/*------------------------------------------------------------------------- * * s_lock.h * Hardware-dependent implementation of spinlocks. * * NOTE: none of the macros in this file are intended to be called directly. * Call them through the hardware-independent macros in spin.h. * * The following hardware-dependent macros must be provided for each * supported platform: * * void S_INIT_LOCK(slock_t *lock) * Initialize a spinlock (to the unlocked state). * * void S_LOCK(slock_t *lock) * Acquire a spinlock, waiting if necessary. * Time out and abort() if unable to acquire the lock in a * "reasonable" amount of time --- typically ~ 1 minute. * * void S_UNLOCK(slock_t *lock) * Unlock a previously acquired lock. * * bool S_LOCK_FREE(slock_t *lock) * Tests if the lock is free. Returns TRUE if free, FALSE if locked. * This does *not* change the state of the lock. * * void SPIN_DELAY(void) * Delay operation to occur inside spinlock wait loop. * * Note to implementors: there are default implementations for all these * macros at the bottom of the file. Check if your platform can use * these or needs to override them. * * Usually, S_LOCK() is implemented in terms of an even lower-level macro * TAS(): * * int TAS(slock_t *lock) * Atomic test-and-set instruction. Attempt to acquire the lock, * but do *not* wait. Returns 0 if successful, nonzero if unable * to acquire the lock. * * TAS() is NOT part of the API, and should never be called directly. * * CAUTION: on some platforms TAS() may sometimes report failure to acquire * a lock even when the lock is not locked. For example, on Alpha TAS() * will "fail" if interrupted. Therefore TAS() should always be invoked * in a retry loop, even if you are certain the lock is free. * * ANOTHER CAUTION: be sure that TAS() and S_UNLOCK() represent sequence * points, ie, loads and stores of other values must not be moved across * a lock or unlock. In most cases it suffices to make the operation be * done through a "volatile" pointer. * * On most supported platforms, TAS() uses a tas() function written * in assembly language to execute a hardware atomic-test-and-set * instruction. Equivalent OS-supplied mutex routines could be used too. * * If no system-specific TAS() is available (ie, HAVE_SPINLOCKS is not * defined), then we fall back on an emulation that uses SysV semaphores * (see spin.c). This emulation will be MUCH MUCH slower than a proper TAS() * implementation, because of the cost of a kernel call per lock or unlock. * An old report is that Postgres spends around 40% of its time in semop(2) * when using the SysV semaphore code. * * * Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * $PostgreSQL: pgsql/src/include/storage/s_lock.h,v 1.132 2004/10/06 23:41:59 neilc Exp $ * *------------------------------------------------------------------------- */ #ifndef S_LOCK_H #define S_LOCK_H #include "storage/pg_sema.h" #ifdef HAVE_SPINLOCKS /* skip spinlocks if requested */ #if defined(__GNUC__) || defined(__ICC) /************************************************************************* * All the gcc inlines * Gcc consistently defines the CPU as __cpu__. * Other compilers use __cpu or __cpu__ so we test for both in those cases. */ /*---------- * Standard gcc asm format (assuming "volatile slock_t *lock"): __asm__ __volatile__( " instruction \n" " instruction \n" " instruction \n" : "=r"(_res), "+m"(*lock) // return register, in/out lock value : "r"(lock) // lock pointer, in input register : "memory", "cc"); // show