wait/notifyAll like in Java

[Sean Kelly]

Juan Jose Comellas wrote:
> Graham St Jack wrote:
> 
>> Frank Benoit (keinfarbton) wrote:
>>> While porting java stuff, i come to this:
>>>
>>> How can I implement a JObject class as a base of all the ported classes
>>> to have wait/notify/notifyAll with the behaviour like in Java.
> [...]
>> I would prefer to explicitly create condition variables (yes, more than
>> one allowed) in an object, all tied to the object's monitor. The lack of
>> multiple conditions per object is an issue in Java because you need
>> complicated schemes involving child objects whenever you need multiple
>> conditions.
>>
>> Explicit creation of conditions is appropriate because most objects with
>> a monitor don't need conditions.
>>
>> This subject has been coming up on and off for years - can we please get
>> something added to the runtime (if necessary) and to phobos and tango to
>> implement conditions in a standard way? The lack of conditions tied to
>> object monitors is a real pain.
> 
> This functionality is already present in Tango SVN. I have added a function
> called _d_monitorget() to Tango's runtime library in 
> lib/compiler/{dmd,gdc}/monitor.c. This function allows access to an
> Object's monitor. I have also modified the Mutex class in Tango to use its
> own monitor for locking and I have added a MutexProxy class to allow any
> object to have a mutex interface. With these modifications and the ones
> made to the tango.util.locks.Condition module it becomes trivial to have
> multiple condition variables associated to an Object's monitor and to
> implement the wanted Java-like functionality.

For what it's worth, this feature will not be present in the next 
release of Tango so it can be evaluated a bit more carefully.  While I 
like what it does, the way it is implemented would be the first 
requirement of its kind (ie. telling the runtime /how/ something must be 
implemented instead of /what/ must be implemented).  I want to take some 
more time to weigh alternatives before adding this feature to an actual 
release.  The optimal solution may simply be to add wait(), notify(), 
and notifyAll() to Object like in Java.  I haven't had the time to think 
it through yet.


Sean