Fibers for concurrency in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple Fiber switch

What is the output of this PHP code using Fibers?

PHP

<?php
$fiber = new Fiber(function(): void {
    echo "Inside fiber.\n";
    Fiber::suspend();
    echo "Resumed fiber.\n";
});

echo "Before fiber start.\n";
$fiber->start();
echo "Between fiber suspend and resume.\n";
$fiber->resume();
echo "After fiber resume.\n";

A

Inside fiber.
Before fiber start.
Between fiber suspend and resume.
Resumed fiber.
After fiber resume.

B

Before fiber start.
Inside fiber.
Resumed fiber.
Between fiber suspend and resume.
After fiber resume.

C

Before fiber start.
Between fiber suspend and resume.
Inside fiber.
Resumed fiber.
After fiber resume.

D

Before fiber start.
Inside fiber.
Between fiber suspend and resume.
Resumed fiber.
After fiber resume.

💡 Hint

Remember that Fiber::suspend pauses execution inside the fiber and returns control to the caller.

The fiber starts and prints "Inside fiber." then suspends. Control returns to main which prints "Between fiber suspend and resume.". Then resume continues fiber printing "Resumed fiber." and finally main prints "After fiber resume.".

🧠 Conceptual

intermediate

Fiber state after suspension

After a Fiber suspends using Fiber::suspend(), what is the state of the Fiber object?

A The Fiber is terminated and cannot be resumed.

B The Fiber is in 'suspended' state and can be resumed later.

C The Fiber is in 'started' state but cannot be resumed again.

D The Fiber is in 'new' state waiting to start.

💡 Hint

Think about what Fiber::suspend() does to the fiber's execution.

Fiber::suspend() pauses the fiber and puts it in a suspended state. It can be resumed later with Fiber::resume().

🔧 Debug

advanced

Identify the error in Fiber usage

What error will this PHP code produce when run?

PHP

<?php
$fiber = new Fiber(function(): void {
    echo "Running fiber.\n";
});

$fiber->start();
$fiber->resume();

A SyntaxError: Unexpected token 'resume'

B Fatal error: Call to undefined method Fiber::resume()

C FiberError: Cannot resume a terminated fiber

D No error, prints 'Running fiber.' twice

💡 Hint

Consider what happens when you resume a fiber that already finished.

After start(), the fiber runs and terminates. The second resume tries to resume a terminated fiber, causing a FiberError.

🚀 Application

advanced

Using Fibers to simulate cooperative multitasking

Given two fibers that print numbers with suspend calls, what is the output of this code?

PHP

<?php
$fiber1 = new Fiber(function() {
    for ($i = 1; $i <= 3; $i++) {
        echo "Fiber1: $i\n";
        Fiber::suspend();
    }
});

$fiber2 = new Fiber(function() {
    for ($i = 1; $i <= 3; $i++) {
        echo "Fiber2: $i\n";
        Fiber::suspend();
    }
});

$fiber1->start();
$fiber2->start();
$fiber1->resume();
$fiber2->resume();
$fiber1->resume();
$fiber2->resume();

A

Fiber1: 1
Fiber2: 1
Fiber1: 2
Fiber2: 2
Fiber1: 3
Fiber2: 3

B

Fiber2: 1
Fiber1: 1
Fiber2: 2
Fiber1: 2
Fiber2: 3
Fiber1: 3

C

Fiber1: 1
Fiber1: 2
Fiber1: 3
Fiber2: 1
Fiber2: 2
Fiber2: 3

D

Fiber1: 1
Fiber2: 1
Fiber2: 2
Fiber1: 2
Fiber1: 3
Fiber2: 3

💡 Hint

Fibers suspend after each print, so control switches between them.

Each fiber prints a number then suspends. The main code resumes them alternately, so output interleaves numbers from fiber1 and fiber2.

❓ Predict Output

expert

Fiber with return value and exception handling

What is the output of this PHP code using Fibers with return and exception?

PHP

<?php
$fiber = new Fiber(function(): int {
    echo "Start fiber\n";
    Fiber::suspend();
    echo "After suspend\n";
    throw new Exception("Error inside fiber");
    return 42;
});

try {
    $fiber->start();
    echo "Resuming fiber\n";
    $fiber->resume();
} catch (Exception $e) {
    echo "Caught exception: " . $e->getMessage() . "\n";
}

echo "Fiber is terminated: " . ($fiber->isTerminated() ? 'yes' : 'no') . "\n";

A

Start fiber
Resuming fiber
After suspend
Caught exception: Error inside fiber
Fiber is terminated: yes

B

Start fiber
After suspend
Resuming fiber
Caught exception: Error inside fiber
Fiber is terminated: yes

C

Start fiber
Resuming fiber
Caught exception: Error inside fiber
Fiber is terminated: no

D

Start fiber
Resuming fiber
After suspend
Fiber is terminated: yes

💡 Hint

Exception inside fiber is caught outside; fiber terminates after exception.

The fiber starts and prints "Start fiber" then suspends. Main resumes fiber, which prints "After suspend" then throws exception caught outside. Fiber is terminated after exception.