# pthread_setcancelstate

## NAME



           pthread_setcancelstate, pthread_setcanceltype - set cancelability
           state and type
    


## LIBRARY



           POSIX threads library (_libpthread_ , _-lpthread_)
    


## SYNOPSIS



           **#include <pthread.h>**
    
           **int pthread_setcancelstate(int** _state_**, int ***_oldstate_**);**
           **int pthread_setcanceltype(int** _type_**, int ***_oldtype_**);**
    


## DESCRIPTION



           The **pthread_setcancelstate**() sets the cancelability state of the
           calling thread to the value given in _state_.  The previous
           cancelability state of the thread is returned in the buffer
           pointed to by _oldstate_.  The _state_ argument must have one of the
           following values:
    
           **PTHREAD_CANCEL_ENABLE**
                  The thread is cancelable.  This is the default
                  cancelability state in all new threads, including the
                  initial thread.  The thread's cancelability type determines
                  when a cancelable thread will respond to a cancelation
                  request.
    
           **PTHREAD_CANCEL_DISABLE**
                  The thread is not cancelable.  If a cancelation request is
                  received, it is blocked until cancelability is enabled.
    
           The **pthread_setcanceltype**() sets the cancelability type of the
           calling thread to the value given in _type_.  The previous
           cancelability type of the thread is returned in the buffer pointed
           to by _oldtype_.  The _type_ argument must have one of the following
           values:
    
           **PTHREAD_CANCEL_DEFERRED**
                  A cancelation request is deferred until the thread next
                  calls a function that is a cancelation point (see
                  pthreads(7)).  This is the default cancelability type in
                  all new threads, including the initial thread.
    
                  Even with deferred cancelation, a cancelation point in an
                  asynchronous signal handler may still be acted upon and the
                  effect is as if it was an asynchronous cancelation.
    
           **PTHREAD_CANCEL_ASYNCHRONOUS**
                  The thread can be canceled at any time.  (Typically, it
                  will be canceled immediately upon receiving a cancelation
                  request, but the system doesn't guarantee this.)
    
           The set-and-get operation performed by each of these functions is
           atomic with respect to other threads in the process calling the
           same function.
    


## RETURN VALUE



           On success, these functions return 0; on error, they return a
           nonzero error number.
    


## ERRORS



           The **pthread_setcancelstate**() can fail with the following error:
    
           **EINVAL** Invalid value for _state_.
    
           The **pthread_setcanceltype**() can fail with the following error:
    
           **EINVAL** Invalid value for _type_.
    


## ATTRIBUTES



           For an explanation of the terms used in this section, see
           attributes(7).
           ┌────────────────────────────────┬─────────────────────┬─────────┐
           │ **Interface** │ **Attribute** │ **Value** │
           ├────────────────────────────────┼─────────────────────┼─────────┤
           │ **pthread_setcancelstate**(),      │ Thread safety       │ MT-Safe │
           │ **pthread_setcanceltype**()        │                     │         │
           ├────────────────────────────────┼─────────────────────┼─────────┤
           │ **pthread_setcancelstate**(),      │ Async-cancel safety │ AC-Safe │
           │ **pthread_setcanceltype**()        │                     │         │
           └────────────────────────────────┴─────────────────────┴─────────┘
    


## STANDARDS



           POSIX.1-2008.
    


## NOTES



           For details of what happens when a thread is canceled, see
           pthread_cancel(3).
    
           Briefly disabling cancelability is useful if a thread performs
           some critical action that must not be interrupted by a cancelation
           request.  Beware of disabling cancelability for long periods, or
           around operations that may block for long periods, since that will
           render the thread unresponsive to cancelation requests.
    
       **Asynchronous cancelability**
           Setting the cancelability type to **PTHREAD_CANCEL_ASYNCHRONOUS** is
           rarely useful.  Since the thread could be canceled at _any_ time, it
           cannot safely reserve resources (e.g., allocating memory with
           malloc(3)), acquire mutexes, semaphores, or locks, and so on.
           Reserving resources is unsafe because the application has no way
           of knowing what the state of these resources is when the thread is
           canceled; that is, did cancelation occur before the resources were
           reserved, while they were reserved, or after they were released?
           Furthermore, some internal data structures (e.g., the linked list
           of free blocks managed by the malloc(3) family of functions) may
           be left in an inconsistent state if cancelation occurs in the
           middle of the function call.  Consequently, clean-up handlers
           cease to be useful.
    
           Functions that can be safely asynchronously canceled are called
           _async-cancel-safe functions_.  POSIX.1-2001 and POSIX.1-2008
           require only that pthread_cancel(3), **pthread_setcancelstate**(), and
           **pthread_setcanceltype**() be async-cancel-safe.  In general, other
           library functions can't be safely called from an asynchronously
           cancelable thread.
    
           One of the few circumstances in which asynchronous cancelability
           is useful is for cancelation of a thread that is in a pure
           compute-bound loop.
    
       **Portability notes**
           The Linux threading implementations permit the _oldstate_ argument
           of **pthread_setcancelstate**() to be NULL, in which case the
           information about the previous cancelability state is not returned
           to the caller.  Many other implementations also permit a NULL
           _oldstat_ argument, but POSIX.1 does not specify this point, so
           portable applications should always specify a non-NULL value in
           _oldstate_.  A precisely analogous set of statements applies for the
           _oldtype_ argument of **pthread_setcanceltype**().
    


## EXAMPLES



           See pthread_cancel(3).
    


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