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-rw-r--r--db2/mutex/mutex.c280
1 files changed, 280 insertions, 0 deletions
diff --git a/db2/mutex/mutex.c b/db2/mutex/mutex.c
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+++ b/db2/mutex/mutex.c
@@ -0,0 +1,280 @@
+/*-
+ * See the file LICENSE for redistribution information.
+ *
+ * Copyright (c) 1996, 1997
+ * Sleepycat Software. All rights reserved.
+ */
+
+#include "config.h"
+
+#ifndef lint
+static const char sccsid[] = "@(#)mutex.c 10.22 (Sleepycat) 8/21/97";
+#endif /* not lint */
+
+#ifndef NO_SYSTEM_INCLUDES
+#include <sys/types.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#endif
+
+#include "db_int.h"
+#include "common_ext.h"
+
+#ifdef HAVE_SPINLOCKS
+
+#ifdef HAVE_FUNC_AIX
+#define TSL_INIT(x)
+#define TSL_SET(x) (!_check_lock(x, 0, 1))
+#define TSL_UNSET(x) _clear_lock(x, 0)
+#endif
+
+#ifdef HAVE_ASSEM_MC68020_GCC
+#include "68020.gcc"
+#endif
+
+#if defined(HAVE_FUNC_MSEM)
+/*
+ * XXX
+ * Should we not use MSEM_IF_NOWAIT and let the system block for us?
+ * I've no idea if this will block all threads in the process or not.
+ */
+#define TSL_INIT(x) msem_init(x, MSEM_UNLOCKED)
+#define TSL_SET(x) (!msem_lock(x, MSEM_IF_NOWAIT))
+#define TSL_UNSET(x) msem_unlock(x, 0)
+#endif
+
+#ifdef HAVE_FUNC_SGI
+#define TSL_INIT(x) init_lock(x)
+#define TSL_SET(x) (!acquire_lock(x))
+#define TSL_UNSET(x) release_lock(x)
+#endif
+
+#ifdef HAVE_FUNC_SOLARIS
+/*
+ * Semaphore calls don't work on Solaris 5.5.
+ *
+ * #define TSL_INIT(x) sema_init(x, 1, USYNC_PROCESS, NULL)
+ * #define TSL_SET(x) (sema_wait(x) == 0)
+ * #define TSL_UNSET(x) sema_post(x)
+ */
+#define TSL_INIT(x)
+#define TSL_SET(x) (_lock_try(x))
+#define TSL_UNSET(x) _lock_clear(x)
+#endif
+
+#ifdef HAVE_ASSEM_SPARC_GCC
+#include "sparc.gcc"
+#endif
+
+#ifdef HAVE_ASSEM_UTS4_CC
+#define TSL_INIT(x)
+#define TSL_SET(x) (!uts_lock(x, 1))
+#define TSL_UNSET(x) (*(x) = 0)
+#endif
+
+#ifdef HAVE_ASSEM_X86_GCC
+#include "x86.gcc"
+#endif
+
+#if defined(_WIN32)
+/* DBDB this needs to be byte-aligned!! */
+#define TSL_INIT(tsl)
+#define TSL_SET(tsl) (!InterlockedExchange((PLONG)tsl, 1))
+#define TSL_UNSET(tsl) (*(tsl) = 0)
+#endif
+
+#ifdef macintosh
+/* Mac spinlocks are simple because we cannot possibly be preempted. */
+#define TSL_INIT(tsl)
+#define TSL_SET(tsl) (*(tsl) = 1)
+#define TSL_UNSET(tsl) (*(tsl) = 0)
+#endif
+
+#endif /* HAVE_SPINLOCKS */
+
+#ifdef MORE_THAN_ONE_PROCESSOR
+#define TSL_DEFAULT_SPINS 5 /* Default spins before block. */
+#else
+#define TSL_DEFAULT_SPINS 1 /* Default spins before block. */
+#endif
+
+/*
+ * __db_mutex_init --
+ * Initialize a DB mutex structure.
+ *
+ * PUBLIC: void __db_mutex_init __P((db_mutex_t *, off_t));
+ */
+void
+__db_mutex_init(mp, off)
+ db_mutex_t *mp;
+ off_t off;
+{
+#ifdef DEBUG
+ if ((ALIGNTYPE)mp & (MUTEX_ALIGNMENT - 1)) {
+ (void)fprintf(stderr,
+ "MUTEX ERROR: mutex NOT %d-byte aligned!\n",
+ MUTEX_ALIGNMENT);
+ abort();
+ }
+#endif
+ memset(mp, 0, sizeof(db_mutex_t));
+
+#ifdef HAVE_SPINLOCKS
+ TSL_INIT(&mp->tsl_resource);
+#else
+ mp->off = off;
+#endif
+}
+
+#define MS(n) ((n) * 1000) /* Milliseconds to micro-seconds. */
+#define SECOND (MS(1000)) /* A second's worth of micro-seconds. */
+
+/*
+ * __db_mutex_lock
+ * Lock on a mutex, logically blocking if necessary.