clobbered registers here * The output-operands list (after first colon) should always include * "+m"(*lock), whether or not the asm code actually refers to this * operand directly. This ensures that gcc believes the value in the * lock variable is used and set by the asm code. Also, the clobbers * list (after third colon) should always include "memory"; this prevents * gcc from thinking it can cache the values of shared-memory fields * across the asm code. Add "cc" if your asm code changes the condition * code register, and also list any temp registers the code uses. *---------- */ #if defined(__i386__) || defined(__x86_64__) /* AMD Opteron */ #define HAS_TEST_AND_SET typedef unsigned char slock_t; #define TAS(lock) tas(lock) static __inline__ int tas(volatile slock_t *lock) { register slock_t _res = 1; /* Use a non-locking test before asserting the bus lock */ __asm__ __volatile__( " cmpb $0,%1 \n" " jne 1f \n" " lock \n" " xchgb %0,%1 \n" "1: \n" : "+q"(_res), "+m"(*lock) : : "memory", "cc"); return (int) _res; } #define SPIN_DELAY() spin_delay() static __inline__ void spin_delay(void) { /* * This sequence is equivalent to the PAUSE instruction ("rep" is * ignored by old IA32 processors if the following instruction is * not a string operation); the IA-32 Architecture Software * Developer's Manual, Vol. 3, Section 7.7.2 describes why using * PAUSE in the inner loop of a spin lock is necessary for good * performance: * * The PAUSE instruction improves the performance of IA-32 * processors supporting Hyper-Threading Technology when * executing spin-wait loops and other routines where one * thread is accessing a shared lock or semaphore in a tight * polling loop. When executing a spin-wait loop, the * processor can suffer a severe performance penalty when * exiting the loop because it detects a possible memory order * violation and flushes the core processor's pipeline. The * PAUSE instruction provides a hint to the processor that the * code sequence is a spin-wait loop. The processor uses this * hint to avoid the memory order violation and prevent the * pipeline flush. In addition, the PAUSE instruction * de-pipelines the spin-wait loop to prevent it from * consuming execution resources excessively. */ __asm__ __volatile__( " rep; nop \n"); } #endif /* __i386__ || __x86_64__ */ #if defined(__ia64__) || defined(__ia64) /* __ia64 used by ICC compiler? */ /* Intel Itanium */ #define HAS_TEST_AND_SET typedef unsigned int slock_t; #define TAS(lock) tas(lock) static __inline__ int tas(volatile slock_t *lock) { long int ret; __asm__ __volatile__( " xchg4 %0=%1,%2 \n" : "=r"(ret), "+m"(*lock) : "r"(1) : "memory"); return (int) ret; } #endif /* __ia64__ || __ia64 */ #if defined(__arm__) || defined(__arm) #define HAS_TEST_AND_SET typedef unsigned char slock_t; #define TAS(lock) tas(lock) static __inline__ int tas(volatile slock_t *lock) { register slock_t _res = 1; __asm__ __volatile__( " swpb %0, %0, [%2] \n" : "+r"(_res), "+m"(*lock) : "r"(lock) : "memory"); return (int) _res; } #endif /* __arm__ */ #if defined(__s390__) || defined(__s390x__) /* S/390 and S/390x Linux (32- and 64-bit zSeries) */ #define HAS_TEST_AND_SET typedef unsigned int slock_t; #define TAS(lock) tas(lock) static __inline__ int tas(volatile slock_t *lock) { int _res = 0; __asm__ __volatile__( " cs %0,%3,0(%2) \n" : "+d"(_res), "+m"(*lock) : "a"(lock), "d"(1) : "memory", "cc"); return _res; } #endif /* __s390__ || __s390x__ */ #if defined(__sparc__) #define