Thread creation and execution in Ruby - Step-by-Step Execution

Concept Flow - Thread creation and execution

Start main program

↓

Create new thread

↓

Thread starts running block

↓

Thread executes code

↓

Thread finishes

↓

Main program continues or waits

↓

Program ends

The main program creates a thread that runs code concurrently. The thread executes its block and finishes, while the main program can continue or wait.

Execution Sample

Ruby

thread = Thread.new do
  puts "Hello from thread"
end
thread.join
puts "Main program ends"

This code creates a thread that prints a message, waits for it to finish, then prints a final message.

Execution Table

Step	Action	Thread State	Output	Main Program State
1	Main program starts	No thread yet		Running
2	Create new thread with block	New thread created		Running
3	Thread starts running block	Running	Hello from thread	Running
4	Thread finishes block	Finished	Hello from thread	Waiting at join
5	Main program resumes after join	Finished	Hello from thread	Running
6	Main program prints final message	Finished	Hello from thread Main program ends	Running
7	Program ends	Finished	Hello from thread Main program ends	Exited

💡 Thread finishes execution and main program ends after printing all messages.

Variable Tracker

Variable	Start	After Step 2	After Step 4	Final
thread	nil	Thread object created	Thread finished	Thread finished

Key Moments - 2 Insights

Why does the main program wait at thread.join?

Because thread.join pauses the main program until the thread finishes, as shown in execution_table step 4.

What happens if we don't call thread.join?

The main program may finish before the thread runs or completes, so the thread's output might not appear, unlike step 4 where join waits.

Visual Quiz - 3 Questions

Look at the execution table, what is the thread state at step 3?

A New thread created

B Finished

C Running

D No thread yet

💡 Hint

Check the 'Thread State' column at step 3 in the execution_table.

At which step does the main program wait for the thread to finish?

A Step 4

B Step 3

C Step 2

D Step 6

💡 Hint

Look at the 'Main Program State' column to find when it is 'Waiting at join'.

If we remove thread.join, what will likely happen to the output?

A Both messages print in order

B Only 'Main program ends' prints

C Only 'Hello from thread' prints

D No output prints

💡 Hint

Without join, main program may finish before thread runs, so only main message prints.

Concept Snapshot

Thread creation in Ruby:
thread = Thread.new { code }
Thread runs code concurrently.
Use thread.join to wait for thread to finish.
Without join, main may finish first.
Threads allow parallel tasks.

Full Transcript

This example shows how Ruby creates and runs a thread. The main program starts and creates a new thread with Thread.new. The thread runs the code block, printing 'Hello from thread'. The main program calls thread.join to wait until the thread finishes. After the thread ends, the main program prints 'Main program ends' and then exits. Variables like 'thread' hold the thread object, which changes state from created to finished. Key points include understanding that join pauses the main program until the thread completes, and without join, the main program might finish before the thread runs. The execution table tracks each step, thread state, output, and main program state to visualize the flow.