Fibers
Learn to write thread-like coroutines with the Fiber class.
What is a Fiber?
PHP 8.1 added the Fiber class: a coroutine, a thread-like unit of cooperative execution. It is a piece of code that can pause and resume within the same call stack.
Create one with new Fiber(fn). The ->start() method runs it; Fiber::suspend() pauses and returns to the caller; ->resume() continues.
Fibers are not OS threads; they enable cooperative multitasking. No other fiber runs unless the current one pauses.
Data between suspend and resume
Inside a fiber, Fiber::suspend($v) halts execution and returns $v to the start() call. The caller resumes with ->resume($w); $w becomes the result of suspend().
This builds a two-way value flow between the fiber and the caller. When the fiber completes, getReturn() reads its return value.
Typical uses: asynchronous I/O, producer-consumer patterns and event loop implementations.
Exercise A basic Fiber flow
Create a Fiber: when started it should print fiber-start, pause with Fiber::suspend(), then print fiber-end after resume.
Outside, call start(), print main1, call resume(), print main2. Output order should be fiber-start, main1, fiber-end, main2.
Show example solution
$f = new Fiber(function (): void {
echo "fiber-start\n";
Fiber::suspend();
echo "fiber-end\n";
});
$f->start();
echo "main1\n";
$f->resume();
echo "main2\n";Test yourself
-
Which method starts a Fiber?
- run()
- begin()
- start()
- launch()
Show answer
start() — Correct. The start() method of the Fiber class begins the fiber and sends the initial value.
-
Fiber suspend call
$f = new Fiber(function ($n) { echo $n; ____($n + 1); });Show answer
$f = new Fiber(function ($n) { echo $n; Fiber::suspend($n + 1); }); -
Match the Fiber concepts
- Fiber
- coroutine class
- start
- begins the fiber
- suspend
- pauses the fiber
- resume
- continues a paused fiber