HAS_TEST_AND_SET typedef unsigned char slock_t; #define TAS(lock) tas(lock) static __inline__ int tas(volatile slock_t *lock) { register slock_t _res; __asm__ __volatile__( " ldstub [%2], %0 \n" : "=r"(_res), "+m"(*lock) : "r"(lock) : "memory"); return (int) _res; } #endif /* __sparc__ */ #if defined(__ppc__) || defined(__powerpc__) || defined(__powerpc64__) #define HAS_TEST_AND_SET #if defined(__powerpc64__) typedef unsigned long slock_t; #else typedef unsigned int slock_t; #endif #define TAS(lock) tas(lock) /* * NOTE: per the Enhanced PowerPC Architecture manual, v1.0 dated 7-May-2002, * an isync is a sufficient synchronization barrier after a lwarx/stwcx loop. */ static __inline__ int tas(volatile slock_t *lock) { slock_t _t; int _res; __asm__ __volatile__( " lwarx %0,0,%3 \n" " cmpwi %0,0 \n" " bne 1f \n" " addi %0,%0,1 \n" " stwcx. %0,0,%3 \n" " beq 2f \n" "1: li %1,1 \n" " b 3f \n" "2: \n" " isync \n" " li %1,0 \n" "3: \n" : "=&r"(_t), "=r"(_res), "+m"(*lock) : "r"(lock) : "memory", "cc"); return _res; } /* PowerPC S_UNLOCK is almost standard but requires a "sync" instruction */ #define S_UNLOCK(lock) \ do \ {\ __asm__ __volatile__ (" sync \n"); \ *((volatile slock_t *) (lock)) = 0; \ } while (0) #endif /* powerpc */ #if defined(__mc68000__) && defined(__linux__) #define HAS_TEST_AND_SET typedef unsigned char slock_t; #define TAS(lock) tas(lock) static __inline__ int tas(volatile slock_t *lock) { register int rv; __asm__ __volatile__( " clrl %0 \n" " tas %1 \n" " sne %0 \n" : "=d"(rv), "+m"(*lock) : : "memory", "cc"); return rv; } #endif /* defined(__mc68000__) && defined(__linux__) */ #if defined(__vax__) /* * VAXen -- even multiprocessor ones * (thanks to Tom Ivar Helbekkmo) */ #define HAS_TEST_AND_SET typedef unsigned char slock_t; #define TAS(lock) tas(lock) static __inline__ int tas(volatile slock_t *lock) { register int _res; __asm__ __volatile__( " movl $1, %0 \n" " bbssi $0, (%2), 1f \n" " clrl %0 \n" "1: \n" : "=&r"(_res), "+m"(*lock) : "r"(lock) : "memory"); return _res; } #endif /* __vax__ */ #if defined(__ns32k__) #define HAS_TEST_AND_SET typedef unsigned char slock_t; #define TAS(lock) tas(lock) static __inline__ int tas(volatile slock_t *lock) { register int _res; __asm__ __volatile__( " sbitb 0, %1 \n" " sfsd %0 \n" : "=r"(_res), "+m"(*lock) : : "memory"); return _res; } #endif /* __ns32k__ */ #if defined(__alpha) || defined(__alpha__) /* * Correct multi-processor locking methods are explained in section 5.5.3 * of the Alpha AXP Architecture Handbook, which at this writing can be * found at ftp://ftp.netbsd.org/pub/NetBSD/misc/dec-docs/index.html. * For gcc we implement the handbook's code directly with inline assembler. */ #define HAS_TEST_AND_SET typedef unsigned long slock_t; #define TAS(lock) tas(lock) static __inline__ int tas(volatile slock_t *lock) { register slock_t _res; __asm__ __volatile__( " ldq $0, %1 \n" " bne $0, 2f \n" " ldq_l %0, %1 \n" " bne %0, 2f \n" " mov 1, $0 \n" " stq_c $0, %1 \n" " beq $0, 2f \n" " mb \n" " br 3f \n" "2: mov 1, %0 \n" "3: \n" : "=&r"(_res), "+m"(*lock) : : "memory", "0"); return (int) _res; } #define S_UNLOCK(lock) \ do \ {\ __asm__ __volatile__ (" mb \n"); \ *((volatile slock_t *) (lock)) = 0; \ } while (0) #endif /* __alpha || __alpha__ */ /* These live in s_lock.c, but only for gcc */ #if defined(__m68k__) #define HAS_TEST_AND_SET typedef unsigned char slock_t; #endif #if defined(__mips__) && !defined(__sgi) #define HAS_TEST_AND_SET typedef unsigned int