Subj : Re: Stopping scripte execution [JS_SetBranchCallback users, please
To   : Jun Kim
From : Brendan Eich
Date : Thu Dec 02 2004 06:36 pm

Jun Kim wrote:
> Oh, and perhaps, with a example code?
> Thank you~~ :)


Several examples can be found via 
http://lxr.mozilla.org/mozilla/search?string=JS_SetBranchCallback.

Of course you need to set the branch callback *before* executing scripts 
whose backward branches and returns you wish to monitor.

This reminds me: I'm thinking, and patching in 
https://bugzilla.mozilla.org/show_bug.cgi?id=272880, of extended the 
branch callback so that native loops and other costly native code 
structures invoke it with a null |script| (2nd) parameter.  This would 
help catch runaway or nearly-runaway cases such as the much-duplicated 
bug testcase in https://bugzilla.mozilla.org/show_bug.cgi?id=271716.

This is not a compatible API change, since until now, the branch 
callback has always been invoked with a non-null script parameter.  So 
the backward compatible way to make this change is to condition the new 
calls from native code on a JSOPTION_NATIVE_BRANCH_CALLBACK (or shorter 
named) option.

The best way to use the branch callback will always be to avoid doing 
anything (return as soon as possible) most of the time, but every 2^n 
calls (which can be cheaply tested with an unsigned counter masked 
against a constant), check that too much time hasn't passed since the 
script started.  That implies the counter is zeroed at start of script 
execution.

Hope this helps,

/be

.