| 1 | /* $Id: semevent-linux.cpp 14468 2008-11-21 15:44:27Z 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 | #include <features.h>
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| 32 | #if __GLIBC_PREREQ(2,6)
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| 33 |
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| 34 | /*
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| 35 | * glibc 2.6 fixed a serious bug in the mutex implementation. We wrote this
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| 36 | * linux specific event semaphores code in order to work around the bug. As it
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| 37 | * turns out, this code seems to have an unresolved issue (#2599), so we'll
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| 38 | * fall back on the pthread based implementation if glibc is known to contain
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| 39 | * the bug fix.
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| 40 | *
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| 41 | * The external refernce to epoll_pwait is a hack which prevents that we link
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| 42 | * against glibc < 2.6.
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| 43 | */
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| 44 | #include "../posix/semevent-posix.cpp"
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| 45 | asm volatile (".global epoll_pwait");
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| 46 |
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| 47 | #else /* glibc < 2.6 */
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| 48 |
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| 49 | /*******************************************************************************
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| 50 | * Header Files *
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| 51 | *******************************************************************************/
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| 52 | #include <iprt/semaphore.h>
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| 53 | #include <iprt/assert.h>
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| 54 | #include <iprt/alloc.h>
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| 55 | #include <iprt/asm.h>
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| 56 | #include <iprt/err.h>
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| 57 | #include "internal/magics.h"
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| 58 |
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| 59 | #include <errno.h>
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| 60 | #include <limits.h>
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| 61 | #include <pthread.h>
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| 62 | #include <unistd.h>
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| 63 | #include <sys/time.h>
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| 64 | #include <sys/syscall.h>
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| 65 | #if 0 /* With 2.6.17 futex.h has become C++ unfriendly. */
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| 66 | # include <linux/futex.h>
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| 67 | #else
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| 68 | # define FUTEX_WAIT 0
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| 69 | # define FUTEX_WAKE 1
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| 70 | #endif
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| 71 |
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| 72 |
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| 73 | /*******************************************************************************
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| 74 | * Structures and Typedefs *
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| 75 | *******************************************************************************/
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| 76 | /**
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| 77 | * Linux (single wakup) event semaphore.
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| 78 | */
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| 79 | struct RTSEMEVENTINTERNAL
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| 80 | {
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| 81 | /** Magic value. */
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| 82 | intptr_t volatile iMagic;
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| 83 | /** The futex state variable.
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| 84 | * <0 means signaled.
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| 85 | * 0 means not signaled, no waiters.
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| 86 | * >0 means not signaled, and the value gives the number of waiters.
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| 87 | */
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| 88 | int32_t volatile cWaiters;
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| 89 | };
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| 90 |
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| 91 |
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| 92 | /**
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| 93 | * Wrapper for the futex syscall.
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| 94 | */
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| 95 | static long sys_futex(int32_t volatile *uaddr, int op, int val, struct timespec *utime, int32_t *uaddr2, int val3)
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| 96 | {
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| 97 | errno = 0;
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| 98 | long rc = syscall(__NR_futex, uaddr, op, val, utime, uaddr2, val3);
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| 99 | if (rc < 0)
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| 100 | {
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| 101 | Assert(rc == -1);
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| 102 | rc = -errno;
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| 103 | }
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| 104 | return rc;
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| 105 | }
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| 106 |
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| 107 |
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| 108 |
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| 109 | RTDECL(int) RTSemEventCreate(PRTSEMEVENT pEventSem)
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| 110 | {
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| 111 | /*
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| 112 | * Allocate semaphore handle.
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| 113 | */
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| 114 | struct RTSEMEVENTINTERNAL *pThis = (struct RTSEMEVENTINTERNAL *)RTMemAlloc(sizeof(struct RTSEMEVENTINTERNAL));
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| 115 | if (pThis)
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| 116 | {
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| 117 | pThis->iMagic = RTSEMEVENT_MAGIC;
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| 118 | pThis->cWaiters = 0;
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| 119 | *pEventSem = pThis;
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| 120 | return VINF_SUCCESS;
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| 121 | }
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| 122 | return VERR_NO_MEMORY;
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| 123 | }
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| 124 |
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| 125 |
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| 126 | RTDECL(int) RTSemEventDestroy(RTSEMEVENT EventSem)
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| 127 | {
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| 128 | /*
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| 129 | * Validate input.