slock_t; #endif #endif /* __GNUC__ */ /*************************************************************************** * Platforms that use non-gcc inline assembly: */ #if !defined(HAS_TEST_AND_SET) /* We didn't trigger above, let's try here */ #if defined(USE_UNIVEL_CC) #define HAS_TEST_AND_SET typedef unsigned char slock_t; #define TAS(lock) tas(lock) asm int tas(volatile slock_t *s_lock) { /* UNIVEL wants %mem in column 1, so we don't pg_indent this file */ %mem s_lock pushl %ebx movl s_lock, %ebx movl $255, %eax lock xchgb %al, (%ebx) popl %ebx } #endif /* defined(USE_UNIVEL_CC) */ #if defined(__alpha) || defined(__alpha__) /* * The Tru64 compiler doesn't support gcc-style inline asm, but it does * have some builtin functions that accomplish much the same results. * For simplicity, slock_t is defined as long (ie, quadword) on Alpha * regardless of the compiler in use. LOCK_LONG and UNLOCK_LONG only * operate on an int (ie, longword), but that's OK as long as we define * S_INIT_LOCK to zero out the whole quadword. */ #define HAS_TEST_AND_SET typedef unsigned long slock_t; #include #define S_INIT_LOCK(lock) (*(lock) = 0) #define TAS(lock) (__LOCK_LONG_RETRY((lock), 1) == 0) #define S_UNLOCK(lock) __UNLOCK_LONG(lock) #endif /* __alpha || __alpha__ */ #if defined(__hppa) || defined(__hppa__) /* * HP's PA-RISC * * See src/backend/port/hpux/tas.c.template for details about LDCWX. Because * LDCWX requires a 16-byte-aligned address, we declare slock_t as a 16-byte * struct. The active word in the struct is whichever has the aligned address; * the other three words just sit at -1. * * When using gcc, we can inline the required assembly code. */ #define HAS_TEST_AND_SET typedef struct { int sema[4]; } slock_t; #define TAS_ACTIVE_WORD(lock) ((volatile int *) (((long) (lock) + 15) & ~15)) #if defined(__GNUC__) static __inline__ int tas(volatile slock_t *lock) { volatile int *lockword = TAS_ACTIVE_WORD(lock); register int lockval; __asm__ __volatile__( " ldcwx 0(0,%2),%0 \n" : "=r"(lockval), "+m"(*lockword) : "r"(lockword) : "memory"); return (lockval == 0); } #endif /* __GNUC__ */ #define S_UNLOCK(lock) (*TAS_ACTIVE_WORD(lock) = -1) #define S_INIT_LOCK(lock) \ do { \ volatile slock_t *lock_ = (lock); \ lock_->sema[0] = -1; \ lock_->sema[1] = -1; \ lock_->sema[2] = -1; \ lock_->sema[3] = -1; \ } while (0) #define S_LOCK_FREE(lock) (*TAS_ACTIVE_WORD(lock) != 0) #endif /* __hppa || __hppa__ */ #if defined(__hpux) && defined(__ia64) && !defined(__GNUC__) #define HAS_TEST_AND_SET typedef unsigned int slock_t; #include #define TAS(lock) _Asm_xchg(_SZ_W, lock, 1, _LDHINT_NONE) #endif /* HPUX on IA64, non gcc */ #if defined(__QNX__) && defined(__WATCOMC__) /* * QNX 4 using WATCOM C */ #define HAS_TEST_AND_SET typedef unsigned char slock_t; #define TAS(lock) wc_tas(lock) extern slock_t wc_tas(volatile slock_t *lock); #pragma aux wc_tas =\ " mov al,1 " \ " lock xchg al,[esi]" \ parm [esi] \ value [al]; #endif /* __QNX__ and __WATCOMC__*/ #if defined(__sgi) /* * SGI IRIX 5 * slock_t is defined as a unsigned long. We use the standard SGI * mutex API. * * The following comment is left for historical reasons, but is probably * not a good idea since the mutex ABI is supported. * * This stuff may be supplemented in the future with Masato Kataoka's MIPS-II * assembly from his NECEWS SVR4 port, but we probably ought to retain this * for the R3000 chips out there. */ #define HAS_TEST_AND_SET typedef unsigned long slock_t; #include "mutex.h" #define