This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       Applications using these functions may be subject  to  priority  inversion,  as  discussed  in  the  Base
       Definitions volume of POSIX.1‐2017, Section3.291, PriorityInversion.

       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(3POSIX)

       The  sem_trywait() function shall lock the semaphore referenced by sem 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  sem_wait()  function  shall  lock  the  semaphore  referenced  by sem 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 sem_wait() 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
       sem_post() function is executed and returns successfully.

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

       The sem_trywait() function shall fail if:

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

       The sem_trywait() and sem_wait() functions may fail if:

       EDEADLK
              A deadlock condition was detected.

       EINTR  A signal interrupted this function.

       EINVAL The sem argument does not refer to a valid semaphore.

       Thefollowingsectionsareinformative.

       None.

       None.

       sem_trywait, sem_wait — lock a semaphore

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

       None.

       The  sem_trywait()  and  sem_wait()  functions  shall  return  zero  if  the calling process successfully
       performed the semaphore lock operation on the semaphore designated by sem.  If the call was unsuccessful,
       the state of the semaphore shall be unchanged, and the function shall return a value of -1 and set  errno
       to indicate the error.

semctl(), semget(), semop(), sem_post(), sem_timedwait()

       The  Base  Definitions  volume  of  POSIX.1‐2017, Section3.291, PriorityInversion, Section4.12, MemorySynchronization, <semaphore.h>

       #include <semaphore.h>

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