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| 130 | */
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| 131 | if (EventSem == NIL_RTSEMEVENT) /* don't bitch */
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| 132 | return VERR_INVALID_HANDLE;
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| 133 | struct RTSEMEVENTINTERNAL *pThis = EventSem;
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| 134 | AssertPtrReturn(pThis, VERR_INVALID_HANDLE);
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| 135 | AssertReturn(pThis->iMagic == RTSEMEVENT_MAGIC, VERR_INVALID_HANDLE);
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| 136 |
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| 137 | /*
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| 138 | * Invalidate the semaphore and wake up anyone waiting on it.
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| 139 | */
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| 140 | ASMAtomicXchgSize(&pThis->iMagic, RTSEMEVENT_MAGIC | UINT32_C(0x80000000));
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| 141 | if (ASMAtomicXchgS32(&pThis->cWaiters, INT32_MIN / 2) > 0)
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| 142 | {
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| 143 | sys_futex(&pThis->cWaiters, FUTEX_WAKE, INT_MAX, NULL, NULL, 0);
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| 144 | usleep(1000);
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| 145 | }
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| 146 |
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| 147 | /*
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| 148 | * Free the semaphore memory and be gone.
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| 149 | */
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| 150 | RTMemFree(pThis);
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| 151 | return VINF_SUCCESS;
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| 152 | }
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| 153 |
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| 154 |
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| 155 | RTDECL(int) RTSemEventSignal(RTSEMEVENT EventSem)
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| 156 | {
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| 157 | /*
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| 158 | * Validate input.
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| 159 | */
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| 160 | struct RTSEMEVENTINTERNAL *pThis = EventSem;
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| 161 | AssertReturn(VALID_PTR(pThis) && pThis->iMagic == RTSEMEVENT_MAGIC,
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| 162 | VERR_INVALID_HANDLE);
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| 163 | /*
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| 164 | * Try signal it.
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| 165 | */
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| 166 | for (unsigned i = 0;; i++)
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| 167 | {
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| 168 | int32_t iCur;
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| 169 | if (ASMAtomicCmpXchgExS32(&pThis->cWaiters, -1, 0, &iCur))
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| 170 | break; /* nobody is waiting */
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| 171 | else if (iCur < 0)
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| 172 | break; /* already signaled */
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| 173 | else
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| 174 | {
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| 175 | /* somebody is waiting, try wake up one of them. */
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| 176 | long cWoken = sys_futex(&pThis->cWaiters, FUTEX_WAKE, 1, NULL, NULL, 0);
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| 177 | if (RT_LIKELY(cWoken == 1))
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| 178 | {
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| 179 | ASMAtomicDecS32(&pThis->cWaiters);
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| 180 | break;
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| 181 | }
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| 182 | AssertMsg(cWoken == 0, ("%ld\n", cWoken));
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| 183 |
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| 184 | /*
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| 185 | * This path is taken in two situations:
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| 186 | * 1) A waiting thread is returning from the sys_futex call with a
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| 187 | * non-zero return value.
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| 188 | * 2) There are two threads signaling the event at the
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| 189 | * same time and only one thread waiting.
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| 190 | *
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| 191 | * At this point we know that nobody is activly waiting on the event but
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| 192 | * at the same time, we are racing someone updating the state. The current
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| 193 | * strategy is to spin till the thread racing us is done, this is kind of
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| 194 | * brain dead and need fixing of course.
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| 195 | */
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| 196 | if (RT_UNLIKELY(i > 32))
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| 197 | {
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| 198 | if ((i % 128) == 127)
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| 199 | usleep(1000);
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| 200 | else if (!(i % 4))
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| 201 | pthread_yield();
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| 202 | else
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| 203 | AssertReleaseMsg(i < 4096, ("iCur=%#x pThis=%p\n", iCur, pThis));
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| 204 | }
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| 205 | }
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| 206 |
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| 207 | /* Check the magic to fend off races with RTSemEventDestroy. */
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| 208 | if (RT_UNLIKELY(pThis->iMagic != RTSEMEVENT_MAGIC))
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| 209 | return VERR_SEM_DESTROYED;
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| 210 | }
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| 211 | return VINF_SUCCESS;
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| 212 | }
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| 213 |
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| 214 |
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| 215 | static int rtSemEventWait(RTSEMEVENT EventSem, unsigned cMillies, bool fAutoResume)
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| 216 | {
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| 217 | /*
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| 218 | * Validate input.
