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µinstrument.hx

Micro framework for Haxe instrumentation

  1. A visual example
  2. Tracing calls and arguments
    2.1. Debugging database requests
  3. Timing calls
  4. Customizing the callbacks
  5. Advanced instrumentation
  6. Notes

A visual example

// Basic.hx
class Basic {
	public static function main()
	{
		trace(haxe.Json.parse('{ "value" : 33.3 }'));
	}
}
# basic.hxml
-neko basic.n
-main Basic
-lib uinstrument
--macro uinstrument.TimeCalls.hijack("haxe.Json", "parse")
--macro uinstrument.TraceCalls.hijack("haxe.format.JsonParser")
--macro uinstrument.TraceArgs.hijack("Std", "parseFloat")
--macro uinstrument.TraceArgs.hijack("Std", "int")
$ haxe basic.hxml
uinstrument/Instrument.hx:29: characters 72-74 : Warning : Removing AInline access from haxe.Json.parse

$ neko basic.n
CALL haxe.format.JsonParser.new
CALL haxe.format.JsonParser.parseRec
CALL haxe.format.JsonParser.parseString
CALL haxe.format.JsonParser.parseRec
CALL Std.parseFloat(x=<33.3>)
CALL Std.int(x=<33.3>)
TIME 186μs on haxe.Json.parse
Basic.hx:4: { value => 33.3 }

Tracing calls and arguments

For simple call tracing, it's enough to use uinstrument.TraceCalls.hijack(<class name>, ?<method name>). This will adapt the desired methods to call uinstrument.TraceCalls.onCalled at their beginning.

# basic.hxml
-neko basic.n
-main Basic
-lib uinstrument
--macro uinstrument.TraceCalls.hijack("haxe.format.JsonParser")
$ haxe basic.hxml
uinstrument/Instrument.hx:29: characters 72-74 : Warning : Removing AInline access from haxe.Json.parse

$ neko basic.n
CALL haxe.format.JsonParser.new
CALL haxe.format.JsonParser.parseRec
CALL haxe.format.JsonParser.parseString
CALL haxe.format.JsonParser.parseRec
Basic.hx:4: { value => 33.3 }

If, on the other hand, inspection of the arguments is desired, TraceCalls should be replaced by TraceArgs: this will instead call its onCalled function with an extra args:Array<{ name:String, value:Dynamic }> array.

# basic.hxml
-neko basic.n
-main Basic
-lib uinstrument
--macro uinstrument.TraceArgs.hijack("Std", "parseFloat")
--macro uinstrument.TraceArgs.hijack("Std", "int")
$ haxe basic.hxml
uinstrument/Instrument.hx:29: characters 72-74 : Warning : Removing AInline access from haxe.Json.parse

$ neko basic.n
CALL Std.parseFloat(x=<33.3>)
CALL Std.int(x=<33.3>)
Basic.hx:4: { value => 33.3 }

Note that TraceCalls.onCalled and TraceArgs.onCalled are dynamic functions and can be replaced at runtime: see Customizing the callbacks: tracing call stacks.

Debugging database requests

Tracing calls and arguments can be used to debug database requests, which can be particularly helpful when a project uses record-macros.

-lib uinstrument
--macro uinstrument.TraceArgs.hijack("sys.db.Sqlite.SqliteConnection", "request")
--macro uinstrument.TraceArgs.hijack("sys.db.Mysql.MysqlConnection", "request")

(You probably do not want to leave this on in production; at the very least make sure to sanitize the output so no sensitive information ever gets stored in log files).

Timing calls

Similar to call and argument tracing, uinstrument.TimeCalls.hijack(<class name>, ?<method name>) can be used to track the amount of time spent in some functions of interest.

By default the time spent is traced for every call, but customizing the callback by replacing TimeCalls.onTime allows these results to be manipulated freely, for example for aggregation or plotting.

# basic.hxml
-neko basic.n
-main Basic
-lib uinstrument
--macro uinstrument.TimeCalls.hijack("haxe.Json", "parse")
$ haxe basic.hxml
uinstrument/Instrument.hx:29: characters 72-74 : Warning : Removing AInline access from haxe.Json.parse

$ neko basic.n
TIME 186μs on haxe.Json.parse
Basic.hx:4: { value => 33.3 }

Customizing the callbacks

As alluded before, it is possible to replace the callbacks from TraceCalls, TraceArgs and TimeCalls with arbitrary functions.

For a simple example, let us include part of the stack when tracing each call.

// CallStacks.hx
import uinstrument.Tools.defaultTrace in itrace;

class CallStacks {
	static function onCalled(?pos:haxe.PosInfos)
	{
		itrace('CALL ${pos.className}.${pos.methodName}', pos);

		// remove onCalled and the instrumented function, and limit the
		// number of call stack items to display to two
		var cs = haxe.CallStack.callStack();
		var pcs = cs.slice(2, 4);
		for (i in haxe.CallStack.toString(pcs).split("\n")) {
			if (StringTools.trim(i) != "")
				itrace(' └╴ $i', pos);
		}
		var ommited = cs.length - pcs.length - 2;
		if (ommited > 0)
			itrace('    [$ommited ommited]', pos);
	}

	static function main()
	{
		uinstrument.TraceCalls.onCalled = onCalled;
		trace(haxe.Json.parse('{ "value" : 33.3 }'));
	}
}
# call_stacks.hxml
-neko call_stacks.n
-main CallStacks
-lib uinstrument
--macro uinstrument.TraceCalls.hijack("Std")
$ haxe call_stacks.hxml

$ neko call_stacks.n
CALL Std.__init__
CALL Std.parseFloat
 └╴ Called from /usr/local/share/haxe/std/haxe/format/JsonParser.hx line 145
 └╴ Called from /usr/local/share/haxe/std/haxe/format/JsonParser.hx line 90
    [3 ommited]
CALL Std.int
 └╴ Called from /usr/local/share/haxe/std/haxe/format/JsonParser.hx line 145
 └╴ Called from /usr/local/share/haxe/std/haxe/format/JsonParser.hx line 90
    [3 ommited]
CALL Std.string
 └╴ Called from /usr/local/share/haxe/std/haxe/Log.hx line 34
 └╴ Called from /usr/local/share/haxe/std/haxe/Log.hx line 63
    [2 ommited]
CallStacks.hx:24: { value => 33.3 }

Advanced instrumentation

More complex or specific instrumentation can be achieved by directly calling the instrumenter with a custom transformation function.

uinstrument.Instrument.hijack(<transform>, <class name>, ?<field name>)

Notes

  1. Inline functions are normally ignored; if, however, they are explicitly instrumented (as opposed to being inside a class that's being instrumented), they will loose their AInline access modifier.