forked from OSchip/llvm-project
339 lines
11 KiB
C
339 lines
11 KiB
C
/*===-- atomic.c - Implement support functions for atomic operations.------===
|
|
*
|
|
* The LLVM Compiler Infrastructure
|
|
*
|
|
* This file is dual licensed under the MIT and the University of Illinois Open
|
|
* Source Licenses. See LICENSE.TXT for details.
|
|
*
|
|
*===----------------------------------------------------------------------===
|
|
*
|
|
* atomic.c defines a set of functions for performing atomic accesses on
|
|
* arbitrary-sized memory locations. This design uses locks that should
|
|
* be fast in the uncontended case, for two reasons:
|
|
*
|
|
* 1) This code must work with C programs that do not link to anything
|
|
* (including pthreads) and so it should not depend on any pthread
|
|
* functions.
|
|
* 2) Atomic operations, rather than explicit mutexes, are most commonly used
|
|
* on code where contended operations are rate.
|
|
*
|
|
* To avoid needing a per-object lock, this code allocates an array of
|
|
* locks and hashes the object pointers to find the one that it should use.
|
|
* For operations that must be atomic on two locations, the lower lock is
|
|
* always acquired first, to avoid deadlock.
|
|
*
|
|
*===----------------------------------------------------------------------===
|
|
*/
|
|
|
|
#include <stdint.h>
|
|
#include <string.h>
|
|
|
|
#include "assembly.h"
|
|
|
|
// Clang objects if you redefine a builtin. This little hack allows us to
|
|
// define a function with the same name as an intrinsic.
|
|
#pragma redefine_extname __atomic_load_c SYMBOL_NAME(__atomic_load)
|
|
#pragma redefine_extname __atomic_store_c SYMBOL_NAME(__atomic_store)
|
|
#pragma redefine_extname __atomic_exchange_c SYMBOL_NAME(__atomic_exchange)
|
|
#pragma redefine_extname __atomic_compare_exchange_c SYMBOL_NAME(__atomic_compare_exchange)
|
|
|
|
/// Number of locks. This allocates one page on 32-bit platforms, two on
|
|
/// 64-bit. This can be specified externally if a different trade between
|
|
/// memory usage and contention probability is required for a given platform.
|
|
#ifndef SPINLOCK_COUNT
|
|
#define SPINLOCK_COUNT (1<<10)
|
|
#endif
|
|
static const long SPINLOCK_MASK = SPINLOCK_COUNT - 1;
|
|
|
|
////////////////////////////////////////////////////////////////////////////////
|
|
// Platform-specific lock implementation. Falls back to spinlocks if none is
|
|
// defined. Each platform should define the Lock type, and corresponding
|
|
// lock() and unlock() functions.
|
|
////////////////////////////////////////////////////////////////////////////////
|
|
#ifdef __FreeBSD__
|
|
#include <errno.h>
|
|
#include <sys/types.h>
|
|
#include <machine/atomic.h>
|
|
#include <sys/umtx.h>
|
|
typedef struct _usem Lock;
|
|
__inline static void unlock(Lock *l) {
|
|
__c11_atomic_store((_Atomic(uint32_t)*)&l->_count, 1, __ATOMIC_RELEASE);
|
|
__c11_atomic_thread_fence(__ATOMIC_SEQ_CST);
|
|
if (l->_has_waiters)
|
|
_umtx_op(l, UMTX_OP_SEM_WAKE, 1, 0, 0);
|
|
}
|
|
__inline static void lock(Lock *l) {
|
|
uint32_t old = 1;
|
|
while (!__c11_atomic_compare_exchange_weak((_Atomic(uint32_t)*)&l->_count, &old,
|
|
0, __ATOMIC_ACQUIRE, __ATOMIC_RELAXED)) {
|
|
_umtx_op(l, UMTX_OP_SEM_WAIT, 0, 0, 0);
|
|
old = 1;
|
|
}
|
|
}
|
|
/// locks for atomic operations
|
|
static Lock locks[SPINLOCK_COUNT] = { [0 ... SPINLOCK_COUNT-1] = {0,1,0} };
|
|
|
|
#elif defined(__APPLE__)
|
|
#include <libkern/OSAtomic.h>
|
|
typedef OSSpinLock Lock;
|
|
__inline static void unlock(Lock *l) {
|
|
OSSpinLockUnlock(l);
|
|
}
|
|
/// Locks a lock. In the current implementation, this is potentially
|
|
/// unbounded in the contended case.
