SEM_TRYWAIT(3)             POSIX Programmer's Manual            SEM_TRYWAIT(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
       sem_trywait, sem_wait -- lock a semaphore

SSYYNNOOPPSSIISS
       #include <semaphore.h>

       int sem_trywait(sem_t *_s_e_m);
       int sem_wait(sem_t *_s_e_m);

DDEESSCCRRIIPPTTIIOONN
       The _s_e_m___t_r_y_w_a_i_t() function shall lock the semaphore referenced by _s_e_m
       only if the semaphore is currently not locked; that is, if the
       semaphore value is currently positive. Otherwise, it shall not lock the
       semaphore.

       The _s_e_m___w_a_i_t() function shall lock the semaphore referenced by _s_e_m by
       performing a semaphore lock operation on that semaphore. If the
       semaphore value is currently zero, then the calling thread shall not
       return from the call to _s_e_m___w_a_i_t() until it either locks the semaphore
       or the call is interrupted by a signal.

       Upon successful return, the state of the semaphore shall be locked and
       shall remain locked until the _s_e_m___p_o_s_t() function is executed and
       returns successfully.

       The _s_e_m___w_a_i_t() function is interruptible by the delivery of a signal.

RREETTUURRNN VVAALLUUEE
       The _s_e_m___t_r_y_w_a_i_t() and _s_e_m___w_a_i_t() functions shall return zero if the
       calling process successfully performed the semaphore lock operation on
       the semaphore designated by _s_e_m.  If the call was unsuccessful, the
       state of the semaphore shall be unchanged, and the function shall
       return a value of -1 and set _e_r_r_n_o to indicate the error.

EERRRROORRSS
       The _s_e_m___t_r_y_w_a_i_t() function shall fail if:

       EEAAGGAAIINN The semaphore was already locked, so it cannot be immediately
              locked by the _s_e_m___t_r_y_w_a_i_t() operation.

       The _s_e_m___t_r_y_w_a_i_t() and _s_e_m___w_a_i_t() functions may fail if:

       EEDDEEAADDLLKK
              A deadlock condition was detected.

       EEIINNTTRR  A signal interrupted this function.

       EEIINNVVAALL The _s_e_m argument does not refer to a valid semaphore.

       _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
       Applications using these functions may be subject to priority
       inversion, as discussed in the Base Definitions volume of POSIX.1-2017,
       _S_e_c_t_i_o_n _3_._2_9_1, _P_r_i_o_r_i_t_y _I_n_v_e_r_s_i_o_n.

RRAATTIIOONNAALLEE
       None.

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       None.

SSEEEE AALLSSOO
       _s_e_m_c_t_l(), _s_e_m_g_e_t(), _s_e_m_o_p(), _s_e_m___p_o_s_t(), _s_e_m___t_i_m_e_d_w_a_i_t()

       The Base Definitions volume of POSIX.1-2017, _S_e_c_t_i_o_n _3_._2_9_1, _P_r_i_o_r_i_t_y
       _I_n_v_e_r_s_i_o_n, _S_e_c_t_i_o_n _4_._1_2, _M_e_m_o_r_y _S_y_n_c_h_r_o_n_i_z_a_t_i_o_n, <<sseemmaapphhoorree..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                       SEM_TRYWAIT(3)
