Coverage Report

Created: 2021-01-23 06:44

/Users/buildslave/jenkins/workspace/coverage/llvm-project/libcxx/src/atomic.cpp
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//===------------------------- atomic.cpp ---------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include <__config>
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#ifndef _LIBCPP_HAS_NO_THREADS
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#include <climits>
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#include <atomic>
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#include <functional>
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#ifdef __linux__
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#include <unistd.h>
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#include <linux/futex.h>
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#include <sys/syscall.h>
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#else // <- Add other operating systems here
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// Baseline needs no new headers
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#endif
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_LIBCPP_BEGIN_NAMESPACE_STD
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#ifdef __linux__
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static void __libcpp_platform_wait_on_address(__cxx_atomic_contention_t const volatile* __ptr,
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                                              __cxx_contention_t __val)
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{
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    static constexpr timespec __timeout = { 2, 0 };
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    syscall(SYS_futex, __ptr, FUTEX_WAIT_PRIVATE, __val, &__timeout, 0, 0);
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}
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static void __libcpp_platform_wake_by_address(__cxx_atomic_contention_t const volatile* __ptr,
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                                              bool __notify_one)
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{
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    syscall(SYS_futex, __ptr, FUTEX_WAKE_PRIVATE, __notify_one ? 1 : INT_MAX, 0, 0, 0);
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}
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#elif defined(__APPLE__) && defined(_LIBCPP_USE_ULOCK)
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extern "C" int __ulock_wait(uint32_t operation, void *addr, uint64_t value,
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    uint32_t timeout); /* timeout is specified in microseconds */
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extern "C" int __ulock_wake(uint32_t operation, void *addr, uint64_t wake_value);
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#define UL_COMPARE_AND_WAIT       1
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#define ULF_WAKE_ALL          0x00000100
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static void __libcpp_platform_wait_on_address(__cxx_atomic_contention_t const volatile* __ptr,
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                                              __cxx_contention_t __val)
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{
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    __ulock_wait(UL_COMPARE_AND_WAIT,
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                 const_cast<__cxx_atomic_contention_t*>(__ptr), __val, 0);
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}
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static void __libcpp_platform_wake_by_address(__cxx_atomic_contention_t const volatile* __ptr,
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                                              bool __notify_one)
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{
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    __ulock_wake(UL_COMPARE_AND_WAIT | (__notify_one ? 0 : ULF_WAKE_ALL),
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                 const_cast<__cxx_atomic_contention_t*>(__ptr), 0);
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}
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#else // <- Add other operating systems here
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// Baseline is just a timed backoff
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static void __libcpp_platform_wait_on_address(__cxx_atomic_contention_t const volatile* __ptr,
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                                              __cxx_contention_t __val)
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{
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    __libcpp_thread_poll_with_backoff([=]() -> bool {
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        return !__cxx_nonatomic_compare_equal(__cxx_atomic_load(__ptr, memory_order_relaxed), __val);
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    }, __libcpp_timed_backoff_policy());
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}
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static void __libcpp_platform_wake_by_address(__cxx_atomic_contention_t const volatile*, bool) { }
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#endif // __linux__
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static constexpr size_t __libcpp_contention_table_size = (1 << 8);  /* < there's no magic in this number */
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struct alignas(64) /*  aim to avoid false sharing */ __libcpp_contention_table_entry
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{
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    __cxx_atomic_contention_t __contention_state;
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    __cxx_atomic_contention_t __platform_state;
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    inline constexpr __libcpp_contention_table_entry() :
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        __contention_state(0), __platform_state(0) { }
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};
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static __libcpp_contention_table_entry __libcpp_contention_table[ __libcpp_contention_table_size ];
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static hash<void const volatile*> __libcpp_contention_hasher;
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static __libcpp_contention_table_entry* __libcpp_contention_state(void const volatile * p)
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{
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    return &__libcpp_contention_table[__libcpp_contention_hasher(p) & (__libcpp_contention_table_size - 1)];
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}
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/* Given an atomic to track contention and an atomic to actually wait on, which may be
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   the same atomic, we try to detect contention to avoid spuriously calling the platform. */
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static void __libcpp_contention_notify(__cxx_atomic_contention_t volatile* __contention_state,
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                                       __cxx_atomic_contention_t const volatile* __platform_state,
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                                       bool __notify_one)
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{
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    if(0 != __cxx_atomic_load(__contention_state, memory_order_seq_cst))
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        // We only call 'wake' if we consumed a contention bit here.