|
|
__inline static void lock(Lock *l) {
|
|
OSSpinLockLock(l);
|
|
}
|
|
static Lock locks[SPINLOCK_COUNT]; // initialized to OS_SPINLOCK_INIT which is 0
|
|
|
|
#else
|
|
typedef _Atomic(uintptr_t) Lock;
|
|
/// Unlock a lock. This is a release operation.
|
|
__inline static void unlock(Lock *l) {
|
|
__c11_atomic_store(l, 0, __ATOMIC_RELEASE);
|
|
}
|
|
/// Locks a lock. In the current implementation, this is potentially
|
|
/// unbounded in the contended case.
|
|
__inline static void lock(Lock *l) {
|
|
uintptr_t old = 0;
|
|
while (!__c11_atomic_compare_exchange_weak(l, &old, 1, __ATOMIC_ACQUIRE,
|
|
__ATOMIC_RELAXED))
|
|
old = 0;
|
|
}
|
|
/// locks for atomic operations
|
|
static Lock locks[SPINLOCK_COUNT];
|
|
#endif
|
|
|
|
|
|
/// Returns a lock to use for a given pointer.
|
|
static __inline Lock *lock_for_pointer(void *ptr) {
|
|
intptr_t hash = (intptr_t)ptr;
|
|
// Disregard the lowest 4 bits. We want all values that may be part of the
|
|
// same memory operation to hash to the same value and therefore use the same
|
|
// lock.
|
|
hash >>= 4;
|
|
// Use the next bits as the basis for the hash
|
|
intptr_t low = hash & SPINLOCK_MASK;
|
|
// Now use the high(er) set of bits to perturb the hash, so that we don't
|
|
// get collisions from atomic fields in a single object
|
|
hash >>= 16;
|
|
hash ^= low;
|
|
// Return a pointer to the word to use
|
|
return locks + (hash & SPINLOCK_MASK);
|
|
}
|
|
|
|
/// Macros for determining whether a size is lock free. Clang can not yet
|
|
/// codegen __atomic_is_lock_free(16), so for now we assume 16-byte values are
|
|
/// not lock free.
|
|
#define IS_LOCK_FREE_1 __c11_atomic_is_lock_free(1)
|
|
#define IS_LOCK_FREE_2 __c11_atomic_is_lock_free(2)
|
|
#define IS_LOCK_FREE_4 __c11_atomic_is_lock_free(4)
|
|
#define IS_LOCK_FREE_8 __c11_atomic_is_lock_free(8)
|
|
#define IS_LOCK_FREE_16 0
|
|
|
|
/// Macro that calls the compiler-generated lock-free versions of functions
|
|
/// when they exist.
|
|
#define LOCK_FREE_CASES() \
|
|
do {\
|
|
switch (size) {\
|
|
case 2:\
|
|
if (IS_LOCK_FREE_2) {\
|
|
LOCK_FREE_ACTION(uint16_t);\
|
|
}\
|
|
case 4:\
|
|
if (IS_LOCK_FREE_4) {\
|
|
LOCK_FREE_ACTION(uint32_t);\
|
|
}\
|
|
case 8:\
|
|
if (IS_LOCK_FREE_8) {\
|
|
LOCK_FREE_ACTION(uint64_t);\
|
|
}\
|
|
case 16:\
|
|
if (IS_LOCK_FREE_16) {\
|
|
/* FIXME: __uint128_t isn't available on 32 bit platforms.
|
|
LOCK_FREE_ACTION(__uint128_t);*/\
|
|
}\
|
|
}\
|
|
} while (0)
|
|
|
|
|
|
/// An atomic load operation. This is atomic with respect to the source
|
|
/// pointer only.
|
|
void __atomic_load_c(int size, void *src, void *dest, int model) {
|
|
#define LOCK_FREE_ACTION(type) \
|
|
*((type*)dest) = __c11_atomic_load((_Atomic(type)*)src, model);\
|
|
return;
|
|
LOCK_FREE_CASES();
|
|
#undef LOCK_FREE_ACTION
|
|
Lock *l = lock_for_pointer(src);
|
|
lock(l);
|
|
memcpy(dest, src, size);
|
|
unlock(l);
|
|
}
|
|
|
|
/// An atomic store operation. This is atomic with respect to the destination
|
|
/// pointer only.
