PTHREAD_SETSPECIFIC(3) | Library Functions Manual | PTHREAD_SETSPECIFIC(3)

# NAME

`pthread_setspecific` — set a thread-specific data value

# SYNOPSIS

POSIX Threads Library (libpthread, -lpthread)
`#include <pthread.h>`

int
`pthread_setspecific`(pthread_key_t key, const void *value);

# DESCRIPTION

The `pthread_setspecific`() function associates a thread-specific value with a key obtained via a previous call to `pthread_key_create`(). Different threads may bind different values to the same key. These values are typically pointers to blocks of dynamically allocated memory that have been reserved for use by the calling thread.

The effect of calling `pthread_setspecific`() with a key value not obtained from `pthread_key_create`() or after key has been deleted with `pthread_key_delete`() is undefined.

`pthread_setspecific`() may be called from a thread-specific data destructor function; however, this may result in lost storage or infinite loops.

# RETURN VALUES

If successful, the `pthread_setspecific`() function will return zero. Otherwise an error number will be returned to indicate the error.

# ERRORS

`pthread_setspecific`() will fail if:

[`ENOMEM`]
  Insufficient memory exists to associate the value with the key.
[`EINVAL`]
  The key value is invalid.

# SEE ALSO

pthread_getspecific(3), pthread_key_create(3), pthread_key_delete(3)

# STANDARDS

`pthread_setspecific`() conforms to ISO/IEC 9945-1:1996 (“POSIX.1”).

June 7, 2025 | Debian