react-native/docs/systrace.md

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Methods

• installReactHook
• setEnabled
• isEnabled
• beginEvent
• endEvent
• beginAsyncEvent
• endAsyncEvent
• counterEvent
• attachToRelayProfiler
• swizzleJSON
• measureMethods
• measure

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Reference

Methods

installReactHook()

static installReactHook(useFiber)

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setEnabled()

static setEnabled(enabled)

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isEnabled()

static isEnabled()

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beginEvent()

static beginEvent(profileName?, args?)

beginEvent/endEvent for starting and then ending a profile within the same call stack frame

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endEvent()

static endEvent()

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beginAsyncEvent()

static beginAsyncEvent(profileName?)

beginAsyncEvent/endAsyncEvent for starting and then ending a profile where the end can either occur on another thread or out of the current stack frame, eg await the returned cookie variable should be used as input into the endAsyncEvent call to end the profile

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endAsyncEvent()

static endAsyncEvent(profileName?, cookie?)

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counterEvent()

static counterEvent(profileName?, value?)

counterEvent registers the value to the profileName on the systrace timeline

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attachToRelayProfiler()

static attachToRelayProfiler(relayProfiler)

Relay profiles use await calls, so likely occur out of current stack frame therefore async variant of profiling is used

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swizzleJSON()

static swizzleJSON()

This is not called by default due to perf overhead but it's useful if you want to find traces which spend too much time in JSON.

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measureMethods()

static measureMethods(object, objectName, methodNames)

Measures multiple methods of a class. For example, you can do:

Systrace.measureMethods(JSON, 'JSON', ['parse', 'stringify']);

Parameters:

Name	Type	Required	Description
object	any	Yes
objectName	string	Yes
methodNames	array	Yes	Map from method names to method display names.

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measure()

static measure(objName, fnName, func)

Returns an profiled version of the input function. For example, you can:

JSON.parse = Systrace.measure('JSON', 'parse', JSON.parse);

Parameters:

Name	Type	Required	Description
objName	string	Yes
fnName	string	Yes
func	function	Yes