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postgresql/src/include/storage/s_lock.h

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/*-------------------------------------------------------------------------
*
* 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).
*
* int 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.
* Should return number of "delays"; see s_lock.c
*
* 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 even lower-level macros
* TAS() and TAS_SPIN():
*
* 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.
*
* int TAS_SPIN(slock_t *lock)
* Like TAS(), but this version is used when waiting for a lock
* previously found to be contended. By default, this is the
* same as TAS(), but on some architectures it's better to poll a
* contended lock using an unlocked instruction and retry the
* atomic test-and-set only when it appears free.
*
* TAS() and TAS_SPIN() are NOT part of the API, and should never be called
* directly.
*
* CAUTION: on some platforms TAS() and/or TAS_SPIN() 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 a retry loop must
* always be used, even if you are certain the lock is free.
*
* It is the responsibility of these macros to make sure that the compiler
* does not re-order accesses to shared memory to precede the actual lock
* acquisition, or follow the lock release. Prior to PostgreSQL 9.5, this
* was the caller's responsibility, which meant that callers had to use
* volatile-qualified pointers to refer to both the spinlock itself and the
* shared data being accessed within the spinlocked critical section. This
* was notationally awkward, easy to forget (and thus error-prone), and
* prevented some useful compiler optimizations. For these reasons, we
* now require that the macros themselves prevent compiler re-ordering,
* so that the caller doesn't need to take special precautions.
*
* On platforms with weak memory ordering, the TAS(), TAS_SPIN(), and
* S_UNLOCK() macros must further include hardware-level memory fence
* instructions to prevent similar re-ordering at the hardware level.
* TAS() and TAS_SPIN() must guarantee that loads and stores issued after
* the macro are not executed until the lock has been obtained. Conversely,
* S_UNLOCK() must guarantee that loads and stores issued before the macro
* have been executed before the lock is released.
*
* 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) 1996-2024, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/storage/s_lock.h
*
*-------------------------------------------------------------------------
*/
#ifndef S_LOCK_H
#define S_LOCK_H
#ifdef FRONTEND
#error "s_lock.h may not be included from frontend code"
#endif
#ifdef HAVE_SPINLOCKS /* skip spinlocks if requested */
#if defined(__GNUC__) || defined(__INTEL_COMPILER)
/*************************************************************************
* 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.
*----------
*/
#ifdef __i386__ /* 32-bit i386 */
#define HAS_TEST_AND_SET
typedef unsigned char slock_t;
#define TAS(lock) tas(lock)
static __inline__ int
tas(volatile slock_t *lock)
{
slock_t _res = 1;
/*
* Use a non-locking test before asserting the bus lock. Note that the
* extra test appears to be a small loss on some x86 platforms and a small
* win on others; it's by no means clear that we should keep it.
*
* When this was last tested, we didn't have separate TAS() and TAS_SPIN()
* macros. Nowadays it probably would be better to do a non-locking test
* in TAS_SPIN() but not in TAS(), like on x86_64, but no-one's done the
* testing to verify that. Without some empirical evidence, better to
* leave it alone.
*/
__asm__ __volatile__(
" cmpb $0,%1 \n"
" jne 1f \n"
" lock \n"
" xchgb %0,%1 \n"
"1: \n"
: "+q"(_res), "+m"(*lock)
: /* no inputs */
: "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__ */
#ifdef __x86_64__ /* AMD Opteron, Intel EM64T */
#define HAS_TEST_AND_SET
typedef unsigned char slock_t;
#define TAS(lock) tas(lock)
/*
* On Intel EM64T, it's a win to use a non-locking test before the xchg proper,
* but only when spinning.
