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| 1 // Copyright 2015 The Chromium Authors. All rights reserved. |
| 2 // Use of this source code is governed by a BSD-style license that can be |
| 3 // found in the LICENSE file. |
| 4 |
| 5 #ifndef BASE_TRACE_EVENT_TRACING_AGENT_H_ |
| 6 #define BASE_TRACE_EVENT_TRACING_AGENT_H_ |
| 7 |
| 8 #include "base/base_export.h" |
| 9 #include "base/callback.h" |
| 10 #include "base/memory/ref_counted_memory.h" |
| 11 #include "base/values.h" |
| 12 |
| 13 namespace base { |
| 14 |
| 15 class TimeTicks; |
| 16 |
| 17 namespace trace_event { |
| 18 |
| 19 class TraceConfig; |
| 20 |
| 21 // A tracing agent is an entity that records its own sort of trace. Each |
| 22 // tracing method that produces its own trace log should implement this |
| 23 // interface. All tracing agents must only be controlled by TracingController. |
| 24 // Some existing examples include TracingControllerImpl for Chrome trace events, |
| 25 // DebugDaemonClient for CrOs system trace, EtwSystemEventConsumer for Windows |
| 26 // system trace and PowerTracingAgent for BattOr power trace. |
| 27 class BASE_EXPORT TracingAgent { |
| 28 public: |
| 29 using StopAgentTracingCallback = base::Callback<void( |
| 30 const std::string& agent_name, |
| 31 const std::string& events_label, |
| 32 const scoped_refptr<base::RefCountedString>& events_str_ptr)>; |
| 33 using RecordClockSyncMarkerCallback = base::Callback<void( |
| 34 int sync_id, |
| 35 const TimeTicks& sync_ts, |
| 36 const TimeTicks& sync_end_ts)>; |
| 37 |
| 38 virtual ~TracingAgent(); |
| 39 |
| 40 // Gets the name of the tracing agent. Each tracing agent's name should be |
| 41 // unique. |
| 42 virtual std::string GetTracingAgentName() = 0; |
| 43 |
| 44 // Gets the trace event label of this tracing agent. The label will be used to |
| 45 // label this agent's trace when all traces from different tracing agents are |
| 46 // combined. Multiple tracing agents could have the same label. The tracing |
| 47 // agents using the same label should not be able to run at the same time. For |
| 48 // example, ETW on Windows and CrOS system tracing both use |
| 49 // "systemTraceEvents" as the label. Those two agents never run at the same |
| 50 // time because they are for different platforms. |
| 51 virtual std::string GetTraceEventLabel() = 0; |
| 52 |
| 53 // Starts tracing on the tracing agent with the trace configuration. |
| 54 virtual bool StartAgentTracing(const TraceConfig& trace_config) = 0; |
| 55 |
| 56 // Stops tracing on the tracing agent. The trace data will be passed back to |
| 57 // the TracingController via the callback. |
| 58 virtual void StopAgentTracing(const StopAgentTracingCallback& callback) = 0; |
| 59 |
| 60 // Checks if the tracing agent supports explicit clock synchronization. |
| 61 virtual bool SupportsExplicitClockSync(); |
| 62 |
| 63 // Records a clock sync marker issued by another tracing agent. This is only |
| 64 // used if the tracing agent supports explicit clock synchronization. |
| 65 // |
| 66 // Two things need to be done: |
| 67 // 1. The issuer asks the receiver to record the clock sync marker. |
| 68 // 2. The issuer records how long the receiver takes to do the recording. |
| 69 // |
| 70 // In Chrome, the receiver thread also runs in Chrome and it will talk to the |
| 71 // real receiver entity, e.g., power monitor or Android device system, via |
| 72 // different communication methods, e.g., through USB or file reading/writing. |
| 73 // The 2nd task measures that communication latency. |
| 74 // |
| 75 // Having a reliable timing measurement for the 2nd task requires synchronous |
| 76 // function call without any cross-thread or cross-process activity. However, |
| 77 // tracing agents in Chrome run in their own threads. Therefore, the issuer |
| 78 // needs to dedicate the 2nd task to the receiver to take time measurements |
| 79 // in the receiver thread, and the receiver thread needs to pass them back to |
| 80 // the issuer in the callback. |
| 81 // |
| 82 // The assumption is that the receiver thread knows the issuer's clock, which |
| 83 // is true in Chrome because all agent threads' clocks are Chrome clock. |
| 84 virtual void RecordClockSyncMarker( |
| 85 int sync_id, |
| 86 const RecordClockSyncMarkerCallback& callback); |
| 87 }; |
| 88 |
| 89 } // namespace trace_event |
| 90 } // namespace base |
| 91 |
| 92 #endif // BASE_TRACE_EVENT_TRACING_AGENT_H_ |
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