Hi,
I'm trying to investigate an out-of-memory issue in a WebWorker that uses a
Emscripten compiled JS library.
For this, I would like to profile the memory usage / track memory
allocations.
I checked out the memory profiler from:
https://groups.google.com/forum/#!topic/emscripten-discuss/HtAzVposlX4.
It tries to hook into _malloc and _free by using a preRun callback.
However, this doesn't work anymore. Here is what it tries to do:
*Webworker script*
importScripts("memoryprofiler-webworker.js");
//...import Emscripten library through AMD loader...
*memoryprofiler-webworker.js*
//see https://groups.google.com/forum/#!topic/emscripten-discuss/HtAzVposlX4
function memoryprofiler_add_hooks(){
var prevMalloc = _malloc;
//wrap prevMalloc in hookedMalloc
_malloc = hookedMalloc;
Module['_malloc'] = hookedMalloc;
//same with _free
}
*EmscriptenLibrary.js*
Module['preRun'] = [memoryprofiler_add_hooks];
The problem is that _malloc and _free are not in scope when entering the
memoryprofiler_add_hooks function.
I've tried to pass the Module and asm objects to the
memoryprofiler_add_hooks function:
*EmscriptenLibrary.js*
Module['preRun'] = [];
//...
//later on in the file, after asm object has been constructed (but before
the call to run()):
Module['preRun'].push({func: memoryprofiler_add_hooks, arg: {Module: Module,
asm: asm}});
*memoryprofiler-webworker.js*
function memoryprofiler_add_hooks(args) {
var prevMalloc = args.asm._malloc;
function hookedMalloc(size) {
//.. track memory statistics etc. and delegate to prevMalloc
}
args.asm['_malloc'] = hookedMalloc;
args.Module['_malloc'] = hookedMalloc;
//same with free
}
This works as expected when you call asm._malloc or Module._malloc (or
EmscriptenLibrary._malloc from the webworker). It is hookedMalloc that gets
called instead of the asm _malloc. However, because compiled ASM code
refers to _malloc from inside of the asm object, the original asm._malloc
is still used by compiled ASM code.
*EmscriptenLibrary.js*
// EMSCRIPTEN_START_ASM
var asm = (function(global, env, buffer) {
...
function _malloc($bytes) {
...
}
function compiled_library_function(){
...
_malloc(...); //calls original _malloc, not hookedMalloc, no statistics
are tracked
...
}
}
My question is: Is there any way to hook _malloc or _free? Can I do it from
an external JS with minimal modifications to Emscripten's output? Is it
possible by other means (e.g. linking a JS library)? An Emscripten memory
profiler would be great for developing Emscripten-based JS libraries.
Kind regards,
Glenn
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