/* $Id: semevent-linux.cpp 7639 2008-03-28 18:54:28Z vboxsync $ */ /** @file * innotek Portable Runtime - Event Semaphore, Linux (2.6.x+). */ /* * Copyright (C) 2006-2007 innotek GmbH * * This file is part of VirtualBox Open Source Edition (OSE), as * available from http://www.virtualbox.org. This file is free software; * you can redistribute it and/or modify it under the terms of the GNU * General Public License (GPL) as published by the Free Software * Foundation, in version 2 as it comes in the "COPYING" file of the * VirtualBox OSE distribution. VirtualBox OSE is distributed in the * hope that it will be useful, but WITHOUT ANY WARRANTY of any kind. * * The contents of this file may alternatively be used under the terms * of the Common Development and Distribution License Version 1.0 * (CDDL) only, as it comes in the "COPYING.CDDL" file of the * VirtualBox OSE distribution, in which case the provisions of the * CDDL are applicable instead of those of the GPL. * * You may elect to license modified versions of this file under the * terms and conditions of either the GPL or the CDDL or both. */ /******************************************************************************* * Header Files * *******************************************************************************/ #include #include #include #include #include #include "internal/magics.h" #include #include #include #include #include #include #if 0 /* With 2.6.17 futex.h has become C++ unfriendly. */ # include #else # define FUTEX_WAIT 0 # define FUTEX_WAKE 1 #endif /******************************************************************************* * Structures and Typedefs * *******************************************************************************/ /** * Linux (single wakup) event semaphore. */ struct RTSEMEVENTINTERNAL { /** Magic value. */ intptr_t volatile iMagic; /** The futex state variable. * <0 means signaled. * 0 means not signaled, no waiters. * >0 means not signaled, and the value gives the number of waiters. */ int32_t volatile cWaiters; }; /** * Wrapper for the futex syscall. */ static long sys_futex(int32_t volatile *uaddr, int op, int val, struct timespec *utime, int32_t *uaddr2, int val3) { errno = 0; long rc = syscall(__NR_futex, uaddr, op, val, utime, uaddr2, val3); if (rc < 0) { Assert(rc == -1); rc = -errno; } return rc; } RTDECL(int) RTSemEventCreate(PRTSEMEVENT pEventSem) { /* * Allocate semaphore handle. */ struct RTSEMEVENTINTERNAL *pThis = (struct RTSEMEVENTINTERNAL *)RTMemAlloc(sizeof(struct RTSEMEVENTINTERNAL)); if (pThis) { pThis->iMagic = RTSEMEVENT_MAGIC; pThis->cWaiters = 0; *pEventSem = pThis; return VINF_SUCCESS; } return VERR_NO_MEMORY; } RTDECL(int) RTSemEventDestroy(RTSEMEVENT EventSem) { /* * Validate input. */ struct RTSEMEVENTINTERNAL *pThis = EventSem; AssertReturn(VALID_PTR(pThis) && pThis->iMagic == RTSEMEVENT_MAGIC, VERR_INVALID_HANDLE); /* * Invalidate the semaphore and wake up anyone waiting on it. */ ASMAtomicXchgSize(&pThis->iMagic, RTSEMEVENT_MAGIC + 1); if (ASMAtomicXchgS32(&pThis->cWaiters, INT32_MIN / 2) > 0) { sys_futex(&pThis->cWaiters, FUTEX_WAKE, INT_MAX, NULL, NULL, 0); usleep(1000); } /* * Free the semaphore memory and be gone. */ RTMemFree(pThis); return VINF_SUCCESS; } RTDECL(int) RTSemEventSignal(RTSEMEVENT EventSem) { /* * Validate input. */ struct RTSEMEVENTINTERNAL *pThis = EventSem; AssertReturn(VALID_PTR(pThis) && pThis->iMagic == RTSEMEVENT_MAGIC, VERR_INVALID_HANDLE); /* * Try signal it. */ for (unsigned i = 0;; i++) { int32_t iCur = pThis->cWaiters; if (iCur == 0) { if (ASMAtomicCmpXchgS32(&pThis->cWaiters, -1, 0)) break; /* nobody is waiting */ } else if (iCur < 0) break; /* already signaled */ else { /* somebody is waiting, try wake up one of them. */ long cWoken = sys_futex(&pThis->cWaiters, FUTEX_WAKE, 1, NULL, NULL, 0); if (RT_LIKELY(cWoken == 1)) { ASMAtomicDecS32(&pThis->cWaiters); break; } AssertMsg(cWoken == 0, ("%ld\n", cWoken)); /* * This path is taken in two situations: * 1) A waiting thread is returning from the sys_futex call with a * non-zero return value. * 2) There are two threads signaling the event at the * same time and only one thread waiting. * * At this point we know that nobody is activly waiting on the event but * at the same time, we are racing someone updating the state. The current * strategy is to spin till the thread racing us is done, this is kind of * brain dead and need fixing of course. */ if (RT_UNLIKELY(i > 32)) { if ((i % 128) == 127) usleep(1000); else if (!(i % 4)) pthread_yield(); else AssertReleaseMsg(i < 4096, ("iCur=%#x pThis=%p\n", iCur, pThis)); } } } return VINF_SUCCESS; } static int rtSemEventWait(RTSEMEVENT EventSem, unsigned cMillies, bool fAutoResume) { /* * Validate input. */ struct RTSEMEVENTINTERNAL *pThis = EventSem; AssertReturn(VALID_PTR(pThis) && pThis->iMagic == RTSEMEVENT_MAGIC, VERR_INVALID_HANDLE); /* * Quickly check whether it's signaled. */ if (ASMAtomicCmpXchgS32(&pThis->cWaiters, 0, -1)) return VINF_SUCCESS; /* * Convert timeout value. */ struct timespec ts; struct timespec *pTimeout = NULL; if (cMillies != RT_INDEFINITE_WAIT) { ts.tv_sec = cMillies / 1000; ts.tv_nsec = (cMillies % 1000) * 1000000; pTimeout = &ts; } /* * The wait loop. */ for (unsigned i = 0;; i++) { /* * Announce that we're among the waiters. */ int32_t iNew = ASMAtomicIncS32(&pThis->cWaiters); if (iNew == 0) return VINF_SUCCESS; if (RT_LIKELY(iNew > 0)) { /* * Go to sleep. */ long rc = sys_futex(&pThis->cWaiters, FUTEX_WAIT, iNew, pTimeout, NULL, 0); if (RT_UNLIKELY(pThis->iMagic != RTSEMEVENT_MAGIC)) return VERR_SEM_DESTROYED; /* Did somebody wake us up from RTSemEventSignal()? */ if (rc == 0) return VINF_SUCCESS; /* No, then the kernel woke us up or we failed going to sleep. Adjust the accounting. */ iNew = ASMAtomicDecS32(&pThis->cWaiters); Assert(iNew >= 0); /* * Act on the wakup code. */ if (rc == -ETIMEDOUT) { Assert(pTimeout); return VERR_TIMEOUT; } if (rc == -EWOULDBLOCK) /* retry with new value. */; else if (rc == -EINTR) { if (!fAutoResume) return VERR_INTERRUPTED; } else { /* this shouldn't happen! */ AssertMsgFailed(("rc=%ld errno=%d\n", rc, errno)); return RTErrConvertFromErrno(rc); } } else { /* this can't happen. */ if (RT_UNLIKELY(pThis->iMagic != RTSEMEVENT_MAGIC)) return VERR_SEM_DESTROYED; AssertReleaseMsgFailed(("iNew=%d\n", iNew)); } } } RTDECL(int) RTSemEventWait(RTSEMEVENT EventSem, unsigned cMillies) { int rc = rtSemEventWait(EventSem, cMillies, true); Assert(rc != VERR_INTERRUPTED); Assert(rc != VERR_TIMEOUT || cMillies != RT_INDEFINITE_WAIT); return rc; } RTDECL(int) RTSemEventWaitNoResume(RTSEMEVENT EventSem, unsigned cMillies) { return rtSemEventWait(EventSem, cMillies, false); }