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// 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.
#ifndef BASE_TRACE_EVENT_TRACING_AGENT_H_
#define BASE_TRACE_EVENT_TRACING_AGENT_H_
#include "base/base_export.h"
#include "base/callback.h"
#include "base/memory/ref_counted_memory.h"
#include "base/values.h"
namespace base {
class TimeTicks;
namespace trace_event {
class TraceConfig;
// A tracing agent is an entity that records its own sort of trace. Each
// tracing method that produces its own trace log should implement this
// interface. All tracing agents must only be controlled by TracingController.
// Some existing examples include TracingControllerImpl for Chrome trace events,
// DebugDaemonClient for CrOs system trace, EtwSystemEventConsumer for Windows
// system trace and PowerTracingAgent for BattOr power trace.
class BASE_EXPORT TracingAgent {
public:
using StopAgentTracingCallback = base::Callback<void(
const std::string& agent_name,
const std::string& events_label,
const scoped_refptr<base::RefCountedString>& events_str_ptr)>;
using RecordClockSyncMarkerCallback = base::Callback<void(
int sync_id,
const TimeTicks& issue_ts,
const TimeTicks& issue_end_ts)>;
virtual ~TracingAgent();
// Gets the name of the tracing agent. Each tracing agent's name should be
// unique.
virtual std::string GetTracingAgentName() = 0;
// Gets the trace event label of this tracing agent. The label will be used to
// label this agent's trace when all traces from different tracing agents are
// combined. Multiple tracing agents could have the same label. The tracing
// agents using the same label should not be able to run at the same time. For
// example, ETW on Windows and CrOS system tracing both use
// "systemTraceEvents" as the label. Those two agents never run at the same
// time because they are for different platforms.
virtual std::string GetTraceEventLabel() = 0;
// Starts tracing on the tracing agent with the trace configuration.
virtual bool StartAgentTracing(const TraceConfig& trace_config) = 0;
// Stops tracing on the tracing agent. The trace data will be passed back to
// the TracingController via the callback.
virtual void StopAgentTracing(const StopAgentTracingCallback& callback) = 0;
// Checks if the tracing agent supports explicit clock synchronization.
virtual bool SupportsExplicitClockSync();
// Records a clock sync marker issued by another tracing agent. This is only
// used if the tracing agent supports explicit clock synchronization.
//
// Two things need to be done:
// 1. The issuer asks the receiver to record the clock sync marker.
// 2. The issuer records how long the receiver takes to do the recording.
//
// In Chrome, the receiver thread also runs in Chrome and it will talk to the
// real receiver entity, e.g., power monitor or Android device system, via
// different communication methods, e.g., through USB or file reading/writing.
// The 2nd task measures that communication latency.
//
// Having a reliable timing measurement for the 2nd task requires synchronous
// function call without any cross-thread or cross-process activity. However,
// tracing agents in Chrome run in their own threads. Therefore, the issuer
// needs to dedicate the 2nd task to the receiver to take time measurements
// in the receiver thread, and the receiver thread needs to pass them back to
// the issuer in the callback.
//
// The assumption is that the receiver thread knows the issuer's clock, which
// is true in Chrome because all agent threads' clocks are Chrome clock.
virtual void RecordClockSyncMarker(
int sync_id,
const RecordClockSyncMarkerCallback& callback);
};
} // namespace trace_event
} // namespace base
#endif // BASE_TRACE_EVENT_TRACING_AGENT_H_
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