diff options
Diffstat (limited to 'src/backend/port/sysv_sema.c')
| -rw-r--r-- | src/backend/port/sysv_sema.c | 126 |
1 files changed, 60 insertions, 66 deletions
diff --git a/src/backend/port/sysv_sema.c b/src/backend/port/sysv_sema.c index 1d44a40033c..d42e8c87684 100644 --- a/src/backend/port/sysv_sema.c +++ b/src/backend/port/sysv_sema.c @@ -8,7 +8,7 @@ * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/port/sysv_sema.c,v 1.16 2004/12/31 22:00:29 pgsql Exp $ + * $PostgreSQL: pgsql/src/backend/port/sysv_sema.c,v 1.17 2005/10/15 02:49:22 momjian Exp $ * *------------------------------------------------------------------------- */ @@ -58,8 +58,7 @@ typedef int IpcSemaphoreId; /* semaphore ID returned by semget(2) */ #define PGSemaMagic 537 /* must be less than SEMVMX */ -static IpcSemaphoreId *mySemaSets; /* IDs of sema sets acquired so - * far */ +static IpcSemaphoreId *mySemaSets; /* IDs of sema sets acquired so far */ static int numSemaSets; /* number of sema sets acquired so far */ static int maxSemaSets; /* allocated size of mySemaSets array */ static IpcSemaphoreKey nextSemaKey; /* next key to try using */ @@ -97,11 +96,10 @@ InternalIpcSemaphoreCreate(IpcSemaphoreKey semKey, int numSems) if (semId < 0) { /* - * Fail quietly if error indicates a collision with existing set. - * One would expect EEXIST, given that we said IPC_EXCL, but - * perhaps we could get a permission violation instead? Also, - * EIDRM might occur if an old set is slated for destruction but - * not gone yet. + * Fail quietly if error indicates a collision with existing set. One + * would expect EEXIST, given that we said IPC_EXCL, but perhaps we + * could get a permission violation instead? Also, EIDRM might occur + * if an old set is slated for destruction but not gone yet. */ if (errno == EEXIST || errno == EACCES #ifdef EIDRM @@ -120,13 +118,13 @@ InternalIpcSemaphoreCreate(IpcSemaphoreKey semKey, int numSems) IPC_CREAT | IPC_EXCL | IPCProtection), (errno == ENOSPC) ? errhint("This error does *not* mean that you have run out of disk space.\n" - "It occurs when either the system limit for the maximum number of " - "semaphore sets (SEMMNI), or the system wide maximum number of " - "semaphores (SEMMNS), would be exceeded. You need to raise the " - "respective kernel parameter. Alternatively, reduce PostgreSQL's " - "consumption of semaphores by reducing its max_connections parameter " + "It occurs when either the system limit for the maximum number of " + "semaphore sets (SEMMNI), or the system wide maximum number of " + "semaphores (SEMMNS), would be exceeded. You need to raise the " + "respective kernel parameter. Alternatively, reduce PostgreSQL's " + "consumption of semaphores by reducing its max_connections parameter " "(currently %d).\n" - "The PostgreSQL documentation contains more information about " + "The PostgreSQL documentation contains more information about " "configuring your system for PostgreSQL.", MaxBackends) : 0)); } @@ -149,7 +147,7 @@ IpcSemaphoreInitialize(IpcSemaphoreId semId, int semNum, int value) semId, semNum, value), (errno == ERANGE) ? errhint("You possibly need to raise your kernel's SEMVMX value to be at least " - "%d. Look into the PostgreSQL documentation for details.", + "%d. Look into the PostgreSQL documentation for details.", value) : 0)); } @@ -224,8 +222,8 @@ IpcSemaphoreCreate(int numSems) continue; /* sema belongs to a non-Postgres app */ /* - * If the creator PID is my own PID or does not belong to any - * extant process, it's safe to zap it. + * If the creator PID is my own PID or does not belong to any extant + * process, it's safe to zap it. */ creatorPID = IpcSemaphoreGetLastPID(semId, numSems); if (creatorPID <= 0) @@ -237,11 +235,10 @@ IpcSemaphoreCreate(int numSems) } /* - * The sema set appears to be from a dead Postgres process, or - * from a previous cycle of life in this same process. Zap it, if - * possible. This probably shouldn't fail, but if it does, assume - * the sema set belongs to someone else after all, and continue - * quietly. + * The sema set appears to be from a dead Postgres process, or from a + * previous cycle of life in this same process. Zap it, if possible. + * This probably shouldn't fail, but if it does, assume the sema set + * belongs to someone else after all, and continue quietly. */ semun.val = 0; /* unused, but keep compiler quiet */ if (semctl(semId, 0, IPC_RMID, semun) < 0) @@ -255,17 +252,17 @@ IpcSemaphoreCreate(int numSems) break; /* successful create */ /* - * Can only get here if some other process managed to create the - * same sema key before we did. Let him have that one, loop - * around to try next key. + * Can only get here if some other process managed to create the same + * sema key before we did. Let him have that one, loop around to try + * next key. */ } /* - * OK, we created a new sema set. Mark it as created by this process. - * We do this by setting the spare semaphore to PGSemaMagic-1 and then - * incrementing it with semop(). That leaves it with value - * PGSemaMagic and sempid referencing this process. + * OK, we created a new sema set. Mark it as created by this process. We + * do this by setting the spare semaphore to PGSemaMagic-1 and then + * incrementing it with semop(). That leaves it with value PGSemaMagic + * and sempid referencing