Systrace #

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

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

counterEvent registers the value to the profileName on the systrace timeline

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

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.

Measures multiple methods of a class. For example, you can do: Systrace.measureMethods(JSON, 'JSON', ['parse', 'stringify']);

@param object @param objectName @param methodNames Map from method names to method display names.

Returns an profiled version of the input function. For example, you can: JSON.parse = Systrace.measure('JSON', 'parse', JSON.parse);

@param objName @param fnName @param {function} func @return {function} replacement function