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/*-------------------------------------------------------------------------
*
* fallback.h
* Fallback for platforms without spinlock and/or atomics support. Slower
* than native atomics support, but not unusably slow.
*
* Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/port/atomics/fallback.h
*
*-------------------------------------------------------------------------
*/
/* intentionally no include guards, should only be included by atomics.h */
#ifndef INSIDE_ATOMICS_H
# error "should be included via atomics.h"
#endif
#ifndef pg_memory_barrier_impl
/*
* If we have no memory barrier implementation for this architecture, we
* fall back to acquiring and releasing a spinlock. This might, in turn,
* fall back to the semaphore-based spinlock implementation, which will be
* amazingly slow.
*
* It's not self-evident that every possible legal implementation of a
* spinlock acquire-and-release would be equivalent to a full memory barrier.
* For example, I'm not sure that Itanium's acq and rel add up to a full
* fence. But all of our actual implementations seem OK in this regard.
*/
#define PG_HAVE_MEMORY_BARRIER_EMULATION
extern void pg_spinlock_barrier(void);
#define pg_memory_barrier_impl pg_spinlock_barrier
#endif
#ifndef pg_compiler_barrier_impl
/*
* If the compiler/arch combination does not provide compiler barriers,
* provide a fallback. The fallback simply consists of a function call into
* an externally defined function. That should guarantee compiler barrier
* semantics except for compilers that do inter translation unit/global
* optimization - those better provide an actual compiler barrier.
*
* A native compiler barrier for sure is a lot faster than this...
*/
#define PG_HAVE_COMPILER_BARRIER_EMULATION
extern void pg_extern_compiler_barrier(void);
#define pg_compiler_barrier_impl pg_extern_compiler_barrier
#endif
/*
* If we have atomics implementation for this platform, fall back to providing
* the atomics API using a spinlock to protect the internal state. Possibly
* the spinlock implementation uses semaphores internally...
*
* We have to be a bit careful here, as it's not guaranteed that atomic
* variables are mapped to the same address in every process (e.g. dynamic
* shared memory segments). We can't just hash the address and use that to map
* to a spinlock. Instead assign a spinlock on initialization of the atomic
* variable.
*/
#if !defined(PG_HAVE_ATOMIC_FLAG_SUPPORT) && !defined(PG_HAVE_ATOMIC_U32_SUPPORT)
#define PG_HAVE_ATOMIC_FLAG_SIMULATION
#define PG_HAVE_ATOMIC_FLAG_SUPPORT
typedef struct pg_atomic_flag
{
/*
* To avoid circular includes we can't use s_lock as a type here. Instead
* just reserve enough space for all spinlock types. Some platforms would
* be content with just one byte instead of 4, but that's not too much
* waste.
*/
#if defined(__hppa) || defined(__hppa__) /* HP PA-RISC, GCC and HP compilers */
int sema[4];
#else
int sema;
#endif
volatile bool value;
} pg_atomic_flag;
#endif /* PG_HAVE_ATOMIC_FLAG_SUPPORT */
#if !defined(PG_HAVE_ATOMIC_U32_SUPPORT)
#define PG_HAVE_ATOMIC_U32_SIMULATION
#define PG_HAVE_ATOMIC_U32_SUPPORT
typedef struct pg_atomic_uint32
{
/* Check pg_atomic_flag's definition above for an explanation */
#if defined(__hppa) || defined(__hppa__) /* HP PA-RISC, GCC and HP compilers */
int sema[4];
#else
int sema;
#endif
volatile uint32 value;
} pg_atomic_uint32;
#endif /* PG_HAVE_ATOMIC_U32_SUPPORT */
#if !defined(PG_HAVE_ATOMIC_U64_SUPPORT)
#define PG_HAVE_ATOMIC_U64_SIMULATION
#define PG_HAVE_ATOMIC_U64_SUPPORT
typedef struct pg_atomic_uint64
{
/* Check pg_atomic_flag's definition above for an explanation */
#if defined(__hppa) || defined(__hppa__) /* HP PA-RISC, GCC and HP compilers */
int sema[4];
#else
int sema;
#endif
volatile uint64 value;
} pg_atomic_uint64;
#endif /* PG_HAVE_ATOMIC_U64_SUPPORT */
#ifdef PG_HAVE_ATOMIC_FLAG_SIMULATION
#define PG_HAVE_ATOMIC_INIT_FLAG
extern void pg_atomic_init_flag_impl(volatile pg_atomic_flag *ptr);
#define PG_HAVE_ATOMIC_TEST_SET_FLAG
extern bool pg_atomic_test_set_flag_impl(volatile pg_atomic_flag *ptr);
#define PG_HAVE_ATOMIC_CLEAR_FLAG
extern void pg_atomic_clear_flag_impl(volatile pg_atomic_flag *ptr);
#define PG_HAVE_ATOMIC_UNLOCKED_TEST_FLAG
extern bool pg_atomic_unlocked_test_flag_impl(volatile pg_atomic_flag *ptr);
#endif /* PG_HAVE_ATOMIC_FLAG_SIMULATION */
#ifdef PG_HAVE_ATOMIC_U32_SIMULATION
#define PG_HAVE_ATOMIC_INIT_U32
extern void pg_atomic_init_u32_impl(volatile pg_atomic_uint32 *ptr, uint32 val_);
#define PG_HAVE_ATOMIC_WRITE_U32
extern void pg_atomic_write_u32_impl(volatile pg_atomic_uint32 *ptr, uint32 val);
#define PG_HAVE_ATOMIC_COMPARE_EXCHANGE_U32
extern bool pg_atomic_compare_exchange_u32_impl(volatile pg_atomic_uint32 *ptr,
uint32 *expected, uint32 newval);
#define PG_HAVE_ATOMIC_FETCH_ADD_U32
extern uint32 pg_atomic_fetch_add_u32_impl(volatile pg_atomic_uint32 *ptr, int32 add_);
#endif /* PG_HAVE_ATOMIC_U32_SIMULATION */
#ifdef PG_HAVE_ATOMIC_U64_SIMULATION
#define PG_HAVE_ATOMIC_INIT_U64
extern void pg_atomic_init_u64_impl(volatile pg_atomic_uint64 *ptr, uint64 val_);
#define PG_HAVE_ATOMIC_COMPARE_EXCHANGE_U64
extern bool pg_atomic_compare_exchange_u64_impl(volatile pg_atomic_uint64 *ptr,
uint64 *expected, uint64 newval);
#define PG_HAVE_ATOMIC_FETCH_ADD_U64
extern uint64 pg_atomic_fetch_add_u64_impl(volatile pg_atomic_uint64 *ptr, int64 add_);
#endif /* PG_HAVE_ATOMIC_U64_SIMULATION */
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