| 1 | /* $Id: semevent-linux.cpp 8245 2008-04-21 17:24:28Z vboxsync $ */
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| 2 | /** @file
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| 3 | * IPRT - Event Semaphore, Linux (2.6.x+).
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| 4 | */
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| 5 |
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| 6 | /*
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| 7 | * Copyright (C) 2006-2007 Sun Microsystems, Inc.
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| 8 | *
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| 9 | * This file is part of VirtualBox Open Source Edition (OSE), as
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| 10 | * available from http://www.virtualbox.org. This file is free software;
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| 11 | * you can redistribute it and/or modify it under the terms of the GNU
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| 12 | * General Public License (GPL) as published by the Free Software
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| 13 | * Foundation, in version 2 as it comes in the "COPYING" file of the
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| 14 | * VirtualBox OSE distribution. VirtualBox OSE is distributed in the
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| 15 | * hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
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| 16 | *
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| 17 | * The contents of this file may alternatively be used under the terms
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| 18 | * of the Common Development and Distribution License Version 1.0
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| 19 | * (CDDL) only, as it comes in the "COPYING.CDDL" file of the
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| 20 | * VirtualBox OSE distribution, in which case the provisions of the
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| 21 | * CDDL are applicable instead of those of the GPL.
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| 22 | *
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| 23 | * You may elect to license modified versions of this file under the
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| 24 | * terms and conditions of either the GPL or the CDDL or both.
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| 25 | *
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| 26 | * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa
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| 27 | * Clara, CA 95054 USA or visit http://www.sun.com if you need
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| 28 | * additional information or have any questions.
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| 29 | */
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| 30 |
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| 31 | /*******************************************************************************
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| 32 | * Header Files *
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| 33 | *******************************************************************************/
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| 34 | #include <iprt/semaphore.h>
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| 35 | #include <iprt/assert.h>
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| 36 | #include <iprt/alloc.h>
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| 37 | #include <iprt/asm.h>
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| 38 | #include <iprt/err.h>
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| 39 | #include "internal/magics.h"
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| 40 |
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| 41 | #include <errno.h>
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| 42 | #include <limits.h>
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| 43 | #include <pthread.h>
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| 44 | #include <unistd.h>
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| 45 | #include <sys/time.h>
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| 46 | #include <sys/syscall.h>
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| 47 | #if 0 /* With 2.6.17 futex.h has become C++ unfriendly. */
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| 48 | # include <linux/futex.h>
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| 49 | #else
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| 50 | # define FUTEX_WAIT 0
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| 51 | # define FUTEX_WAKE 1
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| 52 | #endif
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| 53 |
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| 54 |
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| 55 | /*******************************************************************************
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| 56 | * Structures and Typedefs *
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| 57 | *******************************************************************************/
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| 58 | /**
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| 59 | * Linux (single wakup) event semaphore.
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| 60 | */
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| 61 | struct RTSEMEVENTINTERNAL
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| 62 | {
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| 63 | /** Magic value. */
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| 64 | intptr_t volatile iMagic;
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| 65 | /** The futex state variable.
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| 66 | * <0 means signaled.
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| 67 | * 0 means not signaled, no waiters.
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| 68 | * >0 means not signaled, and the value gives the number of waiters.
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| 69 | */
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| 70 | int32_t volatile cWaiters;
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| 71 | };
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| 72 |
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| 73 |
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| 74 | /**
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| 75 | * Wrapper for the futex syscall.
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| 76 | */
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| 77 | static long sys_futex(int32_t volatile *uaddr, int op, int val, struct timespec *utime, int32_t *uaddr2, int val3)
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| 78 | {
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| 79 | errno = 0;
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| 80 | long rc = syscall(__NR_futex, uaddr, op, val, utime, uaddr2, val3);
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| 81 | if (rc < 0)
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| 82 | {
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| 83 | Assert(rc == -1);
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| 84 | rc = -errno;
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| 85 | }
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| 86 | return rc;
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| 87 | }
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| 88 |
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| 89 |
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| 90 |
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| 91 | RTDECL(int) RTSemEventCreate(PRTSEMEVENT pEventSem)
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| 92 | {
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| 93 | /*
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| 94 | * Allocate semaphore handle.
