[Vm-dev] Re: fun with callbackEnter

[Andreas Raab]

Oh. Interesting observation. Sounds right to me. Guess we'll have to add 
a checkForInterrupts() to callbackEnter. BTW, this strongly resonates 
with what I was writing about the event driven VM. In that scheme 
"callbackEnter" would be a straightforward call to interpret().

Cheers,
   - Andreas

John M McIntosh wrote:
> Since we are talking about events, this is an error thrown by a iphone 
> squeak vm setup as a single pthread.
> 
> What happens is ioGetNextEvent is called which calls ioProcessEvents 
> which on a special version of the iphone vm
> calls [NSRunLoop currentRunLoop] to run for N milliseconds.
> 
> When the run loop runs it ends up sending a message to an Objective-C 
> SqueakProxy instance which then signals
> a squeak semaphore to wake up the VM. In this specialized VM it does
> 
>         interpreterProxy->signalSemaphoreWithIndex(sem);
>         interpreterProxy->callbackEnter(&callbackid);
> 
> However I *think* the problem here is that although we signal the 
> semaphore then issue the forceInterruptCheck
> in callbackEnter: this does not actually alter the runnable processes 
> list since that work is only done when
> checkForInterrrupts() is run.  Thus in this case the only process 
> running is the idleProcess, and it's sleeping
> but we are attempting to wake a squeakProxy process waiting on the 
> semaphore we did signal, but
> as you see oops nada runnable, so die.
> 
> 
> 
> 2009-11-10 12:59:36.214 x[13886:207] forwardInvocation: <NSInvocation: 
> 0x1368370>
> 2009-11-10 12:59:36.215 x[13886:207] currentThread: <NSThread: 
> 0x1105e90>{name = (null), num = 1}
> 2009-11-10 12:59:36.219 x[13886:207] inside lock 0
> 2009-11-10 12:59:36.220 x[13886:207] signalling squeak
> 
> scheduler could not find a runnable process
> 
> 548435824 >idleProcess
> 548435732 >startUp
> 548291060 BlockClosure>newProcess
> 
> 
> 
> callbackEnter: callbackID
>     "Re-enter the interpreter for executing a callback"
>     | result activeProc |
>     self export: true.
>     self var: #callbackID declareC: 'sqInt *callbackID'.
> 
>     "For now, do not allow a callback unless we're in a primitiveResponse"
>     primitiveIndex = 0 ifTrue:[^false].
> 
>     "Check if we've exceeded the callback depth"
>     jmpDepth >= jmpMax ifTrue:[^false].
>     jmpDepth := jmpDepth + 1.
> 
>     "Suspend the currently active process"
>     activeProc := self fetchPointer: ActiveProcessIndex
>                          ofObject: self schedulerPointer.
>     suspendedCallbacks at: jmpDepth put: activeProc.
>     "We need to preserve newMethod explicitly since it is not activated yet
>     and therefore no context has been created for it. If the caller 
> primitive
>     for any reason decides to fail we need to make sure we execute the 
> correct
>     method and not the one 'last used' in the call back"
>     suspendedMethods at: jmpDepth put: newMethod.
>     self transferTo: self wakeHighestPriority.
> 
>     "Typically, invoking the callback means that some semaphore has been
>     signaled to indicate the callback. Force an interrupt check right 
> away."
>     self forceInterruptCheck.
> 
>     result := self setjmp: (jmpBuf at: jmpDepth).
>     result == 0 ifTrue:["Fill in callbackID"
>         callbackID at: 0 put: jmpDepth.
>         "This is ugly but the inliner treats interpret() in very special 
> and strange ways and calling any kind of 'self interpret' either 
> directly or even via cCode:inSmalltalk: will cause this entire method to 
> vanish."
>         self cCode: 'interpret()'.
>     ].
> 
>     "Transfer back to the previous process so that caller can push result"
>     activeProc := self fetchPointer: ActiveProcessIndex
>                          ofObject: self schedulerPointer.
>     self putToSleep: activeProc.
>     activeProc := suspendedCallbacks at: jmpDepth.
>     newMethod := suspendedMethods at: jmpDepth.    "see comment above"
>     self transferTo: activeProc.
>     jmpDepth := jmpDepth-1.
>     ^true
> 
> 
> 
> -- 
> ===========================================================================
> John M. McIntosh <johnmci at smalltalkconsulting.com>   Twitter:  
> squeaker68882
> Corporate Smalltalk Consulting Ltd.  http://www.smalltalkconsulting.com
> ===========================================================================
> 
> 
> 
>