ThreadPool

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.

class ThreadPool (

Args...

) {

alias JobD = void delegate(Args);

this(size_t workers, size_t q_size);

void assign(JobD job, Args args);

bool tryAssign(JobD job, Args args);

void append(JobD job, Args args);

size_t pendingJobs();

size_t activeJobs();

void wait();

void shutdown();

void finish();

}

Constructors

this this(size_t workers, size_t q_size): Create a new ThreadPool.

Members

Aliases

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

Functions

activeJobs size_t activeJobs(): Get the number of jobs being executed
append void append(JobD job, Args args): Put a job into the pool for eventual execution.
assign void assign(JobD job, Args args): Assign the given job to a thread immediately or block until one is available
finish void finish(): Complete all pending jobs and shutdown.
pendingJobs size_t pendingJobs(): Get the number of jobs waiting to be executed
shutdown void shutdown(): Finish currently executing jobs and drop all pending.
tryAssign 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)
wait void wait(): Block until all pending jobs complete, but do not shut down. This allows more tasks to be added later.

Examples

// 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.