This class provides an interface to the work queue manager code that allows work to be distributed to multiple
processes in order to improve performance. In order to use this you need to divide the work up into units that
can be processed independently then you initialize the worker jobs, then queue each unit of work and finally you
wait for the work to be completed. The units of work can output to the current device which will be buffered up
and output to the main job's device when that unit of work is signalled as complete. Also all units of work by
default are expected to return a %Status value so it can indicate errors, these are displayed and
returned by the Sync() method (formerly WaitForComplete()).
A typical calling sequence is:
Set queue=$system.WorkMgr.%New("") If queue="" ; Report Error, can check %objlasterror for %Status code
For i=1:1:100 {
Set sc=queue.Queue("##class(MyClass).ClassMethod",i) If $$$ISERR(sc) ; Report Error
}
Set sc=queue.Sync() If $$$ISERR(sc) ; Report Error
The call to create a new WQM instance will allocate some worker jobs from the pool to the work group you are
creating, if there are not enough worker jobs in the pool then a daemon process will start additional worker
automatically. The number of worker jobs we start determined by the work queue manager based on current machine
load and characteristics of the CPU the machine is running on. If numberjobs=0 is passed in on the %New call
we will not use any workers jobs at all and will do all the processing in the current job in the Sync() method (formerly WaitForComplete()) call.
Then you call Queue() to queue a unit of work to be completed, this takes either a class method
call, or a '$$func^rtn' reference and then any arguments you need to pass to this function. As soon as the
first Queue() is called a worker will start processing this item of work. It is important to make
sure that all the units of work are totally independent and they do not rely on other work units. You can not
rely on the order in which the units of work are processed. If the units may be changing a common global you
will need to add locking to ensure one worker can not change a global while another worker is in the middle of
reading this global. When a unit of work is queued the current security context is stored so when the work
is run it will use the current security context. Note that the worker jobs are started by the super server
and so will run as the operating system user that the super server process is setup to use, this may be different
to your current logged in operating system user.
Finally you call Sync()WaitForComplete) to wait for all the units of work to be complete, display any
output each unit produced and report any errors reported from the work units. The Sync()
will use the qualifiers provided in the Initialize().
Worker jobs are owned by the master process while they are performing work in this group, so when the master exits
the worker jobs will be released immediately. When the object returned by Initialize is destroyed this will remove all work associated
with this group automatically, and release any workers.
Note that the work queued should not use exclusive news, kills or unlocks as this will interfere with the framework.
Also if you use process private globals to store data during the processing note that as multiple jobs will
be processing each chunk you can not rely on accessing these from the master process (or even from another chunk).
The size of each chunk should be on the order of thousands of lines of COS code to ensure the overhead of the framework is
not a significant factor, also rather than a few very large chunks (e.g. 4 big chunks) if possible it is better
to have a fairly large number (100 say) of chunks as this allows us to scale with CPU cores. Worker jobs once started
will remain until they time out given a long enough period of inactivity.
classmethod Attach(token, ByRef sc As %Status) as WorkMgr
If you have called Detach() on a work queue and have the associated token you can pass this into this class method
and assuming the work queue still exists it will create an instance of the work queue manager associated this this queue.
If it fails then it will return $$$NULLOREF and set sc with the error %Status value.
classmethod DefaultNumWorkers(category="Default") as %Integer
Return the default number of worker jobs we will use if no specific number is specified
Detach this oref from the work queue and set token which you can use in another process (or in this process if wanted)
to call Attach(). The timeout is how long in seconds we will keep information about this work queue in the
system, so if you do not Attach to this within this period of time we will remove all information about this queue and any
subsequent call to Attach() will fail.
Called from a worker job to flush any output produced so far to the master process.
Without this all output from a worker job is buffered until this unit of work is complete and only
then is it displayed in the master process.
After the Initialize() is called this will return the current number of worker jobs that are active for this group.
If the group is detached it will return -1.
Pause any work in this work queue, this stops any workers from picking up additional items from
this specific queue, but leaves the work itself so you can call Resume().
When no timeout is passed this will return immediately so there could still be work
in progress from one of the work units that was being process at the time this function was called.
If you pass in a none null timeout after removing existing work from the queue it will wait
for up to this timeout value in seconds for work in progress to finish. If after the timeout the work
in progress has exited it will set completed=1 else this will be 0. You can call this method
passing in 0 for the timeout if you want to ask if work in progress has finished without waiting.
Queues a specific unit of work, you pass the entry point to call in 'work' argument. This can be either '##class(Classname).ClassMethod'
or '$$entry^rtn' and it is expected to return a %Status code on completion. If you want to call a function
that does not return any value on completion then prepend the class syntax with '=' such as '=##class(Classname).ClassMethod'
or for calling a function do not include the '$$' for example 'entry^rtn'.
The item being called may also throw exceptions in order to indicate an error happened which is trapped and converted
to a %Status value to be returned in the master process. You can also pass additional
arguments including arrays by reference. Note that the size of the data passed in these arguments should be kept
relatively small, if there is a large amount of information that needs to be passed then put this in a global.
The security context of the caller is also recorded when this function is called so it can be used when the work
is executed.
Similar to Queue() except you can also pass in a 'callback' which is a function or class method that
is called in the master process when this unit of work is complete. This function is called with the same arguments
the original 'work' is called with so it knows which unit of work is complete. Also the callback function can access
the '%job' public variable which is the $job of the process which really did the work, the '%status' public variable
which is the %Status return code from the work unit this is the callback for and '%workqueue' public variable which
is the oref of the work queue instance.
If using the Wait() to wait for the work to be completed the callback can signal that it should
return to the caller rather than waiting for more events by setting the public variable '%exit' to 1.
