Fibers allow the creation of full-stack, uninterruptible functions that can be used to implement cooperative multitasking in PHP. These are also known as coroutines or green-threads.
Fibers pause the entire execution stack, so the direct caller of the function does not need to change how it invokes the function.
Execution may be interrupted anywhere in the call stack using Fiber::suspend() (that is, the call to Fiber::suspend() may be in a deeply nested function or not even exist at all).
Unlike stack-less Generators, each Fiber has its own call stack, allowing them to be paused within deeply nested function calls. A function declaring an interruption point (i.e., calling Fiber::suspend()) need not change its return type, unlike a function using yield which must return a Generator instance.
Fibers can be suspended in any function call, including those called from within the PHP VM, such as functions provided to array_map or methods called by foreach on an Iterator object.
Once suspended, execution of the fiber may be resumed with any value using Fiber->resume() or by throwing an exception into the fiber using Fiber->throw(). The value is returned (or exception thrown) from Fiber::suspend().
$fiber = new Fiber(function (): void {
$value = Fiber::suspend('fiber');
echo "Value used to resume fiber: ", $value, "\n";
});
$value = $fiber->start();
echo "Value from fiber suspending: ", $value, "\n";
$fiber->resume('test');
//output:
Value from fiber suspending: fiber
Value used to resume fiber: test