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        __libcpp_platform_wake_by_address(__platform_state, __notify_one);
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}
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static __cxx_contention_t __libcpp_contention_monitor_for_wait(__cxx_atomic_contention_t volatile* __contention_state,
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                                                               __cxx_atomic_contention_t const volatile* __platform_state)
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{
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    // We will monitor this value.
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    return __cxx_atomic_load(__platform_state, memory_order_acquire);
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}
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static void __libcpp_contention_wait(__cxx_atomic_contention_t volatile* __contention_state,
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                                     __cxx_atomic_contention_t const volatile* __platform_state,
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                                     __cxx_contention_t __old_value)
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{
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    __cxx_atomic_fetch_add(__contention_state, __cxx_contention_t(1), memory_order_seq_cst);
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    // We sleep as long as the monitored value hasn't changed.
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    __libcpp_platform_wait_on_address(__platform_state, __old_value);
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    __cxx_atomic_fetch_sub(__contention_state, __cxx_contention_t(1), memory_order_release);
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}
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/* When the incoming atomic is the wrong size for the platform wait size, need to
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   launder the value sequence through an atomic from our table. */
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static void __libcpp_atomic_notify(void const volatile* __location)
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{
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    auto const __entry = __libcpp_contention_state(__location);
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    // The value sequence laundering happens on the next line below.
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    __cxx_atomic_fetch_add(&__entry->__platform_state, __cxx_contention_t(1), memory_order_release);
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    __libcpp_contention_notify(&__entry->__contention_state,
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                               &__entry->__platform_state,
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                               false /* when laundering, we can't handle notify_one */);
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}
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_LIBCPP_EXPORTED_FROM_ABI
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void __cxx_atomic_notify_one(void const volatile* __location)
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    { __libcpp_atomic_notify(__location); }
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_LIBCPP_EXPORTED_FROM_ABI
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void __cxx_atomic_notify_all(void const volatile* __location)
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    { __libcpp_atomic_notify(__location); }
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_LIBCPP_EXPORTED_FROM_ABI
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__cxx_contention_t __libcpp_atomic_monitor(void const volatile* __location)
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{
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    auto const __entry = __libcpp_contention_state(__location);
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    return __libcpp_contention_monitor_for_wait(&__entry->__contention_state, &__entry->__platform_state);
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}
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_LIBCPP_EXPORTED_FROM_ABI
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void __libcpp_atomic_wait(void const volatile* __location, __cxx_contention_t __old_value)
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{
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    auto const __entry = __libcpp_contention_state(__location);
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    __libcpp_contention_wait(&__entry->__contention_state, &__entry->__platform_state, __old_value);
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}
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/* When the incoming atomic happens to be the platform wait size, we still need to use the
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   table for the contention detection, but we can use the atomic directly for the wait. */
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_LIBCPP_EXPORTED_FROM_ABI
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void __cxx_atomic_notify_one(__cxx_atomic_contention_t const volatile* __location)
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{
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    __libcpp_contention_notify(&__libcpp_contention_state(__location)->__contention_state, __location, true);
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}
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_LIBCPP_EXPORTED_FROM_ABI
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void __cxx_atomic_notify_all(__cxx_atomic_contention_t const volatile* __location)
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{
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    __libcpp_contention_notify(&__libcpp_contention_state(__location)->__contention_state, __location, false);
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}
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_LIBCPP_EXPORTED_FROM_ABI
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__cxx_contention_t __libcpp_atomic_monitor(__cxx_atomic_contention_t const volatile* __location)
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{
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    return __libcpp_contention_monitor_for_wait(&__libcpp_contention_state(__location)->__contention_state, __location);
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}
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_LIBCPP_EXPORTED_FROM_ABI
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void __libcpp_atomic_wait(__cxx_atomic_contention_t const volatile* __location, __cxx_contention_t __old_value)
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{
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    __libcpp_contention_wait(&__libcpp_contention_state(__location)->__contention_state, __location, __old_value);
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}
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_LIBCPP_END_NAMESPACE_STD
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#endif //_LIBCPP_HAS_NO_THREADS