Logo Search packages:      
Sourcecode: db3 version File versions  Download package

mutex.h

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996, 1997, 1998, 1999, 2000
 *    Sleepycat Software.  All rights reserved.
 *
 * $Id: mutex.h,v 11.41 2000/12/22 19:28:15 bostic Exp $
 */

/*
 * Some of the Berkeley DB ports require single-threading at various
 * places in the code.  In those cases, these #defines will be set.
 */
#define     DB_BEGIN_SINGLE_THREAD
#define     DB_END_SINGLE_THREAD

/*
 * When the underlying system mutexes require system resources, we have
 * to clean up after application failure.  This violates the rule that
 * we never look at a shared region after a failure, but there's no other
 * choice.  In those cases, this #define is set.
 */
#ifdef HAVE_QNX
#define     MUTEX_SYSTEM_RESOURCES
#endif

/*********************************************************************
 * POSIX.1 pthreads interface.
 *********************************************************************/
#ifdef HAVE_MUTEX_PTHREADS
#include <pthread.h>

#define     MUTEX_FIELDS                                          \
      pthread_mutex_t mutex;        /* Mutex. */                  \
      pthread_cond_t  cond;         /* Condition variable. */
#endif

/*********************************************************************
 * Solaris lwp threads interface.
 *
 * !!!
 * We use LWP mutexes on Solaris instead of UI or POSIX mutexes (both of
 * which are available), for two reasons.  First, the Solaris C library
 * includes versions of the both UI and POSIX thread mutex interfaces, but
 * they are broken in that they don't support inter-process locking, and
 * there's no way to detect it, e.g., calls to configure the mutexes for
 * inter-process locking succeed without error.  So, we use LWP mutexes so
 * that we don't fail in fairly undetectable ways because the application
 * wasn't linked with the appropriate threads library.  Second, there were
 * bugs in SunOS 5.7 (Solaris 7) where if an application loaded the C library
 * before loading the libthread/libpthread threads libraries (e.g., by using
 * dlopen to load the DB library), the pwrite64 interface would be translated
 * into a call to pwrite and DB would drop core.
 *********************************************************************/
#ifdef HAVE_MUTEX_SOLARIS_LWP
/*
 * XXX
 * Don't change <synch.h> to <sys/lwp.h> -- although lwp.h is listed in the
 * Solaris manual page as the correct include to use, it causes the Solaris
 * compiler on SunOS 2.6 to fail.
 */
#include <synch.h>

#define     MUTEX_FIELDS                                          \
      lwp_mutex_t mutex;            /* Mutex. */                  \
      lwp_cond_t cond;        /* Condition variable. */
#endif

/*********************************************************************
 * Solaris/Unixware threads interface.
 *********************************************************************/
#ifdef HAVE_MUTEX_UI_THREADS
#include <thread.h>
#include <synch.h>

#define     MUTEX_FIELDS                                          \
      mutex_t mutex;                /* Mutex. */                  \
      cond_t  cond;                 /* Condition variable. */
#endif

/*********************************************************************
 * AIX C library functions.
 *********************************************************************/
#ifdef HAVE_MUTEX_AIX_CHECK_LOCK
#include <sys/atomic_op.h>
typedef int tsl_t;
#define     MUTEX_ALIGN sizeof(int)

#ifdef LOAD_ACTUAL_MUTEX_CODE
#define     MUTEX_INIT(x)     0
#define     MUTEX_SET(x)      (!_check_lock(x, 0, 1))
#define     MUTEX_UNSET(x)    _clear_lock(x, 0)
#endif
#endif

/*********************************************************************
 * General C library functions (msemaphore).
 *
 * !!!
 * Check for HPPA as a special case, because it requires unusual alignment,
 * and doesn't support semaphores in malloc(3) or shmget(2) memory.
 *
 * !!!
 * Do not remove the MSEM_IF_NOWAIT flag.  The problem is that if a single
 * process makes two msem_lock() calls in a row, the second one returns an
 * error.  We depend on the fact that we can lock against ourselves in the
 * locking subsystem, where we set up a mutex so that we can block ourselves.
 * Tested on OSF1 v4.0.
 *********************************************************************/
#ifdef HAVE_MUTEX_HPPA_MSEM_INIT
#define     MUTEX_NO_MALLOC_LOCKS
#define     MUTEX_NO_SHMGET_LOCKS

