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. To use this you construct an instance of the work queue manager, then divide the work
up into units that can be processed independently and queue each unit of work, and finally
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
returned by the Sync() method (formerly WaitForComplete()) or the WaitOne()
or the Wait().
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 requests worker jobs from this category's pool attach to the work group you are
creating, if there are not enough worker jobs in the pool and the pool is not at the 'MaxActiveWorkers' limit
then the framework will start additional workers automatically. The number of worker jobs we start is determined by
the work queue manager based on current machine load and characteristics of the CPU the machine is running on.
Every work group is guaranteed at least one worker process to be assigned as soon as a unit of work is queued. Additional
workers requested for this group will be allocated from the worker pool if there are workers not already processing work
units from other groups. These additional workers are allocated on a first come first serve basis.
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.
Call Queue() to queue a unit of work to be run, this takes either a class method
call, or a '$$func^rtn' reference and then any arguments you need to pass to this function. We support passing arrays
here using the standard '.array' syntax although changes in the array by the work unit are not returned to the caller.
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 must 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 the work
unit will run inside 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 call Sync() 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.
Instead of waiting for all work units to complete with the Sync() you can obtain notification of each completion
using the WaitOne() interface which is an iterator over the work completion events. Another mechanism to run code
when each work unit is completed is the QueueCallback() method.
Work units may write to the public variable %result which will be relayed to the parent process in either the
WaitOne() call or in the callback function from the QueueCallback().
Worker jobs are owned by the parent process while they are performing work in this group, so when the parent exits
the worker jobs will be released immediately. When the object returned by %New is destroyed this will remove all work associated
with this group automatically, and release any workers.
The work queued should not perform exclusive kills or argumentless unlocks as this will interfere with the framework.
Use of process private globals are only helpful within a chunk of work and not across chunks as different chunks of work are processed
by different workers in different jobs.
The size of each chunk should be on the order of thousands of lines of ObjectScript 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 as these jobs are shared among all work entered
into the work queue manager in the same 'category'.
The third argument to %New() is the category which specifies which work queue pool to allocate
worker jobs from. These categories are independent of each other so for example 'SQL' work is allocated from a different
pool to 'Default' work and the load placed on the system from each of the categories can be tuned.
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 parent 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 parent process.
Return the number of worker jobs that we will request for this group. We request workers as units of work
are queued, the first worker is requested when the first unit of work is queued. Once we have requested
this number of workers we will not request any more. Note that after a worker is requested it may not be
cause any worker to attach to this queue if they are all busy doing other work.
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 queue, but leaves the work itself so you can call Resume() at a later point.
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 non-null timeout it will wait
for up to this timeout value in seconds for work currently in progress to finish.
If after the timeout the work
in progress has exited it will set completed=1 else this will be 0.
Queues a specific unit of work, you pass the entry point to call in 'work' argument. This can be either '##class(Classname).ClassMethod'
or '$$entry^rtn' and it is expected to return a %Status code on completion. To call a function
that does not return any value on completion then prepend the class syntax with '=' e.g. '=##class(Classname).ClassMethod'
or to call a function do not include the '$$' e.g. '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 parent 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 recorded when this function is called and is used when the work is executed.
Output the work unit makes to the current device will be trapped and relayed to the parent process after this work unit
has complted and when the parent process is waiting for work to be completed. If a work unit wishes to flush output before
the work unit has completed then then call 'Do $system.WorkMgr.Flush()'
Similar to Queue() except you can also pass in a 'callback' which is a function or class method that
is called in the parent process when this unit of work is complete. This function is called with the same arguments
the original 'work' is called with so it can tell 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. Any error returned by the work unit will by default be added to the Sync()
return %Status, but the callback may alter the the work units %Status by modifying the public variable '%status'. For example
if the callback detects a specific error %Status from the work unit and does a 'Set %status=$$$OK' it will mark
this error as handled and no error %Status will be added to the return from Sync().
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.
