---
name: "pthread_join"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/pthread_join"
---

# pthread\_join(3)

join with a terminated thread

## NAME

pthread\_join - join with a terminated thread

## LIBRARY

POSIX threads library (*libpthread*, *-lpthread*)

## SYNOPSIS

```
#include <pthread.h>
```

**int pthread\_join(pthread\_t** *thread***, void \*\****retval***);**

## DESCRIPTION

The **pthread\_join**() function waits for the thread specified by *thread* to terminate. If that thread has already terminated, then **pthread\_join**() returns immediately. The thread specified by *thread* must be joinable.

If *retval* is not NULL, then **pthread\_join**() copies the exit status of the target thread (i.e., the value that the target thread supplied to [**pthread\_exit**(3)](/pthread_exit/3.md)) into the location pointed to by *retval*. If the target thread was canceled, then **PTHREAD\_CANCELED** is placed in the location pointed to by *retval*.

If multiple threads simultaneously try to join with the same thread, the results are undefined. If the thread calling **pthread\_join**() is canceled, then the target thread will remain joinable (i.e., it will not be detached).

## RETURN VALUE

On success, **pthread\_join**() returns 0; on error, it returns an error number.

## ERRORS

- **EDEADLK**

  A deadlock was detected (e.g., two threads tried to join with each other); or *thread* specifies the calling thread.

- **EINVAL**

  *thread* is not a joinable thread.

- **EINVAL**

  Another thread is already waiting to join with this thread.

- **ESRCH**

  No thread with the ID *thread* could be found.

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **pthread\_join**() | Thread safety | MT-Safe |

## STANDARDS

POSIX.1-2008.

## HISTORY

POSIX.1-2001.

## NOTES

After a successful call to **pthread\_join**(), the caller is guaranteed that the target thread has terminated. The caller may then choose to do any clean-up that is required after termination of the thread (e.g., freeing memory or other resources that were allocated to the target thread).

Joining with a thread that has previously been joined results in undefined behavior.

Failure to join with a thread that is joinable (i.e., one that is not detached), produces a "zombie thread". Avoid doing this, since each zombie thread consumes some system resources, and when enough zombie threads have accumulated, it will no longer be possible to create new threads (or processes).

There is no pthreads analog of *waitpid(-1, &status, 0)*, that is, "join with any terminated thread". If you believe you need this functionality, you probably need to rethink your application design.

All of the threads in a process are peers: any thread can join with any other thread in the process.

## EXAMPLES

See [**pthread\_create**(3)](/pthread_create/3.md).

## SEE ALSO

[**pthread\_cancel**(3)](/pthread_cancel/3.md), [**pthread\_create**(3)](/pthread_create/3.md), [**pthread\_detach**(3)](/pthread_detach/3.md), [**pthread\_exit**(3)](/pthread_exit/3.md), [**pthread\_tryjoin\_np**(3)](/pthread_tryjoin_np/3.md), [**pthreads**(7)](/pthreads/7.md)