#define     MUTEX_ALIGN 16
#endif

#if defined(HAVE_MUTEX_MSEM_INIT) || defined(HAVE_MUTEX_HPPA_MSEM_INIT)
#include <sys/mman.h>
typedef msemaphore tsl_t;

#ifndef MUTEX_ALIGN
#define     MUTEX_ALIGN sizeof(int)
#endif

#ifdef LOAD_ACTUAL_MUTEX_CODE
#define     MUTEX_INIT(x)     (msem_init(x, MSEM_UNLOCKED) <= (msemaphore *)0)
#define     MUTEX_SET(x)      (!msem_lock(x, MSEM_IF_NOWAIT))
#define     MUTEX_UNSET(x)    msem_unlock(x, 0)
#endif
#endif

/*********************************************************************
 * Plan 9 library functions.
 *********************************************************************/
#ifdef HAVE_MUTEX_PLAN9
typedef Lock tsl_t;

#define     MUTEX_ALIGN sizeof(int)

#define     MUTEX_INIT(x)     (memset(x, 0, sizeof(Lock)), 0)
#define     MUTEX_SET(x)      canlock(x)
#define     MUTEX_UNSET(x)    unlock(x)
#endif

/*********************************************************************
 * Reliant UNIX C library functions.
 *********************************************************************/
#ifdef HAVE_MUTEX_RELIANTUNIX_INITSPIN
#include <ulocks.h>
typedef spinlock_t tsl_t;

#ifdef LOAD_ACTUAL_MUTEX_CODE
#define     MUTEX_INIT(x)     (initspin(x, 1), 0)
#define     MUTEX_SET(x)      (cspinlock(x) == 0)
#define     MUTEX_UNSET(x)    spinunlock(x)
#endif
#endif

/*********************************************************************
 * General C library functions (POSIX 1003.1 sema_XXX).
 *
 * !!!
 * Never selected by autoconfig in this release (semaphore calls are known
 * to not work in Solaris 5.5).
 *********************************************************************/
#ifdef HAVE_MUTEX_SEMA_INIT
#include <synch.h>
typedef sema_t tsl_t;
#define     MUTEX_ALIGN  sizeof(int)

#ifdef LOAD_ACTUAL_MUTEX_CODE
#define     MUTEX_DESTROY(x) sema_destroy(x)
#define     MUTEX_INIT(x)      (sema_init(x, 1, USYNC_PROCESS, NULL) != 0)
#define     MUTEX_SET(x)       (sema_wait(x) == 0)
#define     MUTEX_UNSET(x)     sema_post(x)
#endif
#endif

/*********************************************************************
 * SGI C library functions.
 *********************************************************************/
#ifdef HAVE_MUTEX_SGI_INIT_LOCK
#include <abi_mutex.h>
typedef abilock_t tsl_t;
#define     MUTEX_ALIGN sizeof(int)

#ifdef LOAD_ACTUAL_MUTEX_CODE
#define     MUTEX_INIT(x)     (init_lock(x) != 0)
#define     MUTEX_SET(x)      (!acquire_lock(x))
#define     MUTEX_UNSET(x)    release_lock(x)
#endif
#endif

/*********************************************************************
 * Solaris C library functions.
 *
 * !!!
 * These are undocumented functions, but they're the only ones that work
 * correctly as far as we know.
 *********************************************************************/
#ifdef HAVE_MUTEX_SOLARIS_LOCK_TRY
#include <sys/machlock.h>
typedef lock_t tsl_t;
#define     MUTEX_ALIGN sizeof(int)

#ifdef LOAD_ACTUAL_MUTEX_CODE
#define     MUTEX_INIT(x)     0
#define     MUTEX_SET(x)      _lock_try(x)
#define     MUTEX_UNSET(x)    _lock_clear(x)
#endif
#endif

/*********************************************************************
 * VMS.
 *********************************************************************/
#ifdef HAVE_MUTEX_VMS
#include <sys/mman.h>;
#include <builtins.h>
typedef unsigned char tsl_t;
#define     MUTEX_ALIGN       sizeof(unsigned int)

