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Diffstat (limited to 'boost/interprocess/sync/xsi/advanced_xsi_semaphore.hpp')
| -rw-r--r-- | boost/interprocess/sync/xsi/advanced_xsi_semaphore.hpp | 201 |
1 files changed, 0 insertions, 201 deletions
diff --git a/boost/interprocess/sync/xsi/advanced_xsi_semaphore.hpp b/boost/interprocess/sync/xsi/advanced_xsi_semaphore.hpp deleted file mode 100644 index 49562f5cbd..0000000000 --- a/boost/interprocess/sync/xsi/advanced_xsi_semaphore.hpp +++ /dev/null @@ -1,201 +0,0 @@ -/* - * Provide an simpler and easier to understand interface to the System V - * semaphore system calls. There are 7 routines available to the user: - * - * id = sem_create(key, initval); # create with initial value or open - * id = sem_open(key); # open (must already exist) - * sem_wait(id); # wait = P = down by 1 - * sem_signal(id); # signal = V = up by 1 - * sem_op(id, amount); # wait if (amount < 0) - * # signal if (amount > 0) - * sem_close(id); # close - * sem_rm(id); # remove (delete) - * - * We create and use a 3-member set for the requested semaphore. - * The first member, [0], is the actual semaphore value, and the second - * member, [1], is a counter used to know when all processes have finished - * with the semaphore. The counter is initialized to a large number, - * decremented on every create or open and incremented on every close. - * This way we can use the "adjust" feature provided by System V so that - * any process that exit's without calling sem_close() is accounted - * for. It doesn't help us if the last process does this (as we have - * no way of getting control to remove the semaphore) but it will - * work if any process other than the last does an exit (intentional - * or unintentional). - * The third member, [2], of the semaphore set is used as a lock variable - * to avoid any race conditions in the sem_create() and sem_close() - * functions. - */ - -#ifndef BOOST_INTERPROCESS_SYNC_XSI_ADVANCED_XSI_SEMAPHORE_HPP -#define BOOST_INTERPROCESS_SYNC_XSI_ADVANCED_XSI_SEMAPHORE_HPP - -#ifndef BOOST_CONFIG_HPP -# include <boost/config.hpp> -#endif -# -#if defined(BOOST_HAS_PRAGMA_ONCE) -# pragma once -#endif - -#include <sys/ipc.h> -#include <sys/sem.h> -#include <errno.h> - -namespace boost { -namespace interprocess { -namespace xsi { - -// Create a semaphore with a specified initial value. -// If the semaphore already exists, we don't initialize it (of course). -// We return the semaphore ID if all OK, else -1. - -inline bool advanced_sem_open_or_create(::key_t key, int initval, int &semid, int perm) -{ - semid = -1; - int id, semval; - union semun { - int val; - ::semid_ds *buf; - ushort *array; - } semctl_arg; - - if (key == IPC_PRIVATE) - return false; //not intended for private semaphores - - else if (key == (::key_t) -1) - return false; //probably an ftok() error by caller - - again: - if ((id = ::semget(key, 3, (perm & 0x01FF) | IPC_CREAT)) < 0) - return false; //permission problem or tables full - - // When the semaphore is created, we know that the value of all - // 3 members is 0. - // Get a lock on the semaphore by waiting for [2] to equal 0, - // then increment it. - // - // There is a race condition here. There is a possibility that - // between the semget() above and the ::semop() below, another - // process can call our sem_close() function which can remove - // the semaphore if that process is the last one using it. - // Therefore, we handle the error condition of an invalid - // semaphore ID specially below, and if it does happen, we just - // go back and create it again. - struct sembuf op_lock[2] = { - {2, 0, 0}, // wait for [2] (lock) to equal 0 - {2, 1, SEM_UNDO} // then increment [2] to 1 - this locks it - // UNDO to release the lock if processes exits - // before explicitly unlocking - }; - - if (::semop(id, &op_lock[0], 2) < 0) { - if (errno == EINVAL) - goto again; - } - - // Get the value of the process counter. If it equals 0, - // then no one has initialized the semaphore yet. - if ((semval = ::semctl(id, 1, GETVAL, 0)) < 0) - return false; - - if (semval == 0) { - // We could initialize by doing a SETALL, but that - // would clear the adjust value that we set when we - // locked the semaphore above. Instead, we'll do 2 - // system calls to initialize [0] and [1]. - semctl_arg.val = initval; - if (::semctl(id, 0, SETVAL, semctl_arg) < 0) - return false; - - semctl_arg.val = 1; - if (::semctl(id, 1, SETVAL, semctl_arg) < 0) - return false; - } - - // Decrement the process counter and then release the lock. - struct sembuf op_unlock[1] = { - 2, -1, 0/*SEM_UNDO*/ // decrement [2] (lock) back to 0 - }; - - if (::semop(id, &op_unlock[0], 1) < 0) - return false; - - semid = id; - return true; -} - -// Open a semaphore that must already exist. -// This function should be used, instead of sem_create(), if the caller -// knows that the semaphore must already exist. For example a client -// from a client-server pair would use this, if its the server's -// responsibility to create the semaphore. -// We return the semaphore ID if all OK, else -1. -/* -inline bool advanced_sem_open(key_t key, int &semid) -{ - semid = -1; - if (key == IPC_PRIVATE) - return false; // not intended for private semaphores - - else if (key == (::key_t) -1) - return false; // probably an ftok() error by caller - - if ((semid = ::semget(key, 3, 0)) < 0) - return false; // doesn't exist, or tables full - - // Decrement the process counter. We don't need a lock - struct sembuf op_open[1] = { - 1, -1, SEM_UNDO // decrement [1] (proc counter) with undo on exit - }; - - if (::semop(id, &op_open[0], 1) < 0) - return false; - - return true; -} -*/ -/**************************************************************************** - * Remove a semaphore. - * This call is intended to be called by a server, for example, - * when it is being shut down, as we do an IPC_RMID on the semaphore, - * regardless whether other processes may be using it or not. - * Most other processes should use sem_close() below. - */ - -inline bool advanced_sem_rm(int id) -{ - if (::semctl(id, 0, IPC_RMID, 0) < 0) - return false; - return true; -} - - -/**************************************************************************** - * General semaphore operation. Increment or decrement by a user-specified - * amount (positive or negative; amount can't be zero). - */ - -inline bool advanced_sem_op(int id, int value, bool undo = true) -{ - ::sembuf op_op[1] = { - 0, 99, 0 // decrement or increment [0] with undo on exit - // the 99 is set to the actual amount to add - // or subtract (positive or negative) - }; - if(undo){ - op_op[0].sem_flg = SEM_UNDO; - } - if ((op_op[0].sem_op = value) == 0) - return false; - - if (::semop(id, &op_op[0], 1) < 0) - return false; - return true; -} - -} //namespace xsi { -} //namespace interprocess { -} //namespace boost { - -#endif //BOOST_INTERPROCESS_SYNC_XSI_ADVANCED_XSI_SEMAPHORE_HPP |