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//===-- sanitizer_lfstack.h -=-----------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Lock-free stack.
// Uses 32/17 bits as ABA-counter on 32/64-bit platforms.
// The memory passed to Push() must not be ever munmap'ed.
// The type T must contain T *next field.
//
//===----------------------------------------------------------------------===//
#ifndef SANITIZER_LFSTACK_H
#define SANITIZER_LFSTACK_H
#include "sanitizer_internal_defs.h"
#include "sanitizer_common.h"
#include "sanitizer_atomic.h"
namespace __sanitizer {
template<typename T>
struct LFStack {
void Clear() {
atomic_store(&head_, 0, memory_order_relaxed);
}
bool Empty() const {
return (atomic_load(&head_, memory_order_relaxed) & kPtrMask) == 0;
}
void Push(T *p) {
u64 cmp = atomic_load(&head_, memory_order_relaxed);
for (;;) {
u64 cnt = (cmp & kCounterMask) + kCounterInc;
u64 xch = (u64)(uptr)p | cnt;
p->next = (T*)(uptr)(cmp & kPtrMask);
if (atomic_compare_exchange_weak(&head_, &cmp, xch,
memory_order_release))
break;
}
}
T *Pop() {
u64 cmp = atomic_load(&head_, memory_order_acquire);
for (;;) {
T *cur = (T*)(uptr)(cmp & kPtrMask);
if (!cur)
return nullptr;
T *nxt = cur->next;
u64 cnt = (cmp & kCounterMask);
u64 xch = (u64)(uptr)nxt | cnt;
if (atomic_compare_exchange_weak(&head_, &cmp, xch,
memory_order_acquire))
return cur;
}
}
// private:
static const int kCounterBits = FIRST_32_SECOND_64(32, 17);
static const u64 kPtrMask = ((u64)-1) >> kCounterBits;
static const u64 kCounterMask = ~kPtrMask;
static const u64 kCounterInc = kPtrMask + 1;
atomic_uint64_t head_;
};
} // namespace __sanitizer
#endif // SANITIZER_LFSTACK_H
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