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| 219 | */
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| 220 | struct RTSEMEVENTINTERNAL *pThis = EventSem;
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| 221 | AssertReturn(VALID_PTR(pThis) && pThis->iMagic == RTSEMEVENT_MAGIC,
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| 222 | VERR_INVALID_HANDLE);
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| 223 |
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| 224 | /*
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| 225 | * Quickly check whether it's signaled.
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| 226 | */
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| 227 | if (ASMAtomicCmpXchgS32(&pThis->cWaiters, 0, -1))
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| 228 | return VINF_SUCCESS;
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| 229 |
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| 230 | /*
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| 231 | * Convert timeout value.
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| 232 | */
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| 233 | struct timespec ts;
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| 234 | struct timespec *pTimeout = NULL;
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| 235 | if (cMillies != RT_INDEFINITE_WAIT)
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| 236 | {
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| 237 | ts.tv_sec = cMillies / 1000;
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| 238 | ts.tv_nsec = (cMillies % 1000) * 1000000;
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| 239 | pTimeout = &ts;
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| 240 | }
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| 241 |
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| 242 | /*
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| 243 | * The wait loop.
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| 244 | */
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| 245 | for (unsigned i = 0;; i++)
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| 246 | {
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| 247 | /*
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| 248 | * Announce that we're among the waiters.
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| 249 | */
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| 250 | int32_t iNew = ASMAtomicIncS32(&pThis->cWaiters);
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| 251 | if (iNew == 0)
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| 252 | return VINF_SUCCESS;
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| 253 | if (RT_LIKELY(iNew > 0))
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| 254 | {
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| 255 | /*
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| 256 | * Go to sleep.
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| 257 | */
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| 258 | long rc = sys_futex(&pThis->cWaiters, FUTEX_WAIT, iNew, pTimeout, NULL, 0);
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| 259 | if (RT_UNLIKELY(pThis->iMagic != RTSEMEVENT_MAGIC))
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| 260 | return VERR_SEM_DESTROYED;
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| 261 |
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| 262 | /* Did somebody wake us up from RTSemEventSignal()? */
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| 263 | if (rc == 0)
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| 264 | return VINF_SUCCESS;
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| 265 |
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| 266 | /* No, then the kernel woke us up or we failed going to sleep. Adjust the accounting. */
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| 267 | iNew = ASMAtomicDecS32(&pThis->cWaiters);
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| 268 | Assert(iNew >= 0);
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| 269 |
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| 270 | /*
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| 271 | * Act on the wakup code.
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| 272 | */
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| 273 | if (rc == -ETIMEDOUT)
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| 274 | {
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| 275 | Assert(pTimeout);
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| 276 | return VERR_TIMEOUT;
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| 277 | }
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| 278 | if (rc == -EWOULDBLOCK)
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| 279 | /* retry with new value. */;
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| 280 | else if (rc == -EINTR)
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| 281 | {
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| 282 | if (!fAutoResume)
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| 283 | return VERR_INTERRUPTED;
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| 284 | }
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| 285 | else
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| 286 | {
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| 287 | /* this shouldn't happen! */
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| 288 | AssertMsgFailed(("rc=%ld errno=%d\n", rc, errno));
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| 289 | return RTErrConvertFromErrno(rc);
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| 290 | }
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| 291 | }
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| 292 | else
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| 293 | {
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| 294 | /* this can't happen. */
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| 295 | if (RT_UNLIKELY(pThis->iMagic != RTSEMEVENT_MAGIC))
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| 296 | return VERR_SEM_DESTROYED;
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| 297 | AssertReleaseMsgFailed(("iNew=%d\n", iNew));
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| 298 | }
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| 299 | }
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| 300 | }
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| 301 |
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| 302 |
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| 303 | RTDECL(int) RTSemEventWait(RTSEMEVENT EventSem, unsigned cMillies)
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| 304 | {
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| 305 | int rc = rtSemEventWait(EventSem, cMillies, true);
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| 306 | Assert(rc != VERR_INTERRUPTED);
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| 307 | Assert(rc != VERR_TIMEOUT || cMillies != RT_INDEFINITE_WAIT);
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| 308 | return rc;
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| 309 | }
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| 310 |
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| 311 |
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| 312 | RTDECL(int) RTSemEventWaitNoResume(RTSEMEVENT EventSem, unsigned cMillies)
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| 313 | {
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| 314 | return rtSemEventWait(EventSem, cMillies, false);
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| 315 | }
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| 316 |
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| 317 | #endif /* glibc < 2.6 */
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