789c7f1b6c
- Prefer Sleep(1) over sched_yield() for pre-Vista thread yield.
On Windows sched_yield is often implemented as Sleep(0) which only
yields to threads of highest priority to current priority. However,
during libcurl initialization if there is thread contention then it's
possible that there is a wait for a different library or OS thread of
a lesser priority and then the yield is not effective during that time.
On the other hand Sleep(1) will wait the minimum time slice which is
usually like 15ms or more.
Prior to this change 2c4bfef removed sched_yield detection on Windows,
which effectively removed the yield in the spin lock, and therefore this
change restores the yield but in a different way.
For Windows Vista and later we use SRW locks and do not have this issue.
Ref: https://github.com/curl/curl/pull/16037#issuecomment-2600161764
Ref: https://devblogs.microsoft.com/oldnewthing/20051004-09/?p=33923
Closes https://github.com/curl/curl/pull/16048
114 lines
3.2 KiB
C
114 lines
3.2 KiB
C
#ifndef HEADER_CURL_EASY_LOCK_H
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#define HEADER_CURL_EASY_LOCK_H
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/***************************************************************************
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* _ _ ____ _
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* Project ___| | | | _ \| |
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* / __| | | | |_) | |
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* | (__| |_| | _ <| |___
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* \___|\___/|_| \_\_____|
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*
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* Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
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*
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* This software is licensed as described in the file COPYING, which
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* you should have received as part of this distribution. The terms
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* are also available at https://curl.se/docs/copyright.html.
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*
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* You may opt to use, copy, modify, merge, publish, distribute and/or sell
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* copies of the Software, and permit persons to whom the Software is
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* furnished to do so, under the terms of the COPYING file.
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*
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* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
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* KIND, either express or implied.
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*
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* SPDX-License-Identifier: curl
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*
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***************************************************************************/
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#include "curl_setup.h"
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#define GLOBAL_INIT_IS_THREADSAFE
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#if defined(_WIN32_WINNT) && _WIN32_WINNT >= 0x600
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#ifdef __MINGW32__
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#ifndef SRWLOCK_INIT
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#define SRWLOCK_INIT NULL
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#endif
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#endif /* __MINGW32__ */
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#define curl_simple_lock SRWLOCK
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#define CURL_SIMPLE_LOCK_INIT SRWLOCK_INIT
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#define curl_simple_lock_lock(m) AcquireSRWLockExclusive(m)
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#define curl_simple_lock_unlock(m) ReleaseSRWLockExclusive(m)
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#elif defined(HAVE_ATOMIC) && defined(HAVE_STDATOMIC_H)
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#include <stdatomic.h>
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#if defined(HAVE_SCHED_YIELD)
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#include <sched.h>
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#endif
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#define curl_simple_lock atomic_int
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#define CURL_SIMPLE_LOCK_INIT 0
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/* a clang-thing */
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#ifndef __has_builtin
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#define __has_builtin(x) 0
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#endif
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#ifndef __INTEL_COMPILER
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/* The Intel compiler tries to look like GCC *and* clang *and* lies in its
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__has_builtin() function, so override it. */
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/* if GCC on i386/x86_64 or if the built-in is present */
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#if ( (defined(__GNUC__) && !defined(__clang__)) && \
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(defined(__i386__) || defined(__x86_64__))) || \
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__has_builtin(__builtin_ia32_pause)
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#define HAVE_BUILTIN_IA32_PAUSE
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#endif
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#endif
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static CURL_INLINE void curl_simple_lock_lock(curl_simple_lock *lock)
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{
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for(;;) {
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if(!atomic_exchange_explicit(lock, true, memory_order_acquire))
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break;
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/* Reduce cache coherency traffic */
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while(atomic_load_explicit(lock, memory_order_relaxed)) {
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/* Reduce load (not mandatory) */
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#ifdef HAVE_BUILTIN_IA32_PAUSE
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__builtin_ia32_pause();
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#elif defined(__aarch64__)
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__asm__ volatile("yield" ::: "memory");
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#elif defined(_WIN32)
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Sleep(1);
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#elif defined(HAVE_SCHED_YIELD)
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sched_yield();
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#endif
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}
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}
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}
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static CURL_INLINE void curl_simple_lock_unlock(curl_simple_lock *lock)
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{
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atomic_store_explicit(lock, false, memory_order_release);
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}
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#elif defined(USE_THREADS_POSIX) && defined(HAVE_PTHREAD_H)
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#include <pthread.h>
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#define curl_simple_lock pthread_mutex_t
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#define CURL_SIMPLE_LOCK_INIT PTHREAD_MUTEX_INITIALIZER
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#define curl_simple_lock_lock(m) pthread_mutex_lock(m)
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#define curl_simple_lock_unlock(m) pthread_mutex_unlock(m)
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#else
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#undef GLOBAL_INIT_IS_THREADSAFE
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#endif
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#endif /* HEADER_CURL_EASY_LOCK_H */
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