1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
|
/* $Id: once.cpp $ */
/** @file
* IPRT - Execute Once.
*/
/*
* Copyright (C) 2007 Sun Microsystems, Inc.
*
* 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.
*
* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa
* Clara, CA 95054 USA or visit http://www.sun.com if you need
* additional information or have any questions.
*/
/*******************************************************************************
* Header Files *
*******************************************************************************/
#include <iprt/once.h>
#include <iprt/semaphore.h>
#include <iprt/thread.h>
#include <iprt/err.h>
#include <iprt/assert.h>
#include <iprt/asm.h>
RTDECL(int) RTOnce(PRTONCE pOnce, PFNRTONCE pfnOnce, void *pvUser1, void *pvUser2)
{
/*
* Validate input (strict builds only).
*/
AssertPtr(pOnce);
AssertPtr(pfnOnce);
/*
* Deal with the 'initialized' case first
*/
int32_t iState = ASMAtomicUoReadS32(&pOnce->iState);
if (RT_LIKELY(iState == 2))
return ASMAtomicUoReadS32(&pOnce->rc);
AssertReturn(iState == -1 || iState == 1, VERR_INTERNAL_ERROR);
/*
* Do we initialize it?
*/
if (iState == -1)
{
RTSEMEVENTMULTI hEventMulti;
int rc = RTSemEventMultiCreate(&hEventMulti);
if (RT_FAILURE(rc))
hEventMulti = NIL_RTSEMEVENTMULTI;
if (ASMAtomicCmpXchgS32(&pOnce->iState, 1, -1))
{
ASMAtomicWriteHandle(&pOnce->hEventMulti, hEventMulti);
ASMAtomicIncS32(&pOnce->cEventRefs);
/* do the execute once stuff. */
int32_t rcOnce = pfnOnce(pvUser1, pvUser2);
/* set the return code, change the state and signal any waiters. */
ASMAtomicWriteS32(&pOnce->rc, rcOnce);
ASMAtomicWriteS32(&pOnce->iState, 2);
if (hEventMulti != NIL_RTSEMEVENTMULTI)
RTSemEