[Vm-dev] Where to get Monitor implementation based on primitives?
dionisiydk at gmail.com
Mon Jan 11 14:54:12 UTC 2016
I write it such way:
[owningProcess := activeProcess.
owningProcess = activeProcess ifTrue:
self addLast: Processor activeProcess.
activeProcess suspend] valueUnpreemptively
[owningProcess := activeProcess.
owningProcess = activeProcess ifTrue: [^true].
2016-01-11 14:58 GMT+01:00 Denis Kudriashov <dionisiydk at gmail.com>:
> 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: arguments
> (primitiveIndex = 186 or: [primitiveIndex = 187]) ifTrue:
> [| active effective |
> active := Processor activeProcess.
> effective := active effectiveProcess.
> "active == effective"
> value := primitiveIndex = 186
> ifTrue: [aReceiver *primitiveEnterCriticalSectionOnBehalfOf*: effective]
> ifFalse: [aReceiver
> *primitiveTestAndSetOwnershipOfCriticalSectionOnBehalfOf*: effective].
> ^(self isPrimFailToken: value)
> ifTrue: [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:
>>> 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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