How to monitor js_runtime or js_context healthness and gracefully shutdown after specified timeout

[laishere]

Scene:
I want to run a js script in a runtime. The js code may be malformed. For example, infinite loop may happens in normal functions or Promise jobs.

I want to specify a timeout to shutdown context or runtime. When the context or runtime can't make any response after a timeout.
I want to know what's the best way to do this.

I have some thoughts in my mind:

1. Use alarm signal: when the alarm is reached, do something to stop stack machine. Do we have this kind of approch to stop stack machine without droping performance like inserting a byte code or altering the PC to a particular location?
2. Stop the runtime worker thread immediately when monitor thread detects it can't make any response. Which means that the runtime may stop at any instruction point. Can we make sure that we free all the resource after this?

[chqrlie]

Interesting ideas. Will investigate.

[saghul]

I think you might be able to accomplish that with an interrupt handler. You could mark the start of a script with something like clock_gettime, then set an interrupt handler with JS_SetInterruptHandler and every time it hits get a new time mark and if the time is over tear down the engine.

[laishere]

@chqrlie @saghul Thank you for reply. @saghul I think you are right. Just checked the these codes in stack machine evaluation.

https://github.com/bellard/quickjs/blob/36911f0d3ab1a4c190a4d5cbe7c2db225a455389/quickjs.c#L17239-L17243

It checks interrupts before handling goto opcode.

[laishere]

In this way, I guess I can gracefully stop the function call with an uncaught exception from interrupt. I am wondering what will happen inside a promise? The promise never complete?

[saghul]

Yeah it will just be destroyed when the engine is.

[laishere]

Now that I can stop the function call with an exception. I may not shutdown the runtime. What will happen to the uncaught error? I check the interrupt code. It throws an error that can't be caught. JS_CallInternal return the uncaught exception directly. Does that means the uncaught exception will be returned to JS_Eval and JS_ExecutePendingJob?

[saghul]

I think so yeah. Note you could decide to reset the exception by doing JS_GetException or reset the uncatchable flag with JS_ResetUncatchableError so it can be caught...

[laishere]

Thank you! Will look into it. I think I have all the information I want. I will close this issue now.