2009/5/5 Andreas Raab <andreas.raab at gmx.de>:
> Just for fun, find an attached a version of MultiWait that works just like
> described earlier. If you run the benchmarks on MultiWait you'll find that
> DelayWaitTimeout is about 5x faster when compared with the naive MultiWait
> equivalent.
>
Obviously, this is because in #waitForOne you have to create a
separate forks for each event , for waiting on them.
This is because currently, a waiter can be only the Process.
In contrast, in new implementation we could allow a waiter to be any
object - and in case of MultiWait this will be 'self'.. i.e.

MultiWait>>waitForOne
	"Waits for signals from at least one event source.
	Returns all semaphores that have been signaled."
	| waitSema processes |

       signaled := Array new: eventSemas size. "signaled is an ivar,
and actually can be initialized once we setting eventSemas collection
"
        eventSemas do: [:sema |
            sema waitForSignalBy: self. "let receiver wait for signal
from semaphore"
        ].
       self wait.
	^signaled

> Cheers,
>  - Andreas
>
> Andreas Raab wrote:
>>
>> Hi Igor -
>>
>> How is what you are proposing fundamentally different from a solution that
>> simply creates a watcher process for each event source and then combines
>> those properly? I.e.,
>>
>> Object subclass: #MultiWait
>>  instanceVariableNames: 'eventSemas'
>>  ...
>>
>> waitForAll
>>  "waits for signals from all event sources"
>>  eventSemas do:[:sema| sema wait].
>>
>> waitForOne
>>  "Waits for signals from at least one event source.
>>   Returns all the semaphores that have been signaled."
>>  waitSema := Semaphore new.
>>  processes := eventSemas do:[:sema| [sema wait. waitSema signal] fork].
>>  waitSema wait. "or waitTimeoutMSecs:"
>>  signaled := Set new.
>>  eventSemas with: processes do:[:list :proc|
>>    (proc suspend == list) ifTrue:[signaled add: list].
>>    proc terminate.
>>  ].
>>  ^signaled
>>
>> DelayWaitTimeout is an optimization that avoids the need for additional
>> processes - when you use #waitTimeoutMSecs: a *lot* (say, because you're
>> running a server with heavy network activity) the additional overhead
>> incurred by the additional processes (and process switches) gets relevant in
>> a hurry. But other than that, the above is a straightforward solution that
>> will work with anything that supports the #wait protocol.
>>
>> Cheers,
>>  - Andreas
>>
>> Igor Stasenko wrote:
>>>
>>> Hello list,
>>>
>>> I stared @ DelayWaitTimeout class, and thinking, how to implement it
>>> in new scheduler..
>>> First i thought , just make it quickly and forget about it, but one
>>> thing which don't makes me feel good about it, that
>>> DelayWaitTimeout is a perfect example, when you need to stop a Process
>>> until one of the multiple events occurs - in case of DelayWaitTimeout
>>> its either semaphore signaled or delay expired.
>>>
>>> So, i thinking, what if instead of implementing a DelayWaitTimeout ,
>>> which works only for 2 objects - delay & semaphore, implement a more
>>> generic class , which would allow us to wait for any number of objects
>>> and blocks process until one of them is signaled. Or, blocks process
>>> until all of them signaled.
>>> There's nothing new, in fact, in Windoze there an API function, called
>>> WaitForMultipleObjects, which does exactly what i describing - it
>>> could wait on multiple objects, releasing a waiter once a single
>>> object signaled, or release waiter only after all objects signaled.
>>>
>>> Here is my thoughts, how to implement that.
>>> First, we need to allow Delay & Semaphore to work with abstract waiter
>>> object (not just Process).
>>> A proposed protocol between object which acts as one who can be waited
>>> on, and object who acts as waiter is following:
>>>
>>> To start waiting, we sending a #waitForSignalBy: waiter
>>> semaphore waitForSignalBy: waiter
>>> or
>>> delay waitForSignalBy: waiter
>>>
>>> then, default #wait could be implemented, in both cases, simply as:
>>>
>>> ^ self waitForSignalBy: Processor activeProcess.
>>>
>>> now, after issuing #waitForSignalBy: we have the following possible
>>> cases:
>>> - given object is already signaled (as a semaphore with excess
>>> signals), in this case we immediately sending #waitComplete: to waiter
>>>
>>> - given object is scheduled for being signaled later , in this case we
>>> sending #startWaitingOn: to waiter.
>>>
>>> - now after #startWaitingOn: issued and once a semaphore/delay
>>> signaled we sending #waitComplete: to waiter.
>>>
>>> - in case if semaphore/delay abandoned, we sending #waitAbandoned: to
>>> waiter. This happens, for instance, when we terminating a process who
>>> currently waits on semaphore.
>>>
>>> (If you have a better idea how to name these messages, please make a
>>> guess)
>>>
>>> Now, by having such protocol implemented for Delay, Semaphore &
>>> Process, we now can easily introduce another class which could allow
>>> us to wait for multiple events.
>>>
>>> Again, i'm not sure how properly call it..
>>> Just want to illustrate the usage:
>>>
>>> semaphore := Semaphore new.
>>> delay := Delay forMilliseconds: 100.
>>>
>>> signaler := (MultipleWait on: { semaphore. delay }) waitForOne.  "wait
>>> until one of the listed objects get signaled"
>>> or:
>>> result := (MultipleWait on: { semaphore. delay }) waitForAll. "wait
>>> until all of the listed objects get signaled"
>>>
>>> by default, MultipleWait>>waitForSignalBy: is releasing waiter once
>>> one of the listed objects signaled (as in waitForOne case).
>>> Not sure about return result of #waitForAll, IMO , it could be just a
>>> boolean value - return true, if all objects signaled, or false in case
>>> if waiting abandoned.
>>>
>>> Now, of course, since  MultipleWait acts as a waiter and as an object
>>> who can be waited on, we can allow nesting:
>>>
>>> mwait1 := MultipleWait on: { sema1. sema2 }.
>>> (MultipleWait on: { mwait1. delay }) waitForOne.
>>>
>>> and finally, as you may guess , a Semaphore>>waitTimeoutMSecs: now can
>>> be implemented as:
>>>
>>> waitTimeoutMSecs: anInteger
>>>    "Wait on this semaphore for up to the given number of milliseconds,
>>> then timeout.
>>>    Return true if the deadline expired, false otherwise."
>>>    | delay |
>>>
>>>       delay := Delay forMilliseconds: (anInteger max: 0).
>>>       ^ delay == (MultipleWait on: { self. delay }) waitForOne.
>>>
>>>
>>
>>
>>
>
>
>
>
>



-- 
Best regards,
Igor Stasenko AKA sig.