#ifdef LOAD_ACTUAL_MUTEX_CODE
#ifdef __ALPHA
#define     MUTEX_SET(tsl)          (!__TESTBITSSI(tsl, 0))
#else /* __VAX */
#define     MUTEX_SET(tsl)          (!(int)_BBSSI(0, tsl))
#endif
#define     MUTEX_UNSET(tsl)  (*(tsl) = 0)
#define     MUTEX_INIT(tsl)         MUTEX_UNSET(tsl)
#endif
#endif

/*********************************************************************
 * VxWorks
 * Use basic binary semaphores in VxWorks, as we currently do not need
 * any special features.  We do need the ability to single-thread the
 * entire system, however, because VxWorks doesn't support the open(2)
 * flag O_EXCL, the mechanism we normally use to single thread access
 * when we're first looking for a DB environment.
 *********************************************************************/
#ifdef HAVE_MUTEX_VXWORKS
#define     MUTEX_SYSTEM_RESOURCES

#include "semLib.h"
typedef SEM_ID tsl_t;
#define     MUTEX_ALIGN       sizeof(unsigned int)

#ifdef LOAD_ACTUAL_MUTEX_CODE
#define     MUTEX_SET(tsl)          (semTake((*tsl), WAIT_FOREVER) == OK)
#define     MUTEX_UNSET(tsl)  (semGive((*tsl)) == OK)
#define     MUTEX_INIT(tsl)                                       \
      ((*(tsl) = semBCreate(SEM_Q_FIFO, SEM_FULL)) == NULL)
#define     MUTEX_DESTROY(tsl)      semDelete(*tsl)
#endif

/*
 * Use the taskLock() mutex to eliminate a race where two tasks are
 * trying to initialize the global lock at the same time.
 */
#undef      DB_BEGIN_SINGLE_THREAD
#define     DB_BEGIN_SINGLE_THREAD                                \
do {                                                  \
      if (DB_GLOBAL(db_global_init))                              \
            (void)semTake(DB_GLOBAL(db_global_lock), WAIT_FOREVER);     \
      else {                                                \
            taskLock();                               \
            if (DB_GLOBAL(db_global_init)) {                \
                  taskUnlock();                             \
                  (void)semTake(DB_GLOBAL(db_global_lock),  \
                      WAIT_FOREVER);                        \
                  continue;                           \
            }                                         \
            DB_GLOBAL(db_global_lock) =                     \
                semBCreate(SEM_Q_FIFO, SEM_EMPTY);                \
            if (DB_GLOBAL(db_global_lock) != NULL)                \
                  DB_GLOBAL(db_global_init) = 1;                  \
            taskUnlock();                                   \
      }                                               \
} while (DB_GLOBAL(db_global_init) == 0)
#undef      DB_END_SINGLE_THREAD
#define     DB_END_SINGLE_THREAD    (void)semGive(DB_GLOBAL(db_global_lock))
#endif

/*********************************************************************
 * Win16
 *
 * Win16 spinlocks are simple because we cannot possibly be preempted.
 *
 * !!!
 * We should simplify this by always returning a no-need-to-lock lock
 * when we initialize the mutex.
 *********************************************************************/
#ifdef HAVE_MUTEX_WIN16
typedef unsigned int tsl_t;
#define     MUTEX_ALIGN       sizeof(unsigned int)

#ifdef LOAD_ACTUAL_MUTEX_CODE
#define     MUTEX_INIT(x)           0
#define     MUTEX_SET(tsl)          (*(tsl) = 1)
#define     MUTEX_UNSET(tsl)  (*(tsl) = 0)
#endif
#endif

/*********************************************************************
 * Win32
 *********************************************************************/
#ifdef HAVE_MUTEX_WIN32
typedef unsigned int tsl_t;
#define     MUTEX_ALIGN       sizeof(unsigned int)

#ifdef LOAD_ACTUAL_MUTEX_CODE
#define     MUTEX_INIT(x)           0
#define     MUTEX_SET(tsl)          (!InterlockedExchange((PLONG)tsl, 1))
#define     MUTEX_UNSET(tsl)  (*(tsl) = 0)
#endif
#endif

/*********************************************************************
 * 68K/gcc assembly.
 *********************************************************************/
#ifdef HAVE_MUTEX_68K_GCC_ASSEMBLY
typedef unsigned char tsl_t;

