Fibers for concurrency in PHP - Mini Project: Build & Apply

Fibers for concurrency

📖 Scenario: You are building a simple PHP script that uses fibers to run two tasks concurrently. Fibers allow you to pause and resume code execution, which helps manage multiple tasks without waiting for each to finish before starting the next.

🎯 Goal: Create two fibers that each count numbers with a pause, then run them concurrently by switching between them. Finally, print the combined output showing the interleaved counting.

📋 What You'll Learn

Create two fibers named fiber1 and fiber2 that each count from 1 to 3 with a pause between counts.

Create a variable output to store the combined counting results as a string.

Use a loop to switch between fiber1 and fiber2 until both finish.

Print the output string showing the interleaved counts.

💡 Why This Matters

🌍 Real World

Fibers help PHP programs handle multiple tasks at once without waiting for each to finish, useful in web servers or background jobs.

💼 Career

Understanding fibers prepares you for writing efficient, concurrent PHP code in modern applications and frameworks.

1

Create two fibers for counting

Create two fibers called fiber1 and fiber2. Each fiber should count from 1 to 3. Inside each fiber, use a for loop with variable i from 1 to 3, and after each count, use Fiber::suspend() to pause the fiber.

PHP

<?php

// Create fiber1 and fiber2 that count from 1 to 3 with suspend
// Your code here

Hint

Use new Fiber(function() { ... }) to create each fiber. Inside, use a for loop and call Fiber::suspend() with a string showing the fiber name and count.

2

Create an output variable

Create a variable called output and set it to an empty string "". This will store the combined results from both fibers.

PHP

<?php

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

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

// Create output variable
// Your code here

Hint

Just write $output = ""; to start with an empty string.

3

Run fibers concurrently and collect output

Use a while loop that runs as long as either fiber1 or fiber2 is not terminated. Inside the loop, check if fiber1 is not terminated, then resume it and append the returned string to output. Do the same for fiber2. Use $fiber1->isTerminated() and $fiber2->isTerminated() to check if fibers finished.

PHP

<?php

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

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

$output = "";

// Use a while loop to resume fibers and add their output
// Your code here

Hint

Use while with the condition checking both fibers. Inside, resume each fiber if not terminated and add the returned string to output.

4

Print the combined output

Write a print statement to display the output variable.

PHP

<?php

// Print the output variable
// Your code here

Hint

Use print($output); to show the combined counting results.

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