photon

Photon is a lightweight transparent fiber scheduler. It's inspired by Golang's green thread model and the spawn function is called go doing the same job that Golang's keyword does. The framework API surface is kept to a minimum, many programs can be written using only three primitives: startloop to initialize Photon, runFibers to start fiber scheduler and go to create tasks, including the initial tasks.

Discussion

Example, showcasing channels and std.range interop: 

  1. module examples.channels;

import std.algorithm, std.datetime, std.range, std.stdio;
import photon;

void first(shared Channel!string work, shared Channel!int completion) {
    delay(2.msecs);
    work.put("first #1");
    delay(2.msecs);
    work.put("first #2");
    delay(2.msecs);
    work.put("first #3");
    completion.put(1);
}

void second(shared Channel!string work, shared Channel!int completion) {
    delay(3.msecs);
    work.put("second #1");
    delay(3.msecs);
    work.put("second #2");
    completion.put(2);
}

void main() {
    startloop();
    auto jobQueue = channel!string(2);
    auto finishQueue = channel!int(1);
    go({
        first(jobQueue, finishQueue);
    });
    go({ // producer # 2
        second(jobQueue, finishQueue);
    });
    go({ // consumer
        foreach (item; jobQueue) {
            delay(1.seconds);
            writeln(item);
        }
    });
    go({ // closer
        auto completions = finishQueue.take(2).array;
        assert(completions.length == 2);
        jobQueue.close(); // all producers are done
    });
    runFibers();
}

  • Task

    Declaration

    struct Task;

    Task result allows one fiber to wait on the other by joining the execution.

  • startloop

    Declaration

    nothrow @trusted Task startloop();

    Initialize event loop and internal data structures for Photon scheduler.

  • go

    Declaration

    @trusted Task go(void delegate() func);
    @safe Task go(void function() func);

    Setup a fiber task to run on the Photon scheduler.

  • goOnSameThread

    Declaration

    @trusted Task goOnSameThread(void delegate() func);
    @safe Task goOnSameThread(void function() func);

    Same as go but make sure the fiber is scheduled on the same thread of the threadpool. Could be useful if there is a need to propagate TLS variable.

  • offload

    Declaration

    @trusted T offload(T)(T delegate() work);

    Run work on a dedicated thread pool and pass the result back to the calling fiber or thread. This avoids blocking event loop on computationally intensive tasks.

  • runFibers

    Declaration

    @trusted void runFibers();

    Start sheduler and run fibers until all are terminated.

  • mutex

    Declaration

    auto mutex();

    Create non-recursive mutex

    Examples

    1. startloop();
auto mtx = mutex();
int counter = 0;
go({
    foreach (_; 0..100) {
        mtx.lock();
        int c = counter;
        delay(1.msecs);
        counter = c + 1;
        mtx.unlock();
    }
});
go({
    foreach (_; 0..100) {
        mtx.lock();
        int c = counter;
        delay(1.msecs);
        counter = c + 1;
        mtx.unlock();
    }
});
runFibers();
mtx.dispose();
assert(counter == 200);

  • recursiveMutex

    Declaration

    auto recursiveMutex();

    Create recursive mutex

  • Channel

    Declaration

    struct Channel(T);

    A ref-counted channel that is safe to share between multiple fibers. In essence it's a multiple producer single consumer queue, that implements OutputRange and InputRange concepts.

    • put

      Declaration

      void put(T value);

      OutputRange contract - puts a new item into the channel.

    • empty

      Declaration

      bool empty();

      Part of InputRange contract - checks if there is an item in the queue. Returns true if channel is closed and its buffer is exhausted.

    • front

      Declaration

      ref T front();

      Part of InputRange contract - returns an item available in the channel.

    • popFront

      Declaration

      void popFront();

      Part of InputRange contract - advances range forward.

  • channel

    Declaration

    @safe auto channel(T)(size_t capacity = 1);

    Create a new shared Channel with given capacity.

  • select

    Declaration

    @trusted void select(Args...)(auto ref Args args) if (allSatisfy!(isChannel, Even!Args) && allSatisfy!(isHandler, Odd!Args));

    Multiplex between multiple channels, executes a lambda attached to the first channel that becomes ready to read.

  • isChannel

    Declaration

    enum auto isChannel(T);

    Trait for testing if a type is Channel

  • Pool

    Declaration

    class Pool(T);

    Generic pool

    • release

      Declaration

      void release(Pooled!T item);

      Put pooled item to reuse

    • dispose

      Declaration

      void dispose(Pooled!T item);

      call on items that errored or cannot be reused for some reason

  • pool

    Declaration

    @trusted auto pool(T)(size_t size, Duration maxIdle, T delegate() open, void delegate(ref T) close);

    Create generic pool for resources, open creates new resource, close releases the resource.