97 lines
4.2 KiB
C++
97 lines
4.2 KiB
C++
// Copyright 2015 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_TRACE_EVENT_TRACING_AGENT_H_
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#define BASE_TRACE_EVENT_TRACING_AGENT_H_
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#include "base/base_export.h"
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#include "base/callback.h"
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#include "base/memory/ref_counted_memory.h"
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#include "base/values.h"
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namespace base {
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class TimeTicks;
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namespace trace_event {
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class TraceConfig;
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// A tracing agent is an entity that records its own sort of trace. Each
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// tracing method that produces its own trace log should implement this
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// interface. All tracing agents must only be controlled by TracingController.
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// Some existing examples include TracingControllerImpl for Chrome trace events,
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// DebugDaemonClient for CrOs system trace, and EtwTracingAgent for Windows
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// system.
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class BASE_EXPORT TracingAgent {
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public:
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using StartAgentTracingCallback =
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base::OnceCallback<void(const std::string& agent_name, bool success)>;
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// Passing a null or empty events_str_ptr indicates that no trace data is
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// available for the specified agent.
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using StopAgentTracingCallback = base::OnceCallback<void(
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const std::string& agent_name,
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const std::string& events_label,
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const scoped_refptr<base::RefCountedString>& events_str_ptr)>;
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using RecordClockSyncMarkerCallback =
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base::OnceCallback<void(const std::string& sync_id,
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const TimeTicks& issue_ts,
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const TimeTicks& issue_end_ts)>;
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virtual ~TracingAgent();
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// Gets the name of the tracing agent. Each tracing agent's name should be
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// unique.
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virtual std::string GetTracingAgentName() = 0;
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// Gets the trace event label of this tracing agent. The label will be used to
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// label this agent's trace when all traces from different tracing agents are
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// combined. Multiple tracing agents could have the same label. The tracing
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// agents using the same label should not be able to run at the same time. For
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// example, ETW on Windows and CrOS system tracing both use
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// "systemTraceEvents" as the label. Those two agents never run at the same
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// time because they are for different platforms.
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virtual std::string GetTraceEventLabel() = 0;
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// Starts tracing on the tracing agent with the trace configuration.
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virtual void StartAgentTracing(const TraceConfig& trace_config,
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StartAgentTracingCallback callback) = 0;
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// Stops tracing on the tracing agent. The trace data will be passed back to
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// the TracingController via the callback.
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virtual void StopAgentTracing(StopAgentTracingCallback callback) = 0;
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// Checks if the tracing agent supports explicit clock synchronization.
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virtual bool SupportsExplicitClockSync();
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// Records a clock sync marker issued by another tracing agent. This is only
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// used if the tracing agent supports explicit clock synchronization.
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//
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// Two things need to be done:
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// 1. The issuer asks the receiver to record the clock sync marker.
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// 2. The issuer records how long the receiver takes to do the recording.
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//
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// In Chrome, the receiver thread also runs in Chrome and it will talk to the
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// real receiver entity, e.g., power monitor or Android device system, via
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// different communication methods, e.g., through USB or file reading/writing.
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// The 2nd task measures that communication latency.
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//
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// Having a reliable timing measurement for the 2nd task requires synchronous
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// function call without any cross-thread or cross-process activity. However,
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// tracing agents in Chrome run in their own threads. Therefore, the issuer
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// needs to dedicate the 2nd task to the receiver to take time measurements
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// in the receiver thread, and the receiver thread needs to pass them back to
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// the issuer in the callback.
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//
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// The assumption is that the receiver thread knows the issuer's clock, which
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// is true in Chrome because all agent threads' clocks are Chrome clock.
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virtual void RecordClockSyncMarker(const std::string& sync_id,
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RecordClockSyncMarkerCallback callback);
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};
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} // namespace trace_event
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} // namespace base
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#endif // BASE_TRACE_EVENT_TRACING_AGENT_H_
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