semevent-linux.cpp@ 7019

Last change on this file since 7019 was 6747, checked in by vboxsync, 17 years ago
pInt[Event\|EventMulti\|Mutex]Sem -> pThis
Property svn:eol-style set to `native` Property svn:keywords set to `Id`
File size: 8.3 KB

Line
1	/* $Id: semevent-linux.cpp 6747 2008-02-02 00:57:41Z vboxsync $ */
2	/** @file
3	* innotek Portable Runtime - Event Semaphore, Linux (2.6.x+).
4	*/
5
6	/*
7	* Copyright (C) 2006-2007 innotek GmbH
8	*
9	* This file is part of VirtualBox Open Source Edition (OSE), as
10	* available from http://www.virtualbox.org. This file is free software;
11	* you can redistribute it and/or modify it under the terms of the GNU
12	* General Public License (GPL) as published by the Free Software
13	* Foundation, in version 2 as it comes in the "COPYING" file of the
14	* VirtualBox OSE distribution. VirtualBox OSE is distributed in the
15	* hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
16	*
17	* The contents of this file may alternatively be used under the terms
18	* of the Common Development and Distribution License Version 1.0
19	* (CDDL) only, as it comes in the "COPYING.CDDL" file of the
20	* VirtualBox OSE distribution, in which case the provisions of the
21	* CDDL are applicable instead of those of the GPL.
22	*
23	* You may elect to license modified versions of this file under the
24	* terms and conditions of either the GPL or the CDDL or both.
25	*/
26
27	/*******************************************************************************
28	* Header Files *
29	*******************************************************************************/
30	#include <iprt/semaphore.h>
31	#include <iprt/assert.h>
32	#include <iprt/alloc.h>
33	#include <iprt/asm.h>
34	#include <iprt/err.h>
35	#include "internal/magics.h"
36
37	#include <errno.h>
38	#include <limits.h>
39	#include <pthread.h>
40	#include <unistd.h>
41	#include <sys/time.h>
42	#include <sys/syscall.h>
43	#if 0 /* With 2.6.17 futex.h has become C++ unfriendly. */
44	# include <linux/futex.h>
45	#else
46	# define FUTEX_WAIT 0
47	# define FUTEX_WAKE 1
48	#endif
49
50
51	/*******************************************************************************
52	* Structures and Typedefs *
53	*******************************************************************************/
54	/**
55	* Linux (single wakup) event semaphore.
56	*/
57	struct RTSEMEVENTINTERNAL
58	{
59	/** Magic value. */
60	intptr_t volatile iMagic;
61	/** The futex state variable.
62	* <0 means signaled.
63	* 0 means not signaled, no waiters.
64	* >0 means not signaled, and the value gives the number of waiters.
65	*/
66	int32_t volatile cWaiters;
67	};
68
69
70	/**
71	* Wrapper for the futex syscall.
72	*/
73	static long sys_futex(int32_t volatile uaddr, int op, int val, struct timespec utime, int32_t *uaddr2, int val3)
74	{
75	errno = 0;
76	long rc = syscall(__NR_futex, uaddr, op, val, utime, uaddr2, val3);
77	if (rc < 0)
78	{
79	Assert(rc == -1);
80	rc = -errno;
81	}
82	return rc;
83	}
84
85
86
87	RTDECL(int) RTSemEventCreate(PRTSEMEVENT pEventSem)
88	{
89	/*
90	* Allocate semaphore handle.
91	*/
92	struct RTSEMEVENTINTERNAL pThis = (struct RTSEMEVENTINTERNAL )RTMemAlloc(sizeof(struct RTSEMEVENTINTERNAL));
93	if (pThis)
94	{
95	pThis->iMagic = RTSEMEVENT_MAGIC;
96	pThis->cWaiters = 0;
97	*pEventSem = pThis;
98	return VINF_SUCCESS;
99	}
100	return VERR_NO_MEMORY;
101	}
102
103
104	RTDECL(int) RTSemEventDestroy(RTSEMEVENT EventSem)
105	{
106	/*
107	* Validate input.
108	*/
109	struct RTSEMEVENTINTERNAL *pThis = EventSem;
110	AssertReturn(VALID_PTR(pThis) && pThis->iMagic == RTSEMEVENT_MAGIC,
111	VERR_INVALID_HANDLE);
112
113	/*
114	* Invalidate the semaphore and wake up anyone waiting on it.
115	*/
116	ASMAtomicXchgSize(&pThis->iMagic, RTSEMEVENT_MAGIC + 1);
117	if (ASMAtomicXchgS32(&pThis->cWaiters, INT32_MIN / 2) > 0)
118	{
119	sys_futex(&pThis->cWaiters, FUTEX_WAKE, INT_MAX, NULL, NULL, 0);
120	usleep(1000);
121	}
122
123	/*
124	* Free the semaphore memory and be gone.
125	*/
126	RTMemFree(pThis);
127	return VINF_SUCCESS;
128	}
129
130
131	RTDECL(int) RTSemEventSignal(RTSEMEVENT EventSem)
132	{
133	/*