#ifdef LOAD_ACTUAL_MUTEX_CODE
/*
 * For gcc/68K, 0 is clear, 1 is set.
 */
#define     MUTEX_SET(tsl) ({                               \
      register tsl_t *__l = (tsl);                          \
      int __r;                                        \
          asm volatile("tas  %1; \n                         \
                    seq  %0"                          \
            : "=dm" (__r), "=m" (*__l)                      \
            : "1" (*__l)                                    \
            );                                        \
      __r & 1;                                        \
})

#define     MUTEX_UNSET(tsl)  (*(tsl) = 0)
#define     MUTEX_INIT(tsl)         MUTEX_UNSET(tsl)
#endif
#endif

/*********************************************************************
 * ALPHA/gcc assembly.
 *********************************************************************/
#ifdef HAVE_MUTEX_ALPHA_GCC_ASSEMBLY
typedef u_int32_t tsl_t;
#define     MUTEX_ALIGN 4

#ifdef LOAD_ACTUAL_MUTEX_CODE
/*
 * For gcc/alpha.  Should return 0 if could not acquire the lock, 1 if
 * lock was acquired properly.
 */
#ifdef __GNUC__
static inline int
MUTEX_SET(tsl_t *tsl) {
      register tsl_t *__l = tsl;
      register tsl_t __r;
      asm volatile(
            "1:   ldl_l %0,%2\n"
            "     blbs  %0,2f\n"
            "     or    $31,1,%0\n"
            "     stl_c %0,%1\n"
            "     beq   %0,3f\n"
            "     mb\n"
            "     br    3f\n"
            "2:   xor   %0,%0\n"
            "3:"
            : "=&r"(__r), "=m"(*__l) : "1"(*__l) : "memory");
      return __r;
}

/*
 * Unset mutex. Judging by Alpha Architecture Handbook, the mb instruction
 * might be necessary before unlocking
 */
static inline int
MUTEX_UNSET(tsl_t *tsl) {
      asm volatile("    mb\n");
      return *tsl = 0;
}
#endif

#ifdef __DECC
#include <alpha/builtins.h>
#define     MUTEX_SET(tsl)          (__LOCK_LONG_RETRY((tsl), 1) != 0)
#define     MUTEX_UNSET(tsl)  (*(tsl) = 0)
#endif

#define     MUTEX_INIT(tsl)         MUTEX_UNSET(tsl)
#endif
#endif

/*********************************************************************
 * HPPA/gcc assembly.
 *********************************************************************/
#ifdef HAVE_MUTEX_HPPA_GCC_ASSEMBLY
typedef u_int32_t tsl_t;
#define     MUTEX_ALIGN 16

#ifdef LOAD_ACTUAL_MUTEX_CODE
/*
 * The PA-RISC has a "load and clear" instead of a "test and set" instruction.
 * The 32-bit word used by that instruction must be 16-byte aligned.  We could
 * use the "aligned" attribute in GCC but that doesn't work for stack variables.
 */
#define     MUTEX_SET(tsl) ({                               \
      register tsl_t *__l = (tsl);                          \
      int __r;                                        \
      asm volatile("ldcws 0(%1),%0" : "=r" (__r) : "r" (__l));    \
      __r & 1;                                        \
})

#define     MUTEX_UNSET(tsl)  (*(tsl) = -1)
#define     MUTEX_INIT(tsl)         MUTEX_UNSET(tsl)
#endif
#endif

/*********************************************************************
 * IA64/gcc assembly.
 *********************************************************************/
#ifdef HAVE_MUTEX_IA64_GCC_ASSEMBLY
typedef unsigned char tsl_t;

#ifdef LOAD_ACTUAL_MUTEX_CODE
/*
 * For gcc/ia64, 0 is clear, 1 is set.
 */
#define     MUTEX_SET(tsl) ({                               \
      register tsl_t *__l = (tsl);                          \
      long __r;                                       \
      asm volatile("xchg1 %0=%1,%3" : "=r"(__r), "=m"(*__l) : "1"(*__l), "r"(1));\
      __r ^ 1;                                        \
})

/*
 * Store through a "volatile" pointer so we get a store with "release"
 * semantics.
 */
#define     MUTEX_UNSET(tsl)  (*(volatile unsigned char *)(tsl) = 0)
#define     MUTEX_INIT(tsl)         MUTEX_UNSET(tsl)
#endif
#endif

