[Javascript] atomic operations

[Scott Reynen]

On May 3, 2006, at 9:00 AM, Andrew Clover wrote:

>> So multiple events, timeouts etc. will all be scheduled for execution
>> one after the other, and they will all be performed in their entirety
>> before the next one will start executing.
>
> This makes perfect sense and *should* be what happens. Except, it  
> isn't always.
>
> From bitter experience I know of two particular cases where it does  
> not:
>
>  - In Firefox 1.5 (at least; probably all Mozilla, possibly other  
> browsers), when you call a browser dialogue function such as  
> window.alert(). At this point other event handlers/timeouts can  
> fire and their code will execute in the middle of the execution of  
> the alert()ing script block.
>
>  - In IE with Java (at least Sun Java 1.4 on IE6, probably all IE 
> +Sun Java; does not affect MS JVM), when you call any method (or  
> access any property) on an applet from JavaScript, other event  
> handlers/timeouts can fire and their code will execute in the  
> middle of the execution of the applet-calling code. This is  
> especially pernicious where multiple threads of script are trying  
> to silently call an applet, as totally random intermittant faults  
> can result.

In both cases, the event is a call to a process outside of  
JavaScript.  Alerts call the browser's window manager and then the  
event is over until the window manager initiates a new event with a  
response.  Applet calls call the applet and then the event is over  
until the applet creates a new event with a response.  So these are  
both actually *two* events, one call and one response, which work  
exactly as David stated above.  The ability to launch external  
threads doesn't make JavaScript multi-threaded.  There's still only  
one thread of *JavaScript events*.

Also, I'd say that's not what *should* happen.  When I set a timeout  
for 10 seconds, it would ideally execute in exactly ten seconds, not  
ten seconds plus whatever time it takes to clear the event queue.

Peace,
Scott