PTHREAD_COND_DESTROY(3)    POSIX Programmer's Manual   PTHREAD_COND_DESTROY(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_cond_destroy, pthread_cond_init -- destroy and initialize
       condition variables

SSYYNNOOPPSSIISS
       #include <pthread.h>

       int pthread_cond_destroy(pthread_cond_t *_c_o_n_d);
       int pthread_cond_init(pthread_cond_t *restrict _c_o_n_d,
           const pthread_condattr_t *restrict _a_t_t_r);
       pthread_cond_t _c_o_n_d = PTHREAD_COND_INITIALIZER;

DDEESSCCRRIIPPTTIIOONN
       The _p_t_h_r_e_a_d___c_o_n_d___d_e_s_t_r_o_y() function shall destroy the given condition
       variable specified by _c_o_n_d; the object becomes, in effect,
       uninitialized. An implementation may cause _p_t_h_r_e_a_d___c_o_n_d___d_e_s_t_r_o_y() to
       set the object referenced by _c_o_n_d to an invalid value. A destroyed
       condition variable object can be reinitialized using
       _p_t_h_r_e_a_d___c_o_n_d___i_n_i_t(); the results of otherwise referencing the object
       after it has been destroyed are undefined.

       It shall be safe to destroy an initialized condition variable upon
       which no threads are currently blocked. Attempting to destroy a
       condition variable upon which other threads are currently blocked
       results in undefined behavior.

       The _p_t_h_r_e_a_d___c_o_n_d___i_n_i_t() function shall initialize the condition
       variable referenced by _c_o_n_d with attributes referenced by _a_t_t_r.  If
       _a_t_t_r is NULL, the default condition variable attributes shall be used;
       the effect is the same as passing the address of a default condition
       variable attributes object. Upon successful initialization, the state
       of the condition variable shall become initialized.

       See _S_e_c_t_i_o_n _2_._9_._9, _S_y_n_c_h_r_o_n_i_z_a_t_i_o_n _O_b_j_e_c_t _C_o_p_i_e_s _a_n_d _A_l_t_e_r_n_a_t_i_v_e
       _M_a_p_p_i_n_g_s for further requirements.

       Attempting to initialize an already initialized condition variable
       results in undefined behavior.

       In cases where default condition variable attributes are appropriate,
       the macro PTHREAD_COND_INITIALIZER can be used to initialize condition
       variables. The effect shall be equivalent to dynamic initialization by
       a call to _p_t_h_r_e_a_d___c_o_n_d___i_n_i_t() with parameter _a_t_t_r specified as NULL,
       except that no error checks are performed.

       The behavior is undefined if the value specified by the _c_o_n_d argument
       to _p_t_h_r_e_a_d___c_o_n_d___d_e_s_t_r_o_y() does not refer to an initialized condition
       variable.

       The behavior is undefined if the value specified by the _a_t_t_r argument
       to _p_t_h_r_e_a_d___c_o_n_d___i_n_i_t() does not refer to an initialized condition
       variable attributes object.

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

EERRRROORRSS
       The _p_t_h_r_e_a_d___c_o_n_d___i_n_i_t() function shall fail if:

       EEAAGGAAIINN The system lacked the necessary resources (other than memory) to
              initialize another condition variable.

       EENNOOMMEEMM Insufficient memory exists to initialize the condition variable.

       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
       A condition variable can be destroyed immediately after all the threads
       that are blocked on it are awakened. For example, consider the
       following code:


           struct list {
               pthread_mutex_t lm;
               ...
           }

           struct elt {
               key k;
               int busy;
               pthread_cond_t notbusy;
               ...
           }

           /* Find a list element and reserve it. */
           struct elt *
           list_find(struct list *lp, key k)
           {
               struct elt *ep;

               pthread_mutex_lock(&lp->lm);
               while ((ep = find_elt(l, k) != NULL) && ep->busy)
                   pthread_cond_wait(&ep->notbusy, &lp->lm);
               if (ep != NULL)
                   ep->busy = 1;
               pthread_mutex_unlock(&lp->lm);
               return(ep);
           }

           delete_elt(struct list *lp, struct elt *ep)
           {
               pthread_mutex_lock(&lp->lm);
               assert(ep->busy);
               ... remove ep from list ...
               ep->busy = 0;  /* Paranoid. */
           (A) pthread_cond_broadcast(&ep->notbusy);
               pthread_mutex_unlock(&lp->lm);
           (B) pthread_cond_destroy(&ep->notbusy);
               free(ep);
           }

       In this example, the condition variable and its list element may be
       freed (line B) immediately after all threads waiting for it are
       awakened (line A), since the mutex and the code ensure that no other
       thread can touch the element to be deleted.

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       None.

RRAATTIIOONNAALLEE
       If an implementation detects that the value specified by the _c_o_n_d
       argument to _p_t_h_r_e_a_d___c_o_n_d___d_e_s_t_r_o_y() does not refer to an initialized
       condition variable, it is recommended that the function should fail and
       report an [[EEIINNVVAALL]] error.

       If an implementation detects that the value specified by the _c_o_n_d
       argument to _p_t_h_r_e_a_d___c_o_n_d___d_e_s_t_r_o_y() or _p_t_h_r_e_a_d___c_o_n_d___i_n_i_t() refers to a
       condition variable that is in use (for example, in a
       _p_t_h_r_e_a_d___c_o_n_d___w_a_i_t() call) by another thread, or detects that the value
       specified by the _c_o_n_d argument to _p_t_h_r_e_a_d___c_o_n_d___i_n_i_t() refers to an
       already initialized condition variable, it is recommended that the
       function should fail and report an [[EEBBUUSSYY]] error.

       If an implementation detects that the value specified by the _a_t_t_r
       argument to _p_t_h_r_e_a_d___c_o_n_d___i_n_i_t() does not refer to an initialized
       condition variable attributes object, it is recommended that the
       function should fail and report an [[EEIINNVVAALL]] error.

       See also _p_t_h_r_e_a_d___m_u_t_e_x___d_e_s_t_r_o_y().

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       None.

SSEEEE AALLSSOO
       _p_t_h_r_e_a_d___c_o_n_d___b_r_o_a_d_c_a_s_t(), _p_t_h_r_e_a_d___c_o_n_d___t_i_m_e_d_w_a_i_t(),
       _p_t_h_r_e_a_d___m_u_t_e_x___d_e_s_t_r_o_y()

       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_COND_DESTROY(3)