/*********************************************************************
 * PowerPC/gcc assembly.
 *********************************************************************/
#ifdef HAVE_MUTEX_PPC_GCC_ASSEMBLY
typedef u_int32_t tsl_t;

#ifdef LOAD_ACTUAL_MUTEX_CODE
/*
 * The PowerPC does a sort of pseudo-atomic locking.  You set up a
 * 'reservation' on a chunk of memory containing a mutex by loading the
 * mutex value with LWARX.  If the mutex has an 'unlocked' (arbitrary)
 * value, you then try storing into it with STWCX.  If no other process or
 * thread broke your 'reservation' by modifying the memory containing the
 * mutex, then the STCWX succeeds; otherwise it fails and you try to get
 * a reservation again.
 *
 * While mutexes are explicitly 4 bytes, a 'reservation' applies to an
 * entire cache line, normally 32 bytes, aligned naturally.  If the mutex
 * lives near data that gets changed a lot, there's a chance that you'll
 * see more broken reservations than you might otherwise.  The only
 * situation in which this might be a problem is if one processor is
 * beating on a variable in the same cache block as the mutex while another
 * processor tries to acquire the mutex.  That's bad news regardless
 * because of the way it bashes caches, but if you can't guarantee that a
 * mutex will reside in a relatively quiescent cache line, you might
 * consider padding the mutex to force it to live in a cache line by
 * itself.  No, you aren't guaranteed that cache lines are 32 bytes.  Some
 * embedded processors use 16-byte cache lines, while some 64-bit
 * processors use 128-bit cache lines.  But assuming a 32-byte cache line
 * won't get you into trouble for now.
 *
 * If mutex locking is a bottleneck, then you can speed it up by adding a
 * regular LWZ load before the LWARX load, so that you can test for the
 * common case of a locked mutex without wasting cycles making a reservation.
 *
 * 'set' mutexes have the value 1, like on Intel; the returned value from
 * MUTEX_SET() is 1 if the mutex previously had its low bit set, 0 otherwise.
 */
#define     MUTEX_SET(tsl)    ({          \
      int __one = 1;                \
      int __r;                \
      tsl_t *__l = (tsl);           \
      asm volatile ("               \
0:                            \
      lwarx %0,0,%1;                \
      cmpwi %0,0;             \
      bne 1f;                       \
      stwcx. %2,0,%1;               \
      bne- 0b;                \
1:"                           \
      : "=&r" (__r)                 \
      : "r" (__l), "r" (__one));    \
      __r & 1;                \
})

#define     MUTEX_UNSET(tsl)  (*(tsl) = 0)
#define     MUTEX_INIT(tsl)         MUTEX_UNSET(tsl)
#endif
#endif

/*********************************************************************
 * SCO/cc assembly.
 *********************************************************************/
#ifdef HAVE_MUTEX_SCO_X86_CC_ASSEMBLY
typedef unsigned char tsl_t;

#ifdef LOAD_ACTUAL_MUTEX_CODE
/*
 * UnixWare has threads in libthread, but OpenServer doesn't (yet).
 *
 * For cc/x86, 0 is clear, 1 is set.
 */

#if defined(__USLC__)
asm int
_tsl_set(void *tsl)
{
%mem tsl
      movl  tsl, %ecx
      movl  $1, %eax
      lock
      xchgb (%ecx),%al
      xorl  $1,%eax
}
#endif

#define     MUTEX_SET(tsl)          _tsl_set(tsl)
#define     MUTEX_UNSET(tsl)  (*(tsl) = 0)
#define     MUTEX_INIT(tsl)         MUTEX_UNSET(tsl)
#endif
#endif

/*********************************************************************
 * Sparc/gcc assembly.
 *********************************************************************/
#ifdef HAVE_MUTEX_SPARC_GCC_ASSEMBLY
typedef unsigned char tsl_t;

#ifdef LOAD_ACTUAL_MUTEX_CODE
/*
 *
 * The ldstub instruction takes the location specified by its first argument
 * (a register containing a memory address) and loads its contents into its
 * second argument (a register) and atomically sets the contents the location
 * specified by its first argument to a byte of 1s.  (The value in the second
 * argument is never read, but only overwritten.)
 *
 * The stbar is needed for v8, and is implemented as membar #sync on v9,
 + so is functional there as well.  For v7, stbar may generate an illegal
 + instruction and we have no way to tell what we're running on.  Some
 + operating systems notice and skip this instruction in the fault handler.
 *
 * For gcc/sparc, 0 is clear, 1 is set.
 */
#define     MUTEX_SET(tsl) ({                               \
      register tsl_t *__l = (tsl);                          \
      register tsl_t __r;                                   \
      __asm__ volatile                                \
          ("ldstub [%1],%0; stbar"                          \
          : "=r"( __r) : "r" (__l));                              \
      !__r;                                           \
})