*
* See also Implementing Scalable Atomic Locks for Multi-Core Intel(tm) EM64T
* and IA32, by Michael Chynoweth and Mary R. Lee. As of this writing, it is
* available at:
* http://software.intel.com/en-us/articles/implementing-scalable-atomic-locks-for-multi-core-intel-em64t-and-ia32-architectures
*/
#define TAS_SPIN(lock) (*(lock) ? 1 : TAS(lock))
static __inline__ int
tas(volatile slock_t *lock)
{
slock_t _res = 1;
__asm__ __volatile__(
" lock \n"
" xchgb %0,%1 \n"
: "+q"(_res), "+m"(*lock)
: /* no inputs */
: "memory", "cc");
return (int) _res;
}
#define SPIN_DELAY() spin_delay()
static __inline__ void
spin_delay(void)
{
/*
* Adding a PAUSE in the spin delay loop is demonstrably a no-op on
* Opteron, but it may be of some use on EM64T, so we keep it.
*/
__asm__ __volatile__(
" rep; nop \n");
}
#endif /* __x86_64__ */
/*
* On ARM and ARM64, we use __sync_lock_test_and_set(int *, int) if available.
*
* We use the int-width variant of the builtin because it works on more chips
* than other widths.
*/
#if defined(__arm__) || defined(__arm) || defined(__aarch64__)
#ifdef HAVE_GCC__SYNC_INT32_TAS
#define HAS_TEST_AND_SET
#define TAS(lock) tas(lock)
typedef int slock_t;
static __inline__ int
tas(volatile slock_t *lock)
{
return __sync_lock_test_and_set(lock, 1);
}
#define S_UNLOCK(lock) __sync_lock_release(lock)
/*
* Using an ISB instruction to delay in spinlock loops appears beneficial on
* high-core-count ARM64 processors. It seems mostly a wash for smaller gear,
* and ISB doesn't exist at all on pre-v7 ARM chips.
*/
#if defined(__aarch64__)
#define SPIN_DELAY() spin_delay()
static __inline__ void
spin_delay(void)
{
__asm__ __volatile__(
" isb; \n");
}
#endif /* __aarch64__ */
#endif /* HAVE_GCC__SYNC_INT32_TAS */
#endif /* __arm__ || __arm || __aarch64__ */
/* S/390 and S/390x Linux (32- and 64-bit zSeries) */
#if defined(__s390__) || defined(__s390x__)
#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__) /* Sparc */
/*
* Solaris has always run sparc processors in TSO (total store) mode, but
* linux didn't use to and the *BSDs still don't. So, be careful about
* acquire/release semantics. The CPU will treat superfluous members as
* NOPs, so it's just code space.
*/
#define HAS_TEST_AND_SET
typedef unsigned char slock_t;
#define TAS(lock) tas(lock)
static __inline__ int
tas(volatile slock_t *lock)
{
slock_t _res;
/*
* See comment in src/backend/port/tas/sunstudio_sparc.s for why this
* uses "ldstub", and that file uses "cas". gcc currently generates
* sparcv7-targeted binaries, so "cas" use isn't possible.
*/
__asm__ __volatile__(
" ldstub [%2], %0 \n"
: "=r"(_res), "+m"(*lock)
: "r"(lock)
: "memory");
#if defined(__sparcv7) || defined(__sparc_v7__)
/*
* No stbar or membar available, luckily no actually produced hardware
* requires a barrier.
*/
#elif defined(__sparcv8) || defined(__sparc_v8__)
/* stbar is available (and required for both PSO, RMO), membar isn't */
__asm__ __volatile__ ("stbar \n":::"memory");
#else
/*
* #LoadStore (RMO) | #LoadLoad (RMO) together are the appropriate acquire
* barrier for sparcv8+ upwards.
*/
__asm__ __volatile__ ("membar #LoadStore | #LoadLoad \n":::"memory");
#endif
return (int) _res;
}
#if defined(__sparcv7) || defined(__sparc_v7__)
/*
* No stbar or membar available, luckily no actually produced hardware
* requires a barrier. We fall through to the default gcc definition of
* S_UNLOCK in this case.
*/
#elif defined(__sparcv8) || defined(__sparc_v8__)
/* stbar is available (and required for both PSO, RMO), membar isn't */
#define S_UNLOCK(lock) \
do \
{ \
__asm__ __volatile__ ("stbar \n":::"memory"); \
*((volatile slock_t *) (lock)) = 0; \
} while (0)
#else
/*
* #LoadStore (RMO) | #StoreStore (RMO, PSO) together are the appropriate
* release barrier for sparcv8+ upwards.
