start and join

Learn process management with start and join.

What are start and join?

.start() sends a Process to run; .join() waits for it to finish. Together they manage the process lifecycle.

After start the process runs in the background. The main program continues immediately. When join is called the main program waits for the process to finish. The order matters: start first, then join. Without join the main program may exit before the process finishes, causing unexpected behavior.

Multiple processes

You create multiple Process objects, start them all with start, then wait with join. This is the basic pattern of parallel work.

For example if you start two processes and join them in order, both run in parallel and the main program does not continue until both finish. The output order may depend on how fast each process completes; for deterministic results you use Queue. But lifecycle management is always the same: all start calls first, then all join calls.

Exercise Sequential output with start and join

Import with from multiprocessing import Process. Define a worker function that does print("bitti"). Create a process with Process(target=worker). Call .start() and .join(). Then print "tamam" in the main program.

Show example solution

from multiprocessing import Process

def worker():
    print("done")

p = Process(target=worker)
p.start()
p.join()
print("tamam")

Test yourself

Match start/join concepts

start

Launches the process
join

Waits for completion
target

Function
Process

Process object
Complete the join call
```
p.start()
p.____()
```
Show answer
```
p.start()
p.join()
```
What happens without join?
```
from multiprocessing import Process
p = Process(target=func)
p.start()
# no join
print('done')
```
- The main program continues without waiting
- The process never starts
- The process runs forever
- It raises an error
Show answer

The main program continues without waiting — answer: the main program continues without waiting. join provides the wait.

Next lesson: Queue

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