|
|
void __atomic_store_c(int size, void *dest, void *src, int model) {
|
|
#define LOCK_FREE_ACTION(type) \
|
|
__c11_atomic_store((_Atomic(type)*)dest, *(type*)dest, model);\
|
|
return;
|
|
LOCK_FREE_CASES();
|
|
#undef LOCK_FREE_ACTION
|
|
Lock *l = lock_for_pointer(dest);
|
|
lock(l);
|
|
memcpy(dest, src, size);
|
|
unlock(l);
|
|
}
|
|
|
|
/// Atomic compare and exchange operation. If the value at *ptr is identical
|
|
/// to the value at *expected, then this copies value at *desired to *ptr. If
|
|
/// they are not, then this stores the current value from *ptr in *expected.
|
|
///
|
|
/// This function returns 1 if the exchange takes place or 0 if it fails.
|
|
int __atomic_compare_exchange_c(int size, void *ptr, void *expected,
|
|
void *desired, int success, int failure) {
|
|
#define LOCK_FREE_ACTION(type) \
|
|
return __c11_atomic_compare_exchange_strong((_Atomic(type)*)ptr, (type*)expected,\
|
|
*(type*)desired, success, failure)
|
|
LOCK_FREE_CASES();
|
|
#undef LOCK_FREE_ACTION
|
|
Lock *l = lock_for_pointer(ptr);
|
|
lock(l);
|
|
if (memcmp(ptr, expected, size) == 0) {
|
|
memcpy(ptr, desired, size);
|
|
unlock(l);
|
|
return 1;
|
|
}
|
|
memcpy(expected, ptr, size);
|
|
unlock(l);
|
|
return 0;
|
|
}
|
|
|
|
/// Performs an atomic exchange operation between two pointers. This is atomic
|
|
/// with respect to the target address.
|
|
void __atomic_exchange_c(int size, void *ptr, void *val, void *old, int model) {
|
|
#define LOCK_FREE_ACTION(type) \
|
|
*(type*)old = __c11_atomic_exchange((_Atomic(type)*)ptr, *(type*)val,\
|
|
model);\
|
|
return;
|
|
LOCK_FREE_CASES();
|
|
#undef LOCK_FREE_ACTION
|
|
Lock *l = lock_for_pointer(ptr);
|
|
lock(l);
|
|
memcpy(old, ptr, size);
|
|
memcpy(ptr, val, size);
|
|
unlock(l);
|
|
}
|
|
|
|
////////////////////////////////////////////////////////////////////////////////
|
|
// Where the size is known at compile time, the compiler may emit calls to
|
|
// specialised versions of the above functions.
|
|
////////////////////////////////////////////////////////////////////////////////
|
|
#ifdef __SIZEOF_INT128__
|
|
#define OPTIMISED_CASES\
|
|
OPTIMISED_CASE(1, IS_LOCK_FREE_1, uint8_t)\
|
|
OPTIMISED_CASE(2, IS_LOCK_FREE_2, uint16_t)\
|
|
OPTIMISED_CASE(4, IS_LOCK_FREE_4, uint32_t)\
|
|
OPTIMISED_CASE(8, IS_LOCK_FREE_8, uint64_t)\
|
|
OPTIMISED_CASE(16, IS_LOCK_FREE_16, __uint128_t)
|
|
#else
|
|
#define OPTIMISED_CASES\
|
|
OPTIMISED_CASE(1, IS_LOCK_FREE_1, uint8_t)\
|
|
OPTIMISED_CASE(2, IS_LOCK_FREE_2, uint16_t)\
|
|
OPTIMISED_CASE(4, IS_LOCK_FREE_4, uint32_t)\
|
|
OPTIMISED_CASE(8, IS_LOCK_FREE_8, uint64_t)
|
|
#endif
|
|
|
|
#define OPTIMISED_CASE(n, lockfree, type)\
|
|
type __atomic_load_##n(type *src, int model) {\
|
|
if (lockfree)\
|
|
