tango.core.ThreadPool

This module provides an implementation of the classical thread-pool model.

License:
BSD style:

Author:
Anders Halager

class ThreadPool(Args...);
A thread pool is a way to process multiple jobs in parallel without creating a new thread for each job. This way the overhead of creating a thread is only paid once, and not once for each job and you can limit the maximum number of threads active at any one point.

In this case a "job" is simply a delegate and some parameters the delegate will be called with after having been added to the thread pool's queue.

Example:
// create a new pool with two threads
auto pool = new ThreadPool!(int)(2);
void delegate(int) f = (int x) { Log(x); };

// Now we have three ways of telling the pool to execute our jobs
// First we can say we just want it done at some later point
pool.append(f, 1);
// Secondly we can ask for a job to be done as soon as possible, blocking
// until it is started by some thread
pool.assign(f, 2);
// Finally we can say we either want it done immediately or not at all
if (pool.tryAssign(f, 3))
    Log("Someone took the job!");
else
    Log("No one was available to do the job right now");
// After giving the pool some jobs to do, we need to give it a chance to
// finish, so we can do one of two things.
// Choice no. 1 is to finish what has already been assigned to the threads,
// but ignore any remaining queued jobs
//   pool.shutdown();
// The other choice is to finish all jobs currently executing or in queue:
pool.finish();


If append isn't called there should be no additional heap allocations after initialization.

alias JobD = void delegate(Args);
An alias for the type of delegates this thread pool considers a job

this(size_t workers, size_t q_size = 0);
Create a new ThreadPool.

Params:
size_t workers The amount of threads to spawn
size_t q_size The expected size of the queue (how many elements are preallocated)

void assign(JobD job, Args args);
Assign the given job to a thread immediately or block until one is available

bool tryAssign(JobD job, Args args);
Assign the given job to a thread immediately or return false if none is available. (Returns true if one was available)

void append(JobD job, Args args);
Put a job into the pool for eventual execution.

Warning:
Acts as a stack, not a queue as you would expect

size_t pendingJobs();
Get the number of jobs waiting to be executed

size_t activeJobs();
Get the number of jobs being executed

void wait();
Block until all pending jobs complete, but do not shut down. This allows more tasks to be added later.

void shutdown();
Finish currently executing jobs and drop all pending.

void finish();
Complete all pending jobs and shutdown.


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