TAS(lock) (test_and_set(lock,1)) #define S_UNLOCK(lock) (test_then_and(lock,0)) #define S_INIT_LOCK(lock) (test_then_and(lock,0)) #define S_LOCK_FREE(lock) (test_then_add(lock,0) == 0) #endif /* __sgi */ #if defined(sinix) /* * SINIX / Reliant UNIX * slock_t is defined as a struct abilock_t, which has a single unsigned long * member. (Basically same as SGI) */ #define HAS_TEST_AND_SET #include "abi_mutex.h" typedef abilock_t slock_t; #define TAS(lock) (!acquire_lock(lock)) #define S_UNLOCK(lock) release_lock(lock) #define S_INIT_LOCK(lock) init_lock(lock) #define S_LOCK_FREE(lock) (stat_lock(lock) == UNLOCKED) #endif /* sinix */ #if defined(_AIX) /* * AIX (POWER) */ #define HAS_TEST_AND_SET typedef unsigned int slock_t; #define TAS(lock) _check_lock(lock, 0, 1) #define S_UNLOCK(lock) _clear_lock(lock, 0) #endif /* _AIX */ #if defined (nextstep) #define HAS_TEST_AND_SET typedef struct mutex slock_t; #define S_LOCK(lock) mutex_lock(lock) #define S_UNLOCK(lock) mutex_unlock(lock) #define S_INIT_LOCK(lock) mutex_init(lock) /* For Mach, we have to delve inside the entrails of `struct mutex'. Ick! */ #define S_LOCK_FREE(alock) ((alock)->lock == 0) #endif /* nextstep */ /* These are in s_lock.c */ #if defined(sun3) #define HAS_TEST_AND_SET typedef unsigned char slock_t; #endif #if defined(__sparc__) || defined(__sparc) #define HAS_TEST_AND_SET typedef unsigned char slock_t; #endif /* out-of-line assembler from src/backend/port/tas/foo.s */ #if defined(__sun) && defined(__i386) /* * Solaris/386 (we only get here for non-gcc case) */ #define HAS_TEST_AND_SET typedef unsigned char slock_t; #endif #endif /* !defined(HAS_TEST_AND_SET) */ /* Blow up if we didn't have any way to do spinlocks */ #ifndef HAS_TEST_AND_SET #error PostgreSQL does not have native spinlock support on this platform. To continue the compilation, rerun configure using --disable-spinlocks. However, performance will be poor. Please report this to pgsql-bugs@postgresql.org. #endif #else /* !HAVE_SPINLOCKS */ /* * Fake spinlock implementation using semaphores --- slow and prone * to fall foul of kernel limits on number of semaphores, so don't use this * unless you must! The subroutines appear in spin.c. */ typedef PGSemaphoreData slock_t; extern bool s_lock_free_sema(volatile slock_t *lock); extern void s_unlock_sema(volatile slock_t *lock); extern void s_init_lock_sema(volatile slock_t *lock); extern int tas_sema(volatile slock_t *lock); #define S_LOCK_FREE(lock) s_lock_free_sema(lock) #define S_UNLOCK(lock) s_unlock_sema(lock) #define S_INIT_LOCK(lock) s_init_lock_sema(lock) #define TAS(lock) tas_sema(lock) #endif /* HAVE_SPINLOCKS */ /* * Default Definitions - override these above as needed. */ #if !defined(S_LOCK) #define S_LOCK(lock) \ do { \ if (TAS(lock)) \ s_lock((lock), __FILE__, __LINE__); \ } while (0) #endif /* S_LOCK */ #if !defined(S_LOCK_FREE) #define S_LOCK_FREE(lock) (*(lock) == 0) #endif /* S_LOCK_FREE */ #if !defined(S_UNLOCK) #define S_UNLOCK(lock) (*((volatile slock_t *) (lock)) = 0) #endif /* S_UNLOCK */ #if !defined(S_INIT_LOCK) #define S_INIT_LOCK(lock) S_UNLOCK(lock) #endif /* S_INIT_LOCK */ #if !defined(SPIN_DELAY) #define SPIN_DELAY() ((void) 0) #endif /* SPIN_DELAY */ #if !defined(TAS) extern int tas(volatile slock_t *lock); /* in port/.../tas.s, or * s_lock.c */ #define TAS(lock) tas(lock) #endif /* TAS */ /* * Platform-independent out-of-line support routines */ extern void s_lock(volatile slock_t *lock, const char *file, int line); #endif /* S_LOCK_H */