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    The parallel\Future class

    (0.8.0)

    Futures

    A Future represents the return value or uncaught exception from a task, and exposes an API for cancellation.

    Example #1 Example showing Future as return value

    <?php
    $runtime     = new \parallel\Runtime;
    $future = $runtime->run(function(){
    return     "World";
    });
    printf("Hello %s\n", $future->value());
    ?>

    Il precedente esempio visualizzerà qualcosa simile a:

    Hello World

    The behaviour of a future also allows it to be used as a simple synchronization point even where the task does not return a value explicitly.

    Example #2 Example showing Future as synchronization point

    <?php
    $runtime     = new \parallel\Runtime;
    $future = $runtime->run(function(){
    echo     "in child ";
    for (    $i = 0; $i < 500; $i++) {
    if (    $i % 10 == 0) {
    echo     ".";
    }
    }
    echo     " leaving child";
    });

    $future->value();
    echo     "\nparent continues\n";
    ?>

    Il precedente esempio visualizzerà qualcosa simile a:

    in child .................................................. leaving child
parent continues

    Sommario della classe

    final class parallel\Future {
    /* Resolution */
    public value(): mixed
    /* State */
    public cancelled(): bool
    public done(): bool
    /* Cancellation */
    public cancel(): bool
    }

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    Thierry Kauffmann
    3 years ago
    <?php

    /**
    * Sample parallel Runtime/Future processing
    * using a generator to produce the list of items to process
    *
    * Items to process in parallel come from a generator
    * It could be anything : e.g fetch a mysql array, a DirectoryIterator...
    * Thus the number of items to process in parallel is NOT known in advance
    *
    * This algorithm attributes items to each parallel thread dynamically
    * As soon as a thread has finished working
    * It is assigned a new item to process
    * until all items are processed (generator closes)
    *
    * In this example we process 50 items in 5 parallel threads
    * It produces output in this form (output changes at each run) :
    *
    * ThreadId: 1 => Item: 1 (Start)
    * ThreadId: 2 => Item: 2 (Start)
    * ThreadId: 3 => Item: 3 (Start)
    * ThreadId: 4 => Item: 4 (Start)
    * ThreadId: 5 => Item: 5 (Start)
    * ThreadId: 5 => Item: 5 Sleep: 3s (End)
    * ThreadId: 5 => Item: 6 (Start)
    * ThreadId: 3 => Item: 3 Sleep: 4s (End)
    * ThreadId: 3 => Item: 7 (Start)
    * ThreadId: 2 => Item: 2 Sleep: 6s (End)
    * ThreadId: 2 => Item: 8 (Start)
    * ...
    * ThreadId: 4 => Item: 44 Sleep: 6s (End)
    * ThreadId: 4 => Item: 49 (Start)
    * ThreadId: 3 => Item: 46 Sleep: 5s (End)
    * ThreadId: 3 => Item: 50 (Start)
    * ThreadId: 2 => Item: 43 Sleep: 9s (End)
    * Destroy ThreadId: 2
    * ThreadId: 1 => Item: 47 Sleep: 5s (End)
    * Destroy ThreadId: 1
    * ThreadId: 4 => Item: 49 Sleep: 7s (End)
    * Destroy ThreadId: 4
    * ThreadId: 5 => Item: 48 Sleep: 10s (End)
    * Destroy ThreadId: 5
    * ThreadId: 3 => Item: 50 Sleep: 10s (End)
    * Destroy ThreadId: 3
    */

    // Generate list of items to process with a generator
    function generator(int $item_count) {
    echo     "Item count: $item_count\n";
    for (    $i=1; $i <= $item_count; $i++) {
    yield     $i;
    }
    }

    function     testConcurrency(int $concurrency, int $max_item_count) {

    // Set item_count to a random number so that each run is different
    $item_count= rand(1, $max_item_count);
    // Create generator
    $generator = generator($item_count);

    // Function executing in each thread. Have a snap for a random time for example !
    // You could make some calculation here or transfer files or whatever...
    $producer = function (int $item_id) {
    $seconds = rand(1, 10);
    sleep($seconds);
    return [    'item_id' => $item_id, 'sleep_seconds' => $seconds];
    };

    // Fill up threads with a single future initialized to 'false' value
    for ($thread_id = 1; $thread_id <= $concurrency; $thread_id++) {
    $threads[$thread_id] = ['runtime' => new \parallel\Runtime(), 'future' => false];
    }

    // Create infinite loop for the whole processing
    while (true) {
    // Loop through threads until generator closes and all threads are destroyed
    foreach ($threads as $thread_id => &$thread) {
    if (    $thread['future'] === false and $generator->valid()) {
    // Thread is inactive and generator still has values : run something in the thread
    $item_id = $generator->current();
    $thread['future'] = $thread['runtime']->run($producer, [$item_id]);
    echo     "ThreadId: $thread_id => Item: $item_id (Start)\n";
    $generator->next();
    } elseif (    $thread['future'] === false) {
    // Destroy thread in case generator is closed
    echo "Destroy ThreadId: $thread_id\n";
    unset(    $threads[$thread_id]);
    } elseif (    $thread['future']->done()) {
    // Thread finished working. Get result value.
    $item = $thread['future']->value();
    echo     "ThreadId: $thread_id => Item: {$item['item_id']} Sleep: {$item['sleep_seconds']}s (End)\n";
    // Thread is ready to run again
    $thread['future'] = false;
    }
    }

    // Escape infinite loop when all threads are destroyed
    if (empty($threads)) break;
    }
    }

    $concurrency = 5;
    $item_count = 50;

    testConcurrency($concurrency, $item_count);

    ?>
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