5e7605fad2
The idle thread is now actually run when the system is idle because it truly goes idle. The idle thread is made power efficient by using the hlt instruction rather than a busy loop. The new futex(2) system call is used to implement fast user-space mutexes, condition variables, and semaphores. The same backend and design is used as kutexes for truly sleeping kernel mutexes and condition variables. The new exit_thread(2) flag EXIT_THREAD_FUTEX_WAKE wakes a futex. Sleeping on clocks in the kernel now uses timers for true sleep. The interrupt worker thread now truly sleeps when idle. Kernel threads are now named. This is a compatible ABI change.
35 lines
1.2 KiB
C
35 lines
1.2 KiB
C
/*
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* Copyright (c) 2014, 2021 Jonas 'Sortie' Termansen.
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*
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* semaphore/sem_trywait.c
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* Try to lock a semaphore.
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*/
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#include <errno.h>
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#include <semaphore.h>
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#include <stdbool.h>
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int sem_trywait(sem_t* sem)
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{
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int old = __atomic_load_n(&sem->value, __ATOMIC_SEQ_CST);
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if ( old <= 0 )
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return errno = EAGAIN, -1;
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int new = old != -1 ? old - 1 : -1;
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if ( !__atomic_compare_exchange_n(&sem->value, &old, new, false,
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__ATOMIC_SEQ_CST, __ATOMIC_RELAXED) )
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return errno = EAGAIN, -1;
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return 0;
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}
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