Ruby Multithreading

Multithreading is a powerful feature in Ruby that allows a program to perform multiple tasks concurrently. However, multithreading also adds complexity to your program and can lead to issues such as race conditions if not handled properly.

Here's a basic tutorial on how to use threads in Ruby:

1. Creating a Thread:

You can create a new thread in Ruby using the Thread.new method:

thread = Thread.new do
  5.times do |i|
    puts "Thread is at #{i}"
    sleep 1
  end
end

thread.join  # Wait for the thread to finish

In this example, a new thread is created that runs a loop 5 times, each time outputting a message and then sleeping for 1 second.

2. Joining Threads:

The join method is used to make the main program wait for the thread to finish before it continues. If you don't call join, the main program may finish before the thread has a chance to run.

3. Multiple Threads:

You can create multiple threads and run them concurrently:

threads = []

5.times do |i|
  threads << Thread.new do
    puts "Thread #{i} is starting"
    sleep 1
    puts "Thread #{i} is ending"
  end
end

threads.each { |thread| thread.join }

In this example, 5 threads are created. Each thread outputs a start message, sleeps for 1 second, and then outputs an end message. The main program waits for all the threads to finish before it continues.

4. Thread Safety:

When multiple threads access shared data, there's a risk of race conditions, where the threads interfere with each other. Ruby provides several mechanisms to handle this, such as Mutexes:

counter = 0
mutex = Mutex.new

threads = 10.times.map do
  Thread.new do
    mutex.synchronize do
      temp = counter
      temp = temp + 1
      counter = temp
    end
  end
end

threads.each(&:join)
puts counter  # Outputs: 10

In this example, a Mutex is used to ensure that only one thread at a time can access the counter variable, preventing race conditions.

Note: Be aware that due to the Global Interpreter Lock (GIL) in MRI Ruby (the standard version of Ruby), true parallel execution of threads isn't possible - although they will still be concurrent, and you'll still have to watch out for issues like race conditions. Other implementations of Ruby, such as JRuby or Rubinius, do allow parallel execution of threads.

Thread class in Ruby: The Thread class in Ruby is used for creating and managing threads.

thread = Thread.new do
  puts "This is a thread"
end
thread.join  # Wait for the thread to finish

Creating threads in Ruby: Threads can be created using the Thread.new constructor.
```
thread = Thread.new do
  puts "This is a thread"
end
```

Synchronization in Ruby threads: Synchronization is important to prevent race conditions and ensure thread safety.

counter = 0
mutex = Mutex.new

thread1 = Thread.new do
  mutex.synchronize do
    counter += 1
  end
end

thread2 = Thread.new do
  mutex.synchronize do
    counter += 1
  end
end

thread1.join
thread2.join

Mutex in Ruby multithreading: The Mutex class is used for achieving mutual exclusion in multithreading.

mutex = Mutex.new

thread1 = Thread.new do
  mutex.synchronize do
    # Critical section
  end
end

Thread safety in Ruby: Thread safety ensures that shared data is accessed in a way that avoids conflicts and race conditions.
```
# Use synchronization mechanisms like Mutex to achieve thread safety
```

Ruby thread variables: Thread variables allow data to be shared between threads.

thread = Thread.new do
  Thread.current[:data] = "Shared data"
end

thread.join
puts thread[:data]

Ruby global variables in multithreading: Global variables are shared among all threads, so caution is needed to ensure thread safety.
```
$global_variable = 42
```

Thread pooling in Ruby: Thread pooling involves creating a pool of reusable threads to handle tasks.

require 'thread'

pool = Queue.new
5.times { |i| pool << Thread.new { puts "Thread #{i}" } }
pool.size.times { pool.pop.join }

Handling exceptions in Ruby threads: Exception handling is crucial in multithreaded environments to avoid unexpected termination.

thread = Thread.new do
  begin
    # Code that might raise an exception
  rescue => e
    puts "Exception: #{e.message}"
  end
end