Bug 41072 – Remove the JSLock when JSC_MULTIPLE_THREADS is disabled

• Status: UNCONFIRMED
• Component: JavaScriptCore

[Yi Shen]

For some platform like Symbian, on which the JSC_MULTIPLE_THREADS is disabled, the implementation of JSLock is empty. While the JSLock are used very often in JavaScriptcall, for example, 

void JSEventListener::handleEvent(...) {
    ...
    JSLock lock(SilenceAssertionsOnly);
    ...
}

We can remove this kind of useless JSLock by using macro like following, to improve the performance and battery life for the mobile device (especially for the webkit-based widget which may keep running javascript all the time).

void JSEventListener::handleEvent(...) {
    ...
#if ENABLE(JSC_MULTIPLE_THREADS)
    JSLock lock(SilenceAssertionsOnly);
#endif
    ...
}

[Mark Rowe (bdash)]

If’ing every use of JSLock would be incredibly ugly.  If the implementation of JSLock when JSC_MULTIPLE_THREADS  is not defined is empty and defined inline in a header any decent compiler will completely optimize this code away.  That’s a much cleaner solution than touching every single place that JSlock is used.

[Yi Shen]

Yes, I am totally agree with you Mark. But these empty JSLock functions are not defined inline in header file, right?

[Mark Rowe (bdash)]

So instead of changing to code to inline the functions your proposal is to #if all of the callsites?  Why not just inline the functions?!

[Yi Shen]

Yes, I can change it to inline if you think it is necessary :)

[Laszlo Gombos]

Let's check the assembly generated by RVCT/GCC before we change the source.