以應用程式為導向的剖析

@RequiresApi(Build.VERSION_CODES.VANILLA_ICE_CREAM)
@Composable
fun ProfiledScreen(modifier: Modifier = Modifier) {
    // Use the application context: requestProfiling resolves the ProfilingManager
    // system service from it, so there's no reason to hand it a short-lived Activity.
    val appContext = LocalContext.current.applicationContext
    val scope = rememberCoroutineScope()

    Button(
        onClick = {
            // Run the orchestration off the main thread. Profiling a heavy operation
            // on the UI thread would freeze the UI (ANR) and distort the very metrics
            // you're trying to capture.
            //
            // Note: this scope is tied to composition. If the user leaves this screen
            // mid-session, the coroutine is cancelled and stopSignal.cancel() might not
            // run, but setDurationMs() acts as a safety net and ends the trace.
            scope.launch(Dispatchers.Default) {
                val callbackExecutor = Dispatchers.IO.asExecutor()
                val resultCallback = Consumer<ProfilingResult> { profilingResult ->
                    if (profilingResult.errorCode == ProfilingResult.ERROR_NONE) {
                        Log.d("ProfileTest", "Result file: ${profilingResult.resultFilePath}")
                    } else {
                        // errorMessage explains the failure (e.g., rate limiting); keep it.
                        Log.e(
                            "ProfileTest",
                            "Profiling failed errorCode=${profilingResult.errorCode} " +
                                "errorMessage=${profilingResult.errorMessage}"
                        )
                    }
                }

                val stopSignal = CancellationSignal()
                val requestBuilder = SystemTraceRequestBuilder().apply {
                    setCancellationSignal(stopSignal)
                    setTag("FOO") // Caller-supplied tag for identification.
                    setDurationMs(60000) // Hard cap: ends the session if cancel() never fires.
                    setBufferFillPolicy(BufferFillPolicy.RING_BUFFER)
                    setBufferSizeKb(32768)
                }

                // 1. Start the session. This is asynchronous system IPC. The tracing
                //    engine takes a moment to start and allocate buffers.
                requestProfiling(appContext, requestBuilder.build(), callbackExecutor, resultCallback)

                // 2. The API exposes no "profiling started" signal, so pad with a short,
                //    best-effort delay before running the code you care about. This is
                //    approximate. Increase it on slower or heavily loaded devices.
                delay(STARTUP_PADDING_MS)

                // 3. The session is already recording every thread in your app. This slice
                //    doesn't scope what's captured. It just labels this region of the
                //    timeline so heavyOperation() is easier to find. trace { } closes the
                //    section even if the block throws.

                trace("MyApp:HeavyOperation") {
                    heavyOperation()
                }

                // 4. Stop recording. Until this fires or the setDurationMs() cap is
                //    reached (whichever comes first), the session keeps capturing app-wide
                //    activity.

                stopSignal.cancel()
            }
        }
    ) {
        Text("Run & Profile Heavy Operation")
    }
}

// Best-effort wait for the system trace engine to initialize before profiling.
// There is no deterministic start callback; tune this for your target devices.
private const val STARTUP_PADDING_MS = 100L

fun heavyOperation() {
    // Background computations to profile.
}

void heavyOperation() {
  // Computations you want to profile
}

void sampleRecordSystemTrace() {
  Executor mainExecutor = Executors.newSingleThreadExecutor();
  Consumer<ProfilingResult> resultCallback =
      new Consumer<ProfilingResult>() {
        @Override
        public void accept(ProfilingResult profilingResult) {
          if (profilingResult.getErrorCode() == ProfilingResult.ERROR_NONE) {
            Log.d(
                "ProfileTest",
                "Received profiling result file=" + profilingResult.getResultFilePath());
            setupProfileUploadWorker(profilingResult.getResultFilePath());
          } else {
            Log.e(
                "ProfileTest",
                "Profiling failed errorcode="

                    + profilingResult.getErrorCode()
                    + " errormsg="
                    + profilingResult.getErrorMessage());
          }
        }
      };
  CancellationSignal stopSignal = new CancellationSignal();

  SystemTraceRequestBuilder requestBuilder = new SystemTraceRequestBuilder();
  requestBuilder.setCancellationSignal(stopSignal);
  requestBuilder.setTag("FOO");
  requestBuilder.setDurationMs(60000);
  requestBuilder.setBufferFillPolicy(BufferFillPolicy.RING_BUFFER);
  requestBuilder.setBufferSizeKb(32768);
  Profiling.requestProfiling(getApplicationContext(), requestBuilder.build(), mainExecutor,
      resultCallback);

  // Wait some time for profiling to start.

  Trace.beginSection("MyApp:HeavyOperation");
  heavyOperation();
  Trace.endSection();

  // Once the interesting code section is profiled, stop profile
  stopSignal.cancel();
}