#define     MUTEX_UNSET(tsl)  (*(tsl) = 0)
#define     MUTEX_INIT(tsl)         MUTEX_UNSET(tsl)
#endif
#endif

/*********************************************************************
 * UTS/cc assembly.
 *********************************************************************/
#ifdef HAVE_MUTEX_UTS_CC_ASSEMBLY
typedef int tsl_t;

#define     MUTEX_ALIGN sizeof(int)
#ifdef LOAD_ACTUAL_MUTEX_CODE
#define     MUTEX_INIT(x)     0
#define     MUTEX_SET(x)      (!uts_lock(x, 1))
#define     MUTEX_UNSET(x)    (*(x) = 0)
#endif
#endif

/*********************************************************************
 * x86/gcc assembly.
 *********************************************************************/
#ifdef HAVE_MUTEX_X86_GCC_ASSEMBLY
typedef unsigned char tsl_t;

#ifdef LOAD_ACTUAL_MUTEX_CODE
/*
 * For gcc/x86, 0 is clear, 1 is set.
 */
#define     MUTEX_SET(tsl) ({                               \
      register tsl_t *__l = (tsl);                          \
      int __r;                                        \
      asm volatile("movl $1,%%eax; lock; xchgb %1,%%al; xorl $1,%%eax"\
          : "=&a" (__r), "=m" (*__l)                              \
          : "1" (*__l)                                \
          );                                                \
      __r & 1;                                        \
})

#define     MUTEX_UNSET(tsl)  (*(tsl) = 0)
#define     MUTEX_INIT(tsl)         MUTEX_UNSET(tsl)
#endif
#endif

/*
 * Mutex alignment defaults to one byte.
 *
 * !!!
 * Various systems require different alignments for mutexes (the worst we've
 * seen so far is 16-bytes on some HP architectures).  Malloc(3) is assumed
 * to return reasonable alignment, all other mutex users must ensure proper
 * alignment locally.
 */
#ifndef     MUTEX_ALIGN
#define     MUTEX_ALIGN 1
#endif

/*
 * Mutex destruction defaults to a no-op.
 */
#ifdef LOAD_ACTUAL_MUTEX_CODE
#ifndef     MUTEX_DESTROY
#define     MUTEX_DESTROY(x)
#endif
#endif

#define     MUTEX_IGNORE            0x001 /* Ignore, no lock required. */
#define     MUTEX_INITED            0x002 /* Mutex is successfully initialized */
#define     MUTEX_SELF_BLOCK  0x004 /* Must block self. */
#define     MUTEX_THREAD            0x008 /* Thread-only mutex. */

/* Mutex. */
struct __mutex_t {
#ifdef      HAVE_MUTEX_THREADS
#ifdef      MUTEX_FIELDS
      MUTEX_FIELDS
#else
      tsl_t tas;              /* Test and set. */
#endif
      u_int32_t spins;        /* Spins before block. */
      u_int32_t locked;       /* !0 if locked. */
#else
      u_int32_t off;                /* Byte offset to lock. */
      u_int32_t pid;                /* Lock holder: 0 or process pid. */
#endif
      u_int32_t mutex_set_wait;     /* Granted after wait. */
      u_int32_t mutex_set_nowait;   /* Granted without waiting. */
#ifdef MUTEX_SYSTEM_RESOURCES
      roff_t        reg_off;        /* Shared lock info offset. */
#endif

      u_int8_t  flags;        /* MUTEX_XXX */
};