*/
#define S_UNLOCK(lock) \
do \
{ \
__asm__ __volatile__ ("membar #LoadStore | #StoreStore \n":::"memory"); \
*((volatile slock_t *) (lock)) = 0; \
} while (0)
#endif
#endif /* __sparc__ */
/* PowerPC */
#if defined(__ppc__) || defined(__powerpc__) || defined(__ppc64__) || defined(__powerpc64__)
#define HAS_TEST_AND_SET
typedef unsigned int slock_t;
#define TAS(lock) tas(lock)
/* On PPC, it's a win to use a non-locking test before the lwarx */
#define TAS_SPIN(lock) (*(lock) ? 1 : TAS(lock))
/*
* The second operand of addi can hold a constant zero or a register number,
* hence constraint "=&b" to avoid allocating r0. "b" stands for "address
* base register"; most operands having this register-or-zero property are
* address bases, e.g. the second operand of lwax.
*
* 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.
* But if the spinlock is in ordinary memory, we can use lwsync instead for
* better performance.
*/
static __inline__ int
tas(volatile slock_t *lock)
{
slock_t _t;
int _res;
__asm__ __volatile__(
" lwarx %0,0,%3,1 \n"
" cmpwi %0,0 \n"
" bne 1f \n"
" addi %0,%0,1 \n"
" stwcx. %0,0,%3 \n"
" beq 2f \n"
"1: \n"
" li %1,1 \n"
" b 3f \n"
"2: \n"
" lwsync \n"
" li %1,0 \n"
"3: \n"
: "=&b"(_t), "=r"(_res), "+m"(*lock)
: "r"(lock)
: "memory", "cc");
return _res;
}
/*
* PowerPC S_UNLOCK is almost standard but requires a "sync" instruction.
* But we can use lwsync instead for better performance.
*/
#define S_UNLOCK(lock) \
do \
{ \
__asm__ __volatile__ (" lwsync \n" ::: "memory"); \
*((volatile slock_t *) (lock)) = 0; \
} while (0)
#endif /* powerpc */
#if defined(__mips__) && !defined(__sgi) /* non-SGI MIPS */
#define HAS_TEST_AND_SET
typedef unsigned int slock_t;
#define TAS(lock) tas(lock)
/*
* Original MIPS-I processors lacked the LL/SC instructions, but if we are
* so unfortunate as to be running on one of those, we expect that the kernel
* will handle the illegal-instruction traps and emulate them for us. On
* anything newer (and really, MIPS-I is extinct) LL/SC is the only sane
* choice because any other synchronization method must involve a kernel
* call. Unfortunately, many toolchains still default to MIPS-I as the
* codegen target; if the symbol __mips shows that that's the case, we
* have to force the assembler to accept LL/SC.
*
* R10000 and up processors require a separate SYNC, which has the same
* issues as LL/SC.
*/
#if __mips < 2
#define MIPS_SET_MIPS2 " .set mips2 \n"
#else
#define MIPS_SET_MIPS2
#endif
static __inline__ int
tas(volatile slock_t *lock)
{
volatile slock_t *_l = lock;
int _res;
int _tmp;
__asm__ __volatile__(
" .set push \n"
MIPS_SET_MIPS2
" .set noreorder \n"
" .set nomacro \n"
" ll %0, %2 \n"
" or %1, %0, 1 \n"
" sc %1, %2 \n"
" xori %1, 1 \n"
" or %0, %0, %1 \n"
" sync \n"
" .set pop "
: "=&r" (_res), "=&r" (_tmp), "+R" (*_l)
: /* no inputs */
: "memory");
return _res;
}
/* MIPS S_UNLOCK is almost standard but requires a "sync" instruction */
#define S_UNLOCK(lock) \
do \
{ \
__asm__ __volatile__( \
" .set push \n" \
MIPS_SET_MIPS2 \
" .set noreorder \n" \
" .set nomacro \n" \
" sync \n" \
" .set pop " \
: /* no outputs */ \
: /* no inputs */ \
: "memory"); \
*((volatile slock_t *) (lock)) = 0; \
} while (0)
#endif /* __mips__ && !__sgi */
#if defined(__hppa) || defined(__hppa__) /* HP PA-RISC */
/*
* HP's PA-RISC
*
* 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.
