PTHREAD_SETCANCELSTATE(3)  POSIX Programmer's Manual PTHREAD_SETCANCELSTATE(3)



PPRROOLLOOGG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NNAAMMEE
       pthread_setcancelstate, pthread_setcanceltype, pthread_testcancel --
       set cancelability state

SSYYNNOOPPSSIISS
       #include <pthread.h>

       int pthread_setcancelstate(int _s_t_a_t_e, int *_o_l_d_s_t_a_t_e);
       int pthread_setcanceltype(int _t_y_p_e, int *_o_l_d_t_y_p_e);
       void pthread_testcancel(void);

DDEESSCCRRIIPPTTIIOONN
       The _p_t_h_r_e_a_d___s_e_t_c_a_n_c_e_l_s_t_a_t_e() function shall atomically both set the
       calling thread's cancelability state to the indicated _s_t_a_t_e and return
       the previous cancelability state at the location referenced by
       _o_l_d_s_t_a_t_e.  Legal values for _s_t_a_t_e are PTHREAD_CANCEL_ENABLE and
       PTHREAD_CANCEL_DISABLE.

       The _p_t_h_r_e_a_d___s_e_t_c_a_n_c_e_l_t_y_p_e() function shall atomically both set the
       calling thread's cancelability type to the indicated _t_y_p_e and return
       the previous cancelability type at the location referenced by _o_l_d_t_y_p_e.
       Legal values for _t_y_p_e are PTHREAD_CANCEL_DEFERRED and
       PTHREAD_CANCEL_ASYNCHRONOUS.

       The cancelability state and type of any newly created threads,
       including the thread in which _m_a_i_n() was first invoked, shall be
       PTHREAD_CANCEL_ENABLE and PTHREAD_CANCEL_DEFERRED respectively.

       The _p_t_h_r_e_a_d___t_e_s_t_c_a_n_c_e_l() function shall create a cancellation point in
       the calling thread. The _p_t_h_r_e_a_d___t_e_s_t_c_a_n_c_e_l() function shall have no
       effect if cancelability is disabled.

RREETTUURRNN VVAALLUUEE
       If successful, the _p_t_h_r_e_a_d___s_e_t_c_a_n_c_e_l_s_t_a_t_e() and _p_t_h_r_e_a_d___s_e_t_c_a_n_c_e_l_t_y_p_e()
       functions shall return zero; otherwise, an error number shall be
       returned to indicate the error.

EERRRROORRSS
       The _p_t_h_r_e_a_d___s_e_t_c_a_n_c_e_l_s_t_a_t_e() function may fail if:

       EEIINNVVAALL The specified state is not PTHREAD_CANCEL_ENABLE or
              PTHREAD_CANCEL_DISABLE.

       The _p_t_h_r_e_a_d___s_e_t_c_a_n_c_e_l_t_y_p_e() function may fail if:

       EEIINNVVAALL The specified type is not PTHREAD_CANCEL_DEFERRED or
              PTHREAD_CANCEL_ASYNCHRONOUS.

       These functions shall not return an error code of [[EEIINNTTRR]].

       _T_h_e _f_o_l_l_o_w_i_n_g _s_e_c_t_i_o_n_s _a_r_e _i_n_f_o_r_m_a_t_i_v_e_.

EEXXAAMMPPLLEESS
       None.

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       In order to write a signal handler for an asynchronous signal which can
       run safely in a cancellable thread, _p_t_h_r_e_a_d___s_e_t_c_a_n_c_e_l_s_t_a_t_e() must be
       used to disable cancellation for the duration of any calls that the
       signal handler makes which are cancellation points. However, the
       standard does not permit strictly conforming applications to call
       _p_t_h_r_e_a_d___s_e_t_c_a_n_c_e_l_s_t_a_t_e() from a signal handler since it is not
       currently required to be async-signal-safe. On implementations where
       _p_t_h_r_e_a_d___s_e_t_c_a_n_c_e_l_s_t_a_t_e() is not async-signal-safe, alternatives are to
       ensure either that the corresponding signals are blocked during
       execution of functions that are not async-cancel-safe or that
       cancellation is disabled during times when those signals could be
       delivered. Implementations are strongly encouraged to make
       _p_t_h_r_e_a_d___s_e_t_c_a_n_c_e_l_s_t_a_t_e() async-signal-safe.

RRAATTIIOONNAALLEE
       The _p_t_h_r_e_a_d___s_e_t_c_a_n_c_e_l_s_t_a_t_e() and _p_t_h_r_e_a_d___s_e_t_c_a_n_c_e_l_t_y_p_e() functions
       control the points at which a thread may be asynchronously canceled.
       For cancellation control to be usable in modular fashion, some rules
       need to be followed.

       An object can be considered to be a generalization of a procedure. It
       is a set of procedures and global variables written as a unit and
       called by clients not known by the object. Objects may depend on other
       objects.

       First, cancelability should only be disabled on entry to an object,
       never explicitly enabled. On exit from an object, the cancelability
       state should always be restored to its value on entry to the object.

       This follows from a modularity argument: if the client of an object (or
       the client of an object that uses that object) has disabled
       cancelability, it is because the client does not want to be concerned
       about cleaning up if the thread is canceled while executing some
       sequence of actions. If an object is called in such a state and it
       enables cancelability and a cancellation request is pending for that
       thread, then the thread is canceled, contrary to the wish of the client
       that disabled.

       Second, the cancelability type may be explicitly set to either _d_e_f_e_r_r_e_d
       or _a_s_y_n_c_h_r_o_n_o_u_s upon entry to an object. But as with the cancelability
       state, on exit from an object the cancelability type should always be
       restored to its value on entry to the object.

       Finally, only functions that are cancel-safe may be called from a
       thread that is asynchronously cancelable.

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       The _p_t_h_r_e_a_d___s_e_t_c_a_n_c_e_l_s_t_a_t_e() function may be added to the table of
       async-signal-safe functions in _S_e_c_t_i_o_n _2_._4_._3, _S_i_g_n_a_l _A_c_t_i_o_n_s.

SSEEEE AALLSSOO
       _p_t_h_r_e_a_d___c_a_n_c_e_l()

       The Base Definitions volume of POSIX.1-2017, <<pptthhrreeaadd..hh>>

CCOOPPYYRRIIGGHHTT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  In the event of any discrepancy between this version and the
       original IEEE and The Open Group Standard, the original IEEE and The
       Open Group Standard is the referee document. The original Standard can
       be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017            PTHREAD_SETCANCELSTATE(3)
