode) {
+  if (!config_ ||
+      config_->mode != BackgroundTracingConfig::PREEMPTIVE_TRACING_MODE)
+    return;
+
+  BackgroundTracingPreemptiveConfig* preemptive_config =
+      static_cast<BackgroundTracingPreemptiveConfig*>(config_.get());
+
+  const std::vector<BackgroundTracingPreemptiveConfig::MonitoringRule>&
+      configs = preemptive_config->configs;
+
+  for (size_t i = 0; i < configs.size(); ++i) {
+    if (configs[i].type !=
+        BackgroundTracingPreemptiveConfig::
+            MONITOR_AND_DUMP_WHEN_SPECIFIC_HISTOGRAM_AND_VALUE) {
+      continue;
+    }
+
+    if (mode == CLEAR_CALLBACKS) {
+      filter->Send(new TracingMsg_ClearUMACallback(
+          configs[i].histogram_trigger_info.histogram_name));
+    } else {
+      filter->Send(new TracingMsg_SetUMACallback(
+          configs[i].histogram_trigger_info.histogram_name,
+          configs[i].histogram_trigger_info.histogram_value));
+    }
+  }
+}
+
 void BackgroundTracingManagerImpl::ValidateStartupScenario() {
   if (!config_ || !delegate_)
     return;
@@ -518,6 +618,8 @@ void BackgroundTracingManagerImpl::BeginFinalizing(
 }
 
 void BackgroundTracingManagerImpl::AbortScenario() {
+  SetupUMACallbacks(CLEAR_CALLBACKS);
+
   is_tracing_ = false;
   config_.reset();