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| 95 | */
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| 96 | struct RTSEMEVENTINTERNAL *pThis = (struct RTSEMEVENTINTERNAL *)RTMemAlloc(sizeof(struct RTSEMEVENTINTERNAL));
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| 97 | if (pThis)
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| 98 | {
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| 99 | pThis->iMagic = RTSEMEVENT_MAGIC;
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| 100 | pThis->cWaiters = 0;
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| 101 | *pEventSem = pThis;
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| 102 | return VINF_SUCCESS;
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| 103 | }
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| 104 | return VERR_NO_MEMORY;
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| 105 | }
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| 106 |
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| 107 |
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| 108 | RTDECL(int) RTSemEventDestroy(RTSEMEVENT EventSem)
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| 109 | {
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| 110 | /*
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| 111 | * Validate input.
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| 112 | */
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| 113 | struct RTSEMEVENTINTERNAL *pThis = EventSem;
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| 114 | AssertReturn(VALID_PTR(pThis) && pThis->iMagic == RTSEMEVENT_MAGIC,
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| 115 | VERR_INVALID_HANDLE);
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| 116 |
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| 117 | /*
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| 118 | * Invalidate the semaphore and wake up anyone waiting on it.
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| 119 | */
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| 120 | ASMAtomicXchgSize(&pThis->iMagic, RTSEMEVENT_MAGIC + 1);
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| 121 | if (ASMAtomicXchgS32(&pThis->cWaiters, INT32_MIN / 2) > 0)
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| 122 | {
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| 123 | sys_futex(&pThis->cWaiters, FUTEX_WAKE, INT_MAX, NULL, NULL, 0);
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| 124 | usleep(1000);
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| 125 | }
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| 126 |
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| 127 | /*
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| 128 | * Free the semaphore memory and be gone.
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| 129 | */
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| 130 | RTMemFree(pThis);
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| 131 | return VINF_SUCCESS;
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| 132 | }
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| 133 |
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| 134 |
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| 135 | RTDECL(int) RTSemEventSignal(RTSEMEVENT EventSem)
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| 136 | {
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| 137 | /*
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| 138 | * Validate input.
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| 139 | */
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| 140 | struct RTSEMEVENTINTERNAL *pThis = EventSem;
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| 141 | AssertReturn(VALID_PTR(pThis) && pThis->iMagic == RTSEMEVENT_MAGIC,
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| 142 | VERR_INVALID_HANDLE);
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| 143 | /*
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| 144 | * Try signal it.
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| 145 | */
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| 146 | for (unsigned i = 0;; i++)
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| 147 | {
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| 148 | int32_t iCur = pThis->cWaiters;
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| 149 | if (iCur == 0)
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| 150 | {
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| 151 | if (ASMAtomicCmpXchgS32(&pThis->cWaiters, -1, 0))
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| 152 | break; /* nobody is waiting */
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| 153 | }
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| 154 | else if (iCur < 0)
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| 155 | break; /* already signaled */
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| 156 | else
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| 157 | {
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| 158 | /* somebody is waiting, try wake up one of them. */
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| 159 | long cWoken = sys_futex(&pThis->cWaiters, FUTEX_WAKE, 1, NULL, NULL, 0);
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| 160 | if (RT_LIKELY(cWoken == 1))
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| 161 | {
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| 162 | ASMAtomicDecS32(&pThis->cWaiters);
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| 163 | break;
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| 164 | }
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| 165 | AssertMsg(cWoken == 0, ("%ld\n", cWoken));
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| 166 |
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| 167 | /*
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| 168 | * This path is taken in two situations:
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| 169 | * 1) A waiting thread is returning from the sys_futex call with a
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| 170 | * non-zero return value.
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| 171 | * 2) There are two threads signaling the event at the
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| 172 | * same time and only one thread waiting.
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| 173 | *
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| 174 | * At this point we know that nobody is activly waiting on the event but
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| 175 | * at the same time, we are racing someone updating the state. The current
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| 176 | * strategy is to spin till the thread racing us is done, this is kind of
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| 177 | * brain dead and need fixing of course.
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| 178 | */
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| 179 | if (RT_UNLIKELY(i > 32))
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| 180 | {
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| 181 | if ((i % 128) == 127)
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| 182 | usleep(1000);
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| 183 | else if (!(i % 4))
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| 184 | pthread_yield();
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| 185 | else
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| 186 | AssertReleaseMsg(i < 4096, ("iCur=%#x pThis=%p\n", iCur, pThis));
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| 187 | }
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| 188 | }
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| 189 | }
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| 190 | return VINF_SUCCESS;
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| 191 | }
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| 192 |
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| 193 |
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| 194 | static int rtSemEventWait(RTSEMEVENT EventSem, unsigned cMillies, bool fAutoResume)
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| 195 | {
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| 196 | /*
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| 197 | * Validate input.
