Fiber Not Started Error

Why This Happens

PHP 8.1 Fibers must follow a specific lifecycle: create, start, and then resume only when suspended. Calling resume() on a Fiber that has not been started yet, is already running, or has completed throws this error.

The Problem

$fiber = new Fiber(function (): void {
    echo 'Hello';
    Fiber::suspend();
    echo 'World';
});
$fiber->resume(); // Error: fiber not started

The Fix

$fiber = new Fiber(function (): void {
    echo 'Hello';
    Fiber::suspend();
    echo 'World';
});
$fiber->start();  // Runs until suspend
$fiber->resume(); // Resumes from suspend

Step-by-Step Fix

1. 1

   Check the Fiber state

   Use $fiber->isStarted(), $fiber->isSuspended(), and $fiber->isTerminated() to check the Fiber's current state before operating on it.

2. 2

   Call start() first

   A new Fiber must be started with start() before it can be resumed. Only call resume() after the Fiber has suspended itself.

3. 3

   Handle Fiber completion

   Check isTerminated() before resuming to avoid trying to resume a Fiber that has already finished execution.