[Vm-dev] Where to get Monitor implementation based on primitives?
dionisiydk at gmail.com
Mon Jan 11 13:58:20 UTC 2016
Eliot I found that there are no methods for simulation code (if it right
name for it). So stepping over new primitives failed (which is infinite
recursion for Pharo case)
Context>>doPrimitive: primitiveIndex method: meth receiver: aReceiver args:
(primitiveIndex = 186 or: [primitiveIndex = 187]) ifTrue:
[| active effective |
active := Processor activeProcess.
effective := active effectiveProcess.
"active == effective"
value := primitiveIndex = 186
ifTrue: [aReceiver *primitiveEnterCriticalSectionOnBehalfOf*: effective]
^(self isPrimFailToken: value)
ifFalse: [self push: value]].
How this methods should be implemented?
2016-01-11 13:59 GMT+01:00 Denis Kudriashov <dionisiydk at gmail.com>:
> I publish slice 17373
> I introduce LockOwnership class which implements VM primitives as:
> - acquire
> - tryAcquire
> - release
> (It comment saves copyright from CriticalSection)
> Mutext uses it as ownership instance variable to implement critical
> methods correctly:
> - critical:
> - critical:ifLocked:
> - critical:ifError:
> - critical:ifCurtailed:
> For the integration process old Mutex instance variables are not removed. So
> loading this code should not broke current Mutex instances. But when we
> integrate it Mutex will have only variable ownership.
> If you look critical implementation you will understand why I not like
> semantic of primitives. it should be inverted in future. #acquire should
> return true when ownership is acquired right now.
> Process>>terminate now detects waiting on LockOwnership and ask it to
> handle wait termination.Then LockOwnership inject right value into lock
> state variable. Such variables should be marked with special pragma
> <lockAt: #ownershipVariableName tracksStateAt: 1> "index of local
> Method can contain mulpible pragmas to reference all ownerships in method.
> ReadWriteLock for example needs this.
> 2016-01-11 13:30 GMT+01:00 Henrik Johansen <henrik.s.johansen at veloxit.no>:
>> On 08 Jan 2016, at 4:25 , Ben Coman <btc at openInWorld.com
>> <btc at openinworld.com>> wrote:
>> On Fri, Jan 8, 2016 at 9:39 PM, Ben Coman <btc at openinworld.com> wrote:
>> On Fri, Jan 8, 2016 at 5:42 PM, stephane ducasse
>> <stephane.ducasse at gmail.com> wrote:
>> I have a (stupid) question.
>> Is the code running without the primitives?
>> Are the code below the primitives correct?
>> I asked that because we can have 100 eyes and brains on the smalltalk
>> level and far less on the VM primitive level.
>> 1. Concurrency bugs can be subtle and the *exact* conditions can be
>> hard to reproduce for debugging. For example, the solution to a
>> couple of problems with Delay   were solved by moving away from
>> Semaphore>>critical: to use signalling.
>> 2. The in-image atomicity of determining whether a signal was actually
>> consumed or not during process suspension/termination is awkward. Its
>> seems hard to *really* know for sure it right (but I haven't looked in
>> depth into Denis' latest proposals.)
>> 3. The existing in-image implementation of Semaphore>>critical messes
>> around in Process>>terminate in a *special* way that is not easy for
>> those 100 eyes to understand. For example, I personally am not
>> comfortable with understanding how the special Semaphore handling in
>> Process>>terminate works, but I can easily follow how
>> primitiveEnterCriticalSection just looking at the code .
>> Points 2 & 3 might possibly be addressed by having new
>> *always* return true, so if the process is terminated while waiting,
>> the assignment to signalConsumed doesn't occur...
>> critical: mutuallyExcludedBlock
>> signalConsumed := false.
>> signalConsumed := self primitiveWaitReturned.
>> blockValue := mutuallyExcludedBlock value
>> ] ensure: [ signalConsumed ifTrue: [self signal] ].
>> where primitiveWait (https://git.io/vuDjd) is copied
>> and (just guessing) the marked line added...
>> | sema excessSignals activeProc inInterpreter |
>> sema := self stackTop. "rcvr"
>> "==>>" self pop: argumentCount + 1 thenPush: objectMemory trueObject.
>> excessSignals := self fetchInteger: ExcessSignalsIndex ofObject: sema.
>> excessSignals > 0
>> [self storeInteger: ExcessSignalsIndex
>> ofObject: sema
>> withValue: excessSignals - 1]
>> inInterpreter := instructionPointer >= objectMemory
>> activeProc := self activeProcess.
>> self addLastLink: activeProc toList: sema.
>> self transferTo: self wakeHighestPriority from: CSWait.
>> forProcessPrimitiveReturnToExecutivePostContextSwitch: inInterpreter]
>> which I guess could be added quickly if Esteban could compile the
>> latest pharo-spur-vm ;)
>> cheers -ben
>> Won't work, there's no guarantee thread has actually ran and
>> signalConsumed been assigned the primitive result after Semaphore resumed
>> the waiting thread, before a higher priority thread runs and terminates
>> it. (which is exactly the case handled by special code in #terminate)
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