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;
- 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.