*/
#define HAS_TEST_AND_SET
typedef struct
{
int sema[4];
} slock_t;
#define TAS_ACTIVE_WORD(lock) ((volatile int *) (((uintptr_t) (lock) + 15) & ~15))
static __inline__ int
tas(volatile slock_t *lock)
{
volatile int *lockword = TAS_ACTIVE_WORD(lock);
int lockval;
/*
* The LDCWX instruction atomically clears the target word and
* returns the previous value. Hence, if the instruction returns
* 0, someone else has already acquired the lock before we tested
* it (i.e., we have failed).
*
* Notice that this means that we actually clear the word to set
* the lock and set the word to clear the lock. This is the
* opposite behavior from the SPARC LDSTUB instruction. For some
* reason everything that H-P does is rather baroque...
*
* For details about the LDCWX instruction, see the "Precision
* Architecture and Instruction Reference Manual" (09740-90014 of June
* 1987), p. 5-38.
*/
__asm__ __volatile__(
" ldcwx 0(0,%2),%0 \n"
: "=r"(lockval), "+m"(*lockword)
: "r"(lockword)
: "memory");
return (lockval == 0);
}
#define S_UNLOCK(lock) \
do { \
__asm__ __volatile__("" : : : "memory"); \
*TAS_ACTIVE_WORD(lock) = -1; \
} while (0)
#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 we have no platform-specific knowledge, but we found that the compiler
* provides __sync_lock_test_and_set(), use that. Prefer the int-width
* version over the char-width version if we have both, on the rather dubious
* grounds that that's known to be more likely to work in the ARM ecosystem.
* (But we dealt with ARM above.)
*/
#if !defined(HAS_TEST_AND_SET)
#if defined(HAVE_GCC__SYNC_INT32_TAS)
#define HAS_TEST_AND_SET
#define TAS(lock) tas(lock)
typedef int slock_t;
static __inline__ int
tas(volatile slock_t *lock)
{
return __sync_lock_test_and_set(lock, 1);
}
#define S_UNLOCK(lock) __sync_lock_release(lock)
#elif defined(HAVE_GCC__SYNC_CHAR_TAS)
#define HAS_TEST_AND_SET
#define TAS(lock) tas(lock)
typedef char slock_t;
static __inline__ int
tas(volatile slock_t *lock)
{
return __sync_lock_test_and_set(lock, 1);
}
#define S_UNLOCK(lock) __sync_lock_release(lock)
#endif /* HAVE_GCC__SYNC_INT32_TAS */
#endif /* !defined(HAS_TEST_AND_SET) */
/*
* Default implementation of S_UNLOCK() for gcc/icc.
*
* Note that this implementation is unsafe for any platform that can reorder
* a memory access (either load or store) after a following store. That
* happens not to be possible on x86 and most legacy architectures (some are
* single-processor!), but many modern systems have weaker memory ordering.
* Those that do must define their own version of S_UNLOCK() rather than
* relying on this one.
*/
#if !defined(S_UNLOCK)
#define S_UNLOCK(lock) \
do { __asm__ __volatile__("" : : : "memory"); *(lock) = 0; } while (0)
#endif
#endif /* defined(__GNUC__) || defined(__INTEL_COMPILER) */
/*
* ---------------------------------------------------------------------
* Platforms that use non-gcc inline assembly:
* ---------------------------------------------------------------------
*/
#if !defined(HAS_TEST_AND_SET) /* We didn't trigger above, let's try here */
/* These are in sunstudio_(sparc|x86).s */
#if defined(__SUNPRO_C) && (defined(__i386) || defined(__x86_64__) || defined(__sparc__) || defined(__sparc))
#define HAS_TEST_AND_SET
#if defined(__i386) || defined(__x86_64__) || defined(__sparcv9) || defined(__sparcv8plus)
typedef unsigned int slock_t;
#else
typedef unsigned char slock_t;
#endif
extern slock_t pg_atomic_cas(volatile slock_t *lock, slock_t with,
slock_t cmp);
#define TAS(a) (pg_atomic_cas((a), 1, 0) != 0)
#endif
#ifdef _MSC_VER
typedef LONG slock_t;
#define HAS_TEST_AND_SET
#define TAS(lock) (InterlockedCompareExchange(lock, 1, 0))
#define SPIN_DELAY() spin_delay()
/* If using Visual C++ on Win64, inline assembly is unavailable.
