ROOT   Reference Guide
RooFit::MultiProcess::Job Class Referenceabstract

interface class for defining the actual work that must be done

Think of "job" as in "employment", e.g. the job of a baker, which involves tasks like baking and selling bread. The Job must define the tasks through its execution (evaluate_task), based on a task index argument.

Classes inheriting from Job must implement the pure virtual methods:

An example/reference implementation can be found in test_Job.cxx.

Most Jobs will also want to override the virtual update_state() function. This function can be used to send and receive state from master to worker. In the worker loop, when something is received over the ZeroMQ "SUB" socket, update_state() is called to put the received data into the right places, thus updating for instance parameter values on the worker that were updated since the last call on the master side.

## Message protocol

One simple rule must be upheld for the messages that the implementer will send with 'send_back_task_result_from_worker' and 'update_state': the first part of the message must always be the 'Job''s ID, stored in 'Job::id'. The rest of the message, i.e. the actual data to be sent, is completely up to the implementation. Note that on the receiving end, i.e. in the implementation of 'receive_task_result_on_master', one will get the whole message, but the 'Job' ID part will already have been identified in the 'JobManager', so one needn't worry about it further inside 'Job::receive_task_result_on_master' (it is already routed to the correct 'Job'). The same goes for the receiving end of 'update_state', except that update_state is routed from the 'worker_loop', not the 'JobManager'.

A second rule applies to 'update_state' messages: the second part must be a state identifier. This identifier will also be sent along with tasks to the queue. When a worker then takes a task from the queue, it can check whether it has already updated its state to what is expected to be there for the task at hand. If not, it should wait for the new state to arrive over the state subscription socket. Note: it is the implementer's task to actually update 'Job::state_id_' inside 'Job::update_state()'!

## Implementers notes

The type of result from each task is strongly dependent on the Job at hand and so Job does not provide a default results member. It is up to the inheriting class to implement this in the above functions. We would have liked a template parameter task_result_t, so that we could also provide a default "boilerplate" calculate function to show a typical Job use-case of all the above infrastructure. This is not trivial, because the JobManager has to keep a list of Job pointers, so if there would be different template instantiations of Jobs, this would complicate this list.

A typical Job implementation will have an evaluation function that is called from the master process, like RooAbsArg::getVal calls evaluate(). This function will have three purposes: 1. send updated parameter values to the workers (possibly through update_state() or in a dedicated function), 2. queue tasks and 3. wait for the results to be retrieved. 'Job::gather_worker_results()' is provided for convenience to wait for all tasks to be retrieved for the current Job. Implementers can also choose to have the master process perform other tasks in between any of these three steps, or even skip steps completely.

Child classes should refrain from direct access to the JobManager instance (through JobManager::instance), but rather use the here provided Job::get_manager(). This function starts the worker_loop on the worker when first called, meaning that the workers will not be running before they are needed.

Definition at line 25 of file Job.h.

## Public Member Functions

Job ()

Job (const Job &other)

~Job ()

void gather_worker_results ()
Wait for all tasks to be retrieved for the current Job. More...

std::size_t get_state_id ()
Get the current state identifier. More...

virtual void update_state ()
Virtual function to update any necessary state on workers. More...

## Protected Member Functions

JobManagerget_manager ()
Get JobManager instance; create and activate if necessary. More...

## Protected Attributes

std::size_t id_

std::size_t state_id_ = 0

## Private Attributes

JobManager_manager = nullptr

#include </home/sftnight/build/workspace/root-makedoc-master/rootspi/rdoc/src/master/roofit/multiprocess/res/RooFit/MultiProcess/Job.h>

Inheritance diagram for RooFit::MultiProcess::Job:
[legend]

## ◆ Job() [1/2]

 RooFit::MultiProcess::Job::Job ( )
explicit

Definition at line 93 of file Job.cxx.

## ◆ Job() [2/2]

 RooFit::MultiProcess::Job::Job ( const Job & other )

Definition at line 98 of file Job.cxx.

## ◆ ~Job()

 RooFit::MultiProcess::Job::~Job ( )

Definition at line 103 of file Job.cxx.

pure virtual

## ◆ gather_worker_results()

 void RooFit::MultiProcess::Job::gather_worker_results ( )

Wait for all tasks to be retrieved for the current Job.

Definition at line 130 of file Job.cxx.

## ◆ get_manager()

 JobManager * RooFit::MultiProcess::Job::get_manager ( )
protected

Get JobManager instance; create and activate if necessary.

Child classes should refrain from direct access to the JobManager instance (through JobManager::instance), but rather use the here provided Job::get_manager(). This function starts the worker_loop on the worker when first called, meaning that the workers will not be running before they are needed.

Definition at line 116 of file Job.cxx.

## ◆ get_state_id()

 std::size_t RooFit::MultiProcess::Job::get_state_id ( )

Get the current state identifier.

Definition at line 145 of file Job.cxx.

pure virtual

pure virtual

## ◆ update_state()

 void RooFit::MultiProcess::Job::update_state ( )
virtual

Virtual function to update any necessary state on workers.

This function is called from the worker loop when something is received over the ZeroMQ "SUB" socket. The master process sends messages to workers on its "PUB" socket. Thus, we can update, for instance, parameter values on the worker that were updated since the last call on the master side.

Note
Implementers: make sure to also update the state_id_ member.

Definition at line 142 of file Job.cxx.

## ◆ _manager

 JobManager* RooFit::MultiProcess::Job::_manager = nullptr
private

Definition at line 50 of file Job.h.

## ◆ id_

 std::size_t RooFit::MultiProcess::Job::id_
protected

Definition at line 45 of file Job.h.

## ◆ state_id_

 std::size_t RooFit::MultiProcess::Job::state_id_ = 0
protected

Definition at line 46 of file Job.h.

The documentation for this class was generated from the following files:
• roofit/multiprocess/res/RooFit/MultiProcess/Job.h
• roofit/multiprocess/src/Job.cxx