| #ifndef BOOST_INTERPROCESS_SYNC_XSI_SIMPLE_XSI_SEMAPHORE_HPP |
| #define BOOST_INTERPROCESS_SYNC_XSI_SIMPLE_XSI_SEMAPHORE_HPP |
| |
| /* |
| * 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. |
| */ |
| |
| #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 simple_sem_open_or_create(::key_t key, int initval, int &semid, int perm) |
| { |
| int id, semval; |
| 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 |
| |
| again: |
| if ((id = ::semget(key, 1, (perm & 0x01FF) | IPC_CREAT)) < 0) |
| return false; //permission problem or tables full |
| |
| semid = id; |
| 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 simple_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 simple_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 { |