Fibers for concurrency in PHP

Introduction

Fibers let you pause and resume parts of your program. This helps run multiple tasks smoothly without waiting for each to finish.

When you want to run several tasks that wait for something, like reading files or network calls.

When you want to keep your program responsive while doing slow work.

When you want to write code that looks simple but runs tasks one after another without blocking.

When you want to manage multiple small jobs inside one program without using heavy threads.

Syntax

PHP

<?php
$fiber = new Fiber(function(): void {
    // code to run inside the fiber
    $value = Fiber::suspend('pause');
    echo "Resumed with value: $value\n";
});

// Start the fiber
$result = $fiber->start();
echo "Fiber suspended with: $result\n";

// Resume the fiber
$fiber->resume('hello');

Create a Fiber with new Fiber(function() { ... }).

Use Fiber::suspend() to pause and send a value outside.

Examples

Simple fiber that just prints a message.

PHP

<?php
$fiber = new Fiber(function() {
    echo "Inside fiber\n";
});
$fiber->start();

Fiber suspends and sends 'waiting', then resumes with 'done'.

PHP

<?php
$fiber = new Fiber(function() {
    $value = Fiber::suspend('waiting');
    echo "Got: $value\n";
});

$result = $fiber->start();
echo "Suspended with: $result\n";
$fiber->resume('done');

Sample Program

This program shows how a fiber pauses and resumes multiple times, exchanging data with the main program.

PHP

<?php
$fiber = new Fiber(function(): void {
    echo "Step 1: Start\n";
    $value = Fiber::suspend('paused at step 1');
    echo "Step 2: Resumed with $value\n";
    $value = Fiber::suspend('paused at step 2');
    echo "Step 3: Resumed with $value\n";
});

// Start fiber and get first suspend value
$suspendValue = $fiber->start();
echo "Main received: $suspendValue\n";

// Resume fiber with a value
$suspendValue = $fiber->resume('data for step 2');
echo "Main received: $suspendValue\n";

// Resume fiber again
$fiber->resume('data for step 3');

Important Notes

Fibers are not threads; they run in the same thread but can pause and resume.

Use fibers to write asynchronous code in a simple, step-by-step style.

Summary

Fibers let you pause and resume code blocks to handle tasks smoothly.

You create fibers with new Fiber() and control them with start() and resume().

Fibers help keep programs responsive without complex threading.

Practice

1. What is the main purpose of using Fiber in PHP?

easy

A. To speed up database queries automatically

B. To create permanent background threads

C. To pause and resume code execution for concurrency

D. To replace all loops with asynchronous calls

Solution

1. Step 1: Understand Fiber's role

   Fibers allow pausing and resuming code blocks, enabling concurrency without threads.

2. Step 2: Compare options

   Only To pause and resume code execution for concurrency correctly describes Fibers' purpose; others describe unrelated features.

3. Final Answer:

   To pause and resume code execution for concurrency -> Option C

4. Quick Check:

   Fibers = pause and resume concurrency [OK]

Hint: Fibers let you pause and resume code easily [OK]

Common Mistakes:

• Thinking Fibers create real threads
• Assuming Fibers speed up database automatically
• Confusing Fibers with async loops

2. Which of the following is the correct way to start a Fiber in PHP?

easy

A. $fiber->run();

B. $fiber->execute();

C. $fiber->begin();

D. $fiber->start();

Solution

1. Step 1: Recall Fiber methods

   The Fiber class uses start() to begin execution.

2. Step 2: Check other options

   Methods like run(), begin(), and execute() do not exist for Fiber.