+ *
+ * PUBLIC: int __db_mutex_lock __P((db_mutex_t *, int, int (*)(void)));
+ */
+int
+__db_mutex_lock(mp, fd, yield)
+ db_mutex_t *mp;
+ int fd;
+ int (*yield) __P((void));
+{
+ u_long usecs;
+
+#ifdef HAVE_SPINLOCKS
+ int nspins;
+
+ for (usecs = MS(10);;) {
+ /*
+ * Try and acquire the uncontested resource lock for
+ * TSL_DEFAULT_SPINS.
+ */
+ for (nspins = TSL_DEFAULT_SPINS; nspins > 0; --nspins)
+ if (TSL_SET(&mp->tsl_resource)) {
+#ifdef DEBUG
+ if (mp->pid != 0) {
+ (void)fprintf(stderr,
+ "MUTEX ERROR: __db_mutex_lock: lock currently locked\n");
+ abort();
+ }
+ mp->pid = getpid();
+#endif
+#ifdef MUTEX_STATISTICS
+ if (usecs == MS(10))
+ ++mp->mutex_set_nowait;
+ else
+ ++mp->mutex_set_wait;
+#endif
+ return (0);
+ }
+
+ /* Yield the processor; wait 10ms initially, up to 1 second. */
+ if (yield == NULL || yield() != 0) {
+ (void)__db_sleep(0, usecs);
+ if ((usecs <<= 1) > SECOND)
+ usecs = SECOND;
+ }
+ }
+ /* NOTREACHED */
+
+#else /* !HAVE_SPINLOCKS */
+ struct flock k_lock;
+ pid_t mypid;
+ int locked;
+
+ /* Initialize the lock. */
+ k_lock.l_whence = SEEK_SET;
+ k_lock.l_start = mp->off;
+ k_lock.l_len = 1;
+
+ for (locked = 0, mypid = getpid();;) {
+ /*
+ * Wait for the lock to become available; wait 10ms initially,
+ * up to 1 second.
+ */
+ for (usecs = MS(10); mp->pid != 0;)
+ if (yield == NULL || yield() != 0) {
+ (void)__db_sleep(0, usecs);
+ if ((usecs <<= 1) > SECOND)
+ usecs = SECOND;
+ }
+
+ /* Acquire an exclusive kernel lock. */
+ k_lock.l_type = F_WRLCK;
+ if (fcntl(fd, F_SETLKW, &k_lock))
+ return (1);
+
+ /* If the resource tsl is still available, it's ours. */
+ if (mp->pid == 0) {
+ locked = 1;
+ mp->pid = mypid;
+ }
+
+ /* Release the kernel lock. */
+ k_lock.l_type = F_UNLCK;
+ if (fcntl(fd, F_SETLK, &k_lock))
+ return (1);
+
+ /*
+ * If we got the resource tsl we're done.
+ *
+ * !!!
+ * We can't check to see if the lock is ours, because we may
+ * be trying to block ourselves in the lock manager, and so
+ * the holder of the lock that's preventing us from getting
+ * the lock may be us! (Seriously.)
+ */
+ if (locked)
+ break;
+ }
+
+#ifdef MUTEX_STATISTICS
+ ++mp->mutex_set_wait;
+#endif
+ return (0);
+#endif /* !HAVE_SPINLOCKS */
+}
+
+/*
+ * __db_mutex_unlock --
+ * Release a lock.
+ *
+ * PUBLIC: int __db_mutex_unlock __P((db_mutex_t *, int));
+ */
+int
+__db_mutex_unlock(mp, fd)
+ db_mutex_t *mp;
+ int fd;
+{
+#ifdef DEBUG
+ if (mp->pid == 0) {
+ (void)fprintf(stderr,
+ "MUTEX ERROR: __db_mutex_unlock: lock already unlocked\n");
+ abort();
+ }
+#endif
+
+#ifdef HAVE_SPINLOCKS
+#ifdef DEBUG
+ mp->pid = 0;
+#endif
+
+ /* Release the resource tsl. */
+ TSL_UNSET(&mp->tsl_resource);
+#else
+ /*
+ * Release the resource tsl. We don't have to acquire any locks
+ * because processes trying to acquire the lock are checking for
+ * a pid of 0, not a specific value.
+ */
+ mp->pid = 0;
+#endif
+ return (0);
+}