return __c11_atomic_load((_Atomic(type)*)src, model);\
|
|
Lock *l = lock_for_pointer(src);\
|
|
lock(l);\
|
|
type val = *src;\
|
|
unlock(l);\
|
|
return val;\
|
|
}
|
|
OPTIMISED_CASES
|
|
#undef OPTIMISED_CASE
|
|
|
|
#define OPTIMISED_CASE(n, lockfree, type)\
|
|
void __atomic_store_##n(type *dest, type val, int model) {\
|
|
if (lockfree) {\
|
|
__c11_atomic_store((_Atomic(type)*)dest, val, model);\
|
|
return;\
|
|
}\
|
|
Lock *l = lock_for_pointer(dest);\
|
|
lock(l);\
|
|
*dest = val;\
|
|
unlock(l);\
|
|
return;\
|
|
}
|
|
OPTIMISED_CASES
|
|
#undef OPTIMISED_CASE
|
|
|
|
#define OPTIMISED_CASE(n, lockfree, type)\
|
|
type __atomic_exchange_##n(type *dest, type val, int model) {\
|
|
if (lockfree)\
|
|
return __c11_atomic_exchange((_Atomic(type)*)dest, val, model);\
|
|
Lock *l = lock_for_pointer(dest);\
|
|
lock(l);\
|
|
type tmp = *dest;\
|
|
*dest = val;\
|
|
unlock(l);\
|
|
return tmp;\
|
|
}
|
|
OPTIMISED_CASES
|
|
#undef OPTIMISED_CASE
|
|
|
|
#define OPTIMISED_CASE(n, lockfree, type)\
|
|
int __atomic_compare_exchange_##n(type *ptr, type *expected, type desired,\
|
|
int success, int failure) {\
|
|
if (lockfree)\
|
|
return __c11_atomic_compare_exchange_strong((_Atomic(type)*)ptr, expected, desired,\
|
|
success, failure);\
|
|
Lock *l = lock_for_pointer(ptr);\
|
|
lock(l);\
|
|
if (*ptr == *expected) {\
|
|
*ptr = desired;\
|
|
unlock(l);\
|
|
return 1;\
|
|
}\
|
|
*expected = *ptr;\
|
|
unlock(l);\
|
|
return 0;\
|
|
}
|
|
OPTIMISED_CASES
|
|
#undef OPTIMISED_CASE
|
|
|
|
////////////////////////////////////////////////////////////////////////////////
|
|
// Atomic read-modify-write operations for integers of various sizes.
|
|
////////////////////////////////////////////////////////////////////////////////
|
|
#define ATOMIC_RMW(n, lockfree, type, opname, op) \
|
|
type __atomic_fetch_##opname##_##n(type *ptr, type val, int model) {\
|
|
if (lockfree) \
|
|
return __c11_atomic_fetch_##opname((_Atomic(type)*)ptr, val, model);\
|
|
Lock *l = lock_for_pointer(ptr);\
|
|
lock(l);\
|
|
type tmp = *ptr;\
|
|
*ptr = tmp op val;\
|
|
unlock(l);\
|
|
return tmp;\
|
|
}
|
|
|
|
#define OPTIMISED_CASE(n, lockfree, type) ATOMIC_RMW(n, lockfree, type, add, +)
|
|
OPTIMISED_CASES
|
|
#undef OPTIMISED_CASE
|
|
#define OPTIMISED_CASE(n, lockfree, type) ATOMIC_RMW(n, lockfree, type, sub, -)
|
|
OPTIMISED_CASES
|
|
#undef OPTIMISED_CASE
|
|
#define OPTIMISED_CASE(n, lockfree, type) ATOMIC_RMW(n, lockfree, type, and, &)
|
|
OPTIMISED_CASES
|
|
#undef OPTIMISED_CASE
|
|
#define OPTIMISED_CASE(n, lockfree, type) ATOMIC_RMW(n, lockfree, type, or, |)
|
|
OPTIMISED_CASES
|
|
#undef OPTIMISED_CASE
|
|
#define OPTIMISED_CASE(n, lockfree, type) ATOMIC_RMW(n, lockfree, type, xor, ^)
|
|
OPTIMISED_CASES
|
|
#undef OPTIMISED_CASE
|