3. Final Answer:

   $fiber->start(); -> Option D

4. Quick Check:

   Fiber starts with start() method [OK]

Hint: Use start() to begin Fiber execution [OK]

Common Mistakes:

• Using run() instead of start()
• Trying to call execute() or begin()
• Confusing Fiber methods with thread methods

3. What will be the output of this PHP code using Fiber?

$fiber = new Fiber(function(): void {
    $value = Fiber::suspend('paused');
    echo "Resumed with: $value";
});

echo $fiber->start();
$fiber->resume('data');

medium

A. pausedResumed with: data

B. Resumed with: datapaused

C. paused

D. Resumed with: data

Solution

1. Step 1: Analyze Fiber start()

   The start() runs until Fiber::suspend('paused'), which returns 'paused'. So, echo outputs 'paused'.

2. Step 2: Analyze Fiber resume()

   The resume('data') continues after suspend, echoing "Resumed with: data".

3. Final Answer:

   pausedResumed with: data -> Option A

4. Quick Check:

   start() returns suspend value, resume() continues [OK]

Hint: start() returns suspend value, resume() continues execution [OK]

Common Mistakes:

• Assuming start() returns void
• Thinking resume() returns suspend value
• Mixing order of output strings

4. Identify the error in this Fiber code snippet:

$fiber = new Fiber(function() {
    echo "Start\n";
    Fiber::suspend();
    echo "End\n";
});

$fiber->resume();

medium

A. Fiber::suspend() cannot be called without a value

B. Fiber must be started with start(), not resume() first

C. Fiber constructor requires a return type declaration

D. Fiber cannot echo strings inside its function

Solution

1. Step 1: Check Fiber start method usage

   Fibers must be started with start() before calling resume().

2. Step 2: Validate other options

   Calling Fiber::suspend() without value is allowed; no return type needed; echo is valid inside Fiber.

3. Final Answer:

   Fiber must be started with start(), not resume() first -> Option B

4. Quick Check:

   start() first, then resume() [OK]

Hint: Always start Fiber with start() before resume() [OK]

Common Mistakes:

• Calling resume() before start()
• Thinking suspend() needs a value
• Expecting Fiber function to require return type

5. You want to run two Fibers concurrently to simulate two tasks. Which approach correctly switches between them to print alternating messages?

$fiber1 = new Fiber(function() {
    for ($i = 0; $i < 3; $i++) {
        echo "A$i ";
        Fiber::suspend();
    }
});

$fiber2 = new Fiber(function() {
    for ($i = 0; $i < 3; $i++) {
        echo "B$i ";
        Fiber::suspend();
    }
});

// Which code below correctly alternates execution?

A) {
    $fiber1->start();
    $fiber2->start();
    $fiber1->resume();
    $fiber2->resume();
}

B) {
    $fiber1->start();
    $fiber1->resume();
    $fiber2->start();
    $fiber2->resume();
}

C) {
    $fiber1->start();
    $fiber2->start();
    $fiber2->resume();
    $fiber1->resume();
}

D) {
    $fiber1->start();
    $fiber2->start();
    $fiber1->resume();
    $fiber1->resume();
}

hard

A. Start both fibers, then alternate resume calls: fiber1->resume(), fiber2->resume()

B. Start and resume fiber1 twice before starting fiber2

C. Start both fibers, then resume fiber2 before fiber1

D. Start both fibers, then resume fiber1 twice without resuming fiber2

Solution

1. Step 1: Understand Fiber suspension

   Each Fiber suspends after printing one message, so to alternate, we must resume them in turn.

2. Step 2: Analyze options for alternating resumes

   Start both fibers, then alternate resume calls: fiber1->resume(), fiber2->resume() starts both fibers, then resumes fiber1 and fiber2 alternately, producing alternating output. Others resume one fiber multiple times or in wrong order.

3. Final Answer:

   Start both fibers, then alternate resume calls: fiber1->resume(), fiber2->resume() -> Option A

4. Quick Check:

   Alternate resume calls for concurrency [OK]

Hint: Alternate resume calls to switch between fibers [OK]

Common Mistakes:

• Resuming one fiber multiple times before the other
• Starting fibers but not resuming correctly
• Resuming fibers in wrong order