/* Redirect calls to the correct functions. */
#ifdef HAVE_MUTEX_THREADS
#if defined(HAVE_MUTEX_PTHREADS) || defined(HAVE_MUTEX_SOLARIS_LWP) || defined(HAVE_MUTEX_UI_THREADS)
#define     __db_mutex_init(a, b, c, d)   __db_pthread_mutex_init(a, b, d)
#define     __db_mutex_lock(a, b, c)      __db_pthread_mutex_lock(a, b)
#define     __db_mutex_unlock(a, b)       __db_pthread_mutex_unlock(a, b)
#define     __db_mutex_destroy(a)         __db_pthread_mutex_destroy(a)
#else
#define     __db_mutex_init(a, b, c, d)   __db_tas_mutex_init(a, b, d)
#define     __db_mutex_lock(a, b, c)      __db_tas_mutex_lock(a, b)
#define     __db_mutex_unlock(a, b)       __db_tas_mutex_unlock(a, b)
#define     __db_mutex_destroy(a)         __db_tas_mutex_destroy(a)
#endif
#else
#define     __db_mutex_init(a, b, c, d)   __db_fcntl_mutex_init(a, b, c)
#define     __db_mutex_lock(a, b, c)      __db_fcntl_mutex_lock(a, b, c)
#define     __db_mutex_unlock(a, b)       __db_fcntl_mutex_unlock(a, b)
#define     __db_mutex_destroy(a)         __db_fcntl_mutex_destroy(a)
#endif

/* Redirect system resource calls to correct functions */
#ifdef MUTEX_SYSTEM_RESOURCES
#define     __db_maintinit(a, b, c)       __db_shreg_maintinit(a, b, c)
#define     __db_shlocks_clear(a, b, c)   __db_shreg_locks_clear(a, b, c)
#define     __db_shlocks_destroy(a, b)    __db_shreg_locks_destroy(a, b)
#define     __db_shmutex_init(a, b, c, d, e, f) \
    __db_shreg_mutex_init(a, b, c, d, e, f)
#else
#define     __db_maintinit(a, b, c)
#define     __db_shlocks_clear(a, b, c)
#define     __db_shlocks_destroy(a, b)
#define     __db_shmutex_init(a, b, c, d, e, f) __db_mutex_init(a, b, c, d)
#endif

/*
 * Lock/unlock a mutex.  If the mutex was marked as uninteresting, the thread
 * of control can proceed without it.
 *
 * If the lock is for threads-only, then it was optionally not allocated and
 * file handles aren't necessary, as threaded applications aren't supported by
 * fcntl(2) locking.
 */
#ifdef DIAGNOSTIC
      /*
       * XXX
       * We want to switch threads as often as possible.  Yield every time
       * we get a mutex to ensure contention.
       */
#define     MUTEX_LOCK(dbenv, mp, fh)                             \
      if (!F_ISSET((MUTEX *)(mp), MUTEX_IGNORE))                  \
            (void)__db_mutex_lock(dbenv, mp, fh);                 \
      if (DB_GLOBAL(db_pageyield))                          \
            __os_yield(NULL, 1);
#else
#define     MUTEX_LOCK(dbenv, mp, fh)                             \
      if (!F_ISSET((MUTEX *)(mp), MUTEX_IGNORE))                  \
            (void)__db_mutex_lock(dbenv, mp, fh);
#endif
#define     MUTEX_UNLOCK(dbenv, mp)                               \
      if (!F_ISSET((MUTEX *)(mp), MUTEX_IGNORE))                  \
            (void)__db_mutex_unlock(dbenv, mp);
#define     MUTEX_THREAD_LOCK(dbenv, mp)                          \
      if (mp != NULL)                                       \
            MUTEX_LOCK(dbenv, mp, NULL)
#define     MUTEX_THREAD_UNLOCK(dbenv, mp)                              \
      if (mp != NULL)                                       \
            MUTEX_UNLOCK(dbenv, mp)

/*
 * We use a single file descriptor for fcntl(2) locking, and (generally) the
 * object's offset in a shared region as the byte that we're locking.  So,
 * there's a (remote) possibility that two objects might have the same offsets
 * such that the locks could conflict, resulting in deadlock.  To avoid this
 * possibility, we offset the region offset by a small integer value, using a
 * different offset for each subsystem's locks.  Since all region objects are
 * suitably aligned, the offset guarantees that we don't collide with another
 * region's objects.
 */
#define     DB_FCNTL_OFF_GEN  0           /* Everything else. */
#define     DB_FCNTL_OFF_LOCK 1           /* Lock subsystem offset. */
#define     DB_FCNTL_OFF_MPOOL      2           /* Mpool subsystem offset. */

Generated by  Doxygen 1.6.0   Back to index