134	* Validate input.
135	*/
136	struct RTSEMEVENTINTERNAL *pThis = EventSem;
137	AssertReturn(VALID_PTR(pThis) && pThis->iMagic == RTSEMEVENT_MAGIC,
138	VERR_INVALID_HANDLE);
139	/*
140	* Try signal it.
141	*/
142	for (unsigned i = 0;; i++)
143	{
144	int32_t iCur = pThis->cWaiters;
145	if (iCur == 0)
146	{
147	if (ASMAtomicCmpXchgS32(&pThis->cWaiters, -1, 0))
148	break; /* nobody is waiting */
149	}
150	else if (iCur < 0)
151	break; /* already signaled */
152	else
153	{
154	/* somebody is waiting, try wake up one of them. */
155	long cWoken = sys_futex(&pThis->cWaiters, FUTEX_WAKE, 1, NULL, NULL, 0);
156	if (RT_LIKELY(cWoken == 1))
157	{
158	ASMAtomicDecS32(&pThis->cWaiters);
159	break;
160	}
161	AssertMsg(cWoken == 0, ("%ld\n", cWoken));
162
163	/*
164	* This path is taken in two situations:
165	* 1) A waiting thread is returning from the sys_futex call with a
166	* non-zero return value.
167	* 2) There are two threads signaling the event at the
168	* same time and only one thread waiting.
169	*
170	* At this point we know that nobody is activly waiting on the event but
171	* at the same time, we are racing someone updating the state. The current
172	* strategy is to spin till the thread racing us is done, this is kind of
173	* brain dead and need fixing of course.
174	*/
175	if (RT_UNLIKELY(i > 32))
176	{
177	if ((i % 128) == 127)
178	usleep(1000);
179	else if (!(i % 4))
180	pthread_yield();
181	else
182	AssertReleaseMsg(i < 4096, ("iCur=%#x pThis=%p\n", iCur, pThis));
183	}
184	}
185	}
186	return VINF_SUCCESS;
187	}
188
189
190	static int rtSemEventWait(RTSEMEVENT EventSem, unsigned cMillies, bool fAutoResume)
191	{
192	/*
193	* Validate input.
194	*/
195	struct RTSEMEVENTINTERNAL *pThis = EventSem;
196	AssertReturn(VALID_PTR(pThis) && pThis->iMagic == RTSEMEVENT_MAGIC,
197	VERR_INVALID_HANDLE);
198
199	/*
200	* Quickly check whether it's signaled.
201	*/
202	if (ASMAtomicCmpXchgS32(&pThis->cWaiters, 0, -1))
203	return VINF_SUCCESS;
204
205	/*
206	* Convert timeout value.
207	*/
208	struct timespec ts;
209	struct timespec *pTimeout = 0;
210	if (cMillies != RT_INDEFINITE_WAIT)
211	{
212	ts.tv_sec = cMillies / 1000;
213	ts.tv_nsec = (cMillies % 1000) * 1000000;
214	pTimeout = &ts;
215	}
216
217	/*
218	* The wait loop.
219	*/
220	for (unsigned i = 0;; i++)
221	{
222	/*
223	* Announce that we're among the waiters.
224	*/
225	int32_t iNew = ASMAtomicIncS32(&pThis->cWaiters);
226	if (iNew == 0)
227	return VINF_SUCCESS;
228	if (RT_LIKELY(iNew > 0))
229	{
230	/*
231	* Go to sleep.
232	*/
233	long rc = sys_futex(&pThis->cWaiters, FUTEX_WAIT, iNew, pTimeout, NULL, 0);
234	if (RT_UNLIKELY(pThis->iMagic != RTSEMEVENT_MAGIC))
235	return VERR_SEM_DESTROYED;
236
237	/* Did somebody wake us up from RTSemEventSignal()? */
238	if (rc == 0)
239	return VINF_SUCCESS;
240
241	/* No, then the kernel woke us up or we failed going to sleep. Adjust the accounting. */
242	iNew = ASMAtomicDecS32(&pThis->cWaiters);
243	Assert(iNew >= 0);
244
245	/*
246	* Act on the wakup code.
247	*/
248	if (rc == -ETIMEDOUT)
249	{
250	Assert(pTimeout);
251	return VERR_TIMEOUT;
252	}
253	if (rc == -EWOULDBLOCK)
254	/* retry with new value. */;
255	else if (rc == -EINTR)
256	{
257	if (!fAutoResume)
258	return VERR_INTERRUPTED;
259	}
260	else
261	{
262	/* this shouldn't happen! */
263	AssertMsgFailed(("rc=%ld errno=%d\n", rc, errno));
264	return RTErrConvertFromErrno(rc);
265	}
266	}
267	else
268	{
269	/* this can't happen. */
270	if (RT_UNLIKELY(pThis->iMagic != RTSEMEVENT_MAGIC))
271	return VERR_SEM_DESTROYED;
272	AssertReleaseMsgFailed(("iNew=%d\n", iNew));
273	}
274	}
275	}
276
277
278	RTDECL(int) RTSemEventWait(RTSEMEVENT EventSem, unsigned cMillies)
279	{
280	int rc = rtSemEventWait(EventSem, cMillies, true);
281	Assert(rc != VERR_INTERRUPTED);
282	return rc;
283	}
284
285
286	RTDECL(int) RTSemEventWaitNoResume(RTSEMEVENT EventSem, unsigned cMillies)
287	{
288	return rtSemEventWait(EventSem, cMillies, false);
289	}
290

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source: vbox/trunk/src/VBox/Runtime/r3/linux/semevent-linux.cpp@ 7019

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