* Use a _mm_pause intrinsic instead of rep nop.
*/
#if defined(_WIN64)
static __forceinline void
spin_delay(void)
{
_mm_pause();
}
#else
static __forceinline void
spin_delay(void)
{
/* See comment for gcc code. Same code, MASM syntax */
__asm rep nop;
}
#endif
#include <intrin.h>
#pragma intrinsic(_ReadWriteBarrier)
#define S_UNLOCK(lock) \
do { _ReadWriteBarrier(); (*(lock)) = 0; } while (0)
#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@lists.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 int 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, bool nested);
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, false)
#define TAS(lock) tas_sema(lock)
#endif /* HAVE_SPINLOCKS */
/*
* Default Definitions - override these above as needed.
*/
#if !defined(S_LOCK)
#define S_LOCK(lock) \
(TAS(lock) ? s_lock((lock), __FILE__, __LINE__, __func__) : 0)
#endif /* S_LOCK */
#if !defined(S_LOCK_FREE)
#define S_LOCK_FREE(lock) (*(lock) == 0)
#endif /* S_LOCK_FREE */
#if !defined(S_UNLOCK)
/*
* Our default implementation of S_UNLOCK is essentially *(lock) = 0. This
* is unsafe if the platform can reorder a memory access (either load or
* store) after a following store; platforms where this is possible must
* define their own S_UNLOCK. But CPU reordering is not the only concern:
* if we simply defined S_UNLOCK() as an inline macro, the compiler might
* reorder instructions from inside the critical section to occur after the
* lock release. Since the compiler probably can't know what the external
* function s_unlock is doing, putting the same logic there should be adequate.
* A sufficiently-smart globally optimizing compiler could break that
* assumption, though, and the cost of a function call for every spinlock
* release may hurt performance significantly, so we use this implementation
* only for platforms where we don't know of a suitable intrinsic. For the
* most part, those are relatively obscure platform/compiler combinations to
* which the PostgreSQL project does not have access.
*/
#define USE_DEFAULT_S_UNLOCK
extern void s_unlock(volatile slock_t *lock);
#define S_UNLOCK(lock) s_unlock(lock)
#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 */
#if !defined(TAS_SPIN)
#define TAS_SPIN(lock) TAS(lock)
#endif /* TAS_SPIN */
/*
* Platform-independent out-of-line support routines
*/
extern int s_lock(volatile slock_t *lock, const char *file, int line, const char *func);
/* Support for dynamic adjustment of spins_per_delay */
#define DEFAULT_SPINS_PER_DELAY 100
extern void set_spins_per_delay(int shared_spins_per_delay);
extern int update_spins_per_delay(int shared_spins_per_delay);
/*
* Support for spin delay which is useful in various places where
* spinlock-like procedures take place.
*/
typedef struct
{
int spins;
int delays;
int cur_delay;
const char *file;
int line;
const char *func;
} SpinDelayStatus;
static inline void
init_spin_delay(SpinDelayStatus *status,
const char *file, int line, const char *func)
{
status->spins = 0;
status->delays = 0;
status->cur_delay = 0;
status->file = file;
status->line = line;
status->func = func;
}
#define init_local_spin_delay(status) init_spin_delay(status, __FILE__, __LINE__, __func__)
extern void perform_spin_delay(SpinDelayStatus *status);
extern void finish_spin_delay(SpinDelayStatus *status);
#endif /* S_LOCK_H */
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