What is the difference between PHP Fibers and parallel extension in PHP?

PHP Fibers and parallel extension in PHP both aim to provide parallelism in PHP applications, but they achieve this in different ways. PHP Fibers allow for cooperative multitasking within a single thread, enabling developers to write asynchronous code in a synchronous style. On the other hand, the parallel extension in PHP allows for true parallelism by creating separate threads that can run concurrently. The choice between PHP Fibers and the parallel extension depends on the specific requirements of the application and the level of parallelism needed.

// Example code demonstrating the use of PHP Fibers for cooperative multitasking
$fiber = new Fiber(function() {
    echo "Hello, ";
    Fiber::yield();
    echo "world!";
});
$fiber->start();
$fiber->resume();

// Example code demonstrating the use of parallel extension in PHP for true parallelism
$future = parallel\run(function() {
    return "Hello, world!";
});
echo $future->value();