this process. */ IpcSemaphoreInitialize(semId, numSems, PGSemaMagic - 1); mysema.semId = semId; @@ -303,8 +300,7 @@ PGReserveSemaphores(int maxSemas, int port) elog(PANIC, "out of memory"); numSemaSets = 0; nextSemaKey = port * 1000; - nextSemaNumber = SEMAS_PER_SET; /* force sema set alloc on 1st - * call */ + nextSemaNumber = SEMAS_PER_SET; /* force sema set alloc on 1st call */ on_shmem_exit(ReleaseSemaphores, 0); } @@ -378,38 +374,36 @@ PGSemaphoreLock(PGSemaphore sema, bool interruptOK) sops.sem_num = sema->semNum; /* - * Note: if errStatus is -1 and errno == EINTR then it means we - * returned from the operation prematurely because we were sent a - * signal. So we try and lock the semaphore again. + * Note: if errStatus is -1 and errno == EINTR then it means we returned + * from the operation prematurely because we were sent a signal. So we + * try and lock the semaphore again. * - * Each time around the loop, we check for a cancel/die interrupt. We - * assume that if such an interrupt comes in while we are waiting, it - * will cause the semop() call to exit with errno == EINTR, so that we - * will be able to service the interrupt (if not in a critical section - * already). + * Each time around the loop, we check for a cancel/die interrupt. We assume + * that if such an interrupt comes in while we are waiting, it will cause + * the semop() call to exit with errno == EINTR, so that we will be able + * to service the interrupt (if not in a critical section already). * * Once we acquire the lock, we do NOT check for an interrupt before - * returning. The caller needs to be able to record ownership of the - * lock before any interrupt can be accepted. + * returning. The caller needs to be able to record ownership of the lock + * before any interrupt can be accepted. * - * There is a window of a few instructions between CHECK_FOR_INTERRUPTS - * and entering the semop() call. If a cancel/die interrupt occurs in - * that window, we would fail to notice it until after we acquire the - * lock (or get another interrupt to escape the semop()). We can - * avoid this problem by temporarily setting ImmediateInterruptOK to - * true before we do CHECK_FOR_INTERRUPTS; then, a die() interrupt in - * this interval will execute directly. However, there is a huge - * pitfall: there is another window of a few instructions after the - * semop() before we are able to reset ImmediateInterruptOK. If an - * interrupt occurs then, we'll lose control, which means that the - * lock has been acquired but our caller did not get a chance to - * record the fact. Therefore, we only set ImmediateInterruptOK if the - * caller tells us it's OK to do so, ie, the caller does not need to - * record acquiring the lock. (This is currently true for lockmanager - * locks, since the process that granted us the lock did all the - * necessary state updates. It's not true for SysV semaphores used to - * implement LW locks or emulate spinlocks --- but the wait time for - * such locks should not be very long, anyway.) + * There is a window of a few instructions between CHECK_FOR_INTERRUPTS and + * entering the semop() call. If a cancel/die interrupt occurs in that + * window, we would fail to notice it until after we acquire the lock (or + * get another interrupt to escape the semop()). We can avoid this + * problem by temporarily setting ImmediateInterruptOK to true before we + * do CHECK_FOR_INTERRUPTS; then, a die() interrupt in this interval will + * execute directly. However, there is a huge pitfall: there is another + * window of a few instructions after the semop() before we are able to + * reset ImmediateInterruptOK. If an interrupt occurs then, we'll lose + * control, which means that the lock has been acquired but our caller did + * not get a chance to record the fact. Therefore, we only set + * ImmediateInterruptOK if the caller tells us it's OK to do so, ie, the + * caller does not need to record acquiring the lock. (This is currently + * true for lockmanager locks, since the process that granted us the lock + * did all the necessary state updates. It's not true for SysV semaphores + * used to implement LW locks or emulate spinlocks --- but the wait time + * for such locks should not be very long, anyway.) */ do { @@ -439,10 +433,10 @@ PGSemaphoreUnlock(PGSemaphore sema) sops.sem_num = sema->semNum; /* - * Note: if errStatus is -1 and errno == EINTR then it means we - * returned from the operation prematurely because we were sent a - * signal. So we try and unlock the semaphore again. Not clear this - * can really happen, but might as well cope. + * Note: if errStatus is -1 and errno == EINTR then it means we returned + * from the operation prematurely because we were sent a signal. So we + * try and unlock the semaphore again. Not clear this can really happen, + * but might as well cope. */ do { @@ -469,9 +463,9 @@ PGSemaphoreTryLock(PGSemaphore sema) sops.sem_num = sema->semNum; /* - * Note: if errStatus is -1 and errno == EINTR then it means we - * returned from the operation prematurely because we were sent a - * signal. So we try and lock the semaphore again. + * Note: if errStatus is -1 and errno == EINTR then it means we returned + * from the operation prematurely because we were sent a signal. So we + * try and lock the semaphore again. */ do { |