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| 198 | */
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| 199 | struct RTSEMEVENTINTERNAL *pThis = EventSem;
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| 200 | AssertReturn(VALID_PTR(pThis) && pThis->iMagic == RTSEMEVENT_MAGIC,
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| 201 | VERR_INVALID_HANDLE);
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| 202 |
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| 203 | /*
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| 204 | * Quickly check whether it's signaled.
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| 205 | */
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| 206 | if (ASMAtomicCmpXchgS32(&pThis->cWaiters, 0, -1))
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| 207 | return VINF_SUCCESS;
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| 208 |
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| 209 | /*
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| 210 | * Convert timeout value.
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| 211 | */
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| 212 | struct timespec ts;
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| 213 | struct timespec *pTimeout = NULL;
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| 214 | if (cMillies != RT_INDEFINITE_WAIT)
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| 215 | {
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| 216 | ts.tv_sec = cMillies / 1000;
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| 217 | ts.tv_nsec = (cMillies % 1000) * 1000000;
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| 218 | pTimeout = &ts;
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| 219 | }
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| 220 |
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| 221 | /*
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| 222 | * The wait loop.
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| 223 | */
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| 224 | for (unsigned i = 0;; i++)
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| 225 | {
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| 226 | /*
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| 227 | * Announce that we're among the waiters.
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| 228 | */
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| 229 | int32_t iNew = ASMAtomicIncS32(&pThis->cWaiters);
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| 230 | if (iNew == 0)
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| 231 | return VINF_SUCCESS;
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| 232 | if (RT_LIKELY(iNew > 0))
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| 233 | {
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| 234 | /*
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| 235 | * Go to sleep.
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| 236 | */
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| 237 | long rc = sys_futex(&pThis->cWaiters, FUTEX_WAIT, iNew, pTimeout, NULL, 0);
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| 238 | if (RT_UNLIKELY(pThis->iMagic != RTSEMEVENT_MAGIC))
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| 239 | return VERR_SEM_DESTROYED;
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| 240 |
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| 241 | /* Did somebody wake us up from RTSemEventSignal()? */
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| 242 | if (rc == 0)
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| 243 | return VINF_SUCCESS;
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| 244 |
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| 245 | /* No, then the kernel woke us up or we failed going to sleep. Adjust the accounting. */
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| 246 | iNew = ASMAtomicDecS32(&pThis->cWaiters);
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| 247 | Assert(iNew >= 0);
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| 248 |
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| 249 | /*
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| 250 | * Act on the wakup code.
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| 251 | */
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| 252 | if (rc == -ETIMEDOUT)
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| 253 | {
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| 254 | Assert(pTimeout);
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| 255 | return VERR_TIMEOUT;
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| 256 | }
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| 257 | if (rc == -EWOULDBLOCK)
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| 258 | /* retry with new value. */;
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| 259 | else if (rc == -EINTR)
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| 260 | {
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| 261 | if (!fAutoResume)
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| 262 | return VERR_INTERRUPTED;
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| 263 | }
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| 264 | else
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| 265 | {
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| 266 | /* this shouldn't happen! */
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| 267 | AssertMsgFailed(("rc=%ld errno=%d\n", rc, errno));
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| 268 | return RTErrConvertFromErrno(rc);
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| 269 | }
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| 270 | }
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| 271 | else
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| 272 | {
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| 273 | /* this can't happen. */
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| 274 | if (RT_UNLIKELY(pThis->iMagic != RTSEMEVENT_MAGIC))
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| 275 | return VERR_SEM_DESTROYED;
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| 276 | AssertReleaseMsgFailed(("iNew=%d\n", iNew));
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| 277 | }
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| 278 | }
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| 279 | }
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| 280 |
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| 281 |
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| 282 | RTDECL(int) RTSemEventWait(RTSEMEVENT EventSem, unsigned cMillies)
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| 283 | {
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| 284 | int rc = rtSemEventWait(EventSem, cMillies, true);
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| 285 | Assert(rc != VERR_INTERRUPTED);
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| 286 | Assert(rc != VERR_TIMEOUT || cMillies != RT_INDEFINITE_WAIT);
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| 287 | return rc;
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| 288 | }
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| 289 |
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| 290 |
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| 291 | RTDECL(int) RTSemEventWaitNoResume(RTSEMEVENT EventSem, unsigned cMillies)
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| 292 | {
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| 293 | return rtSemEventWait(EventSem, cMillies, false);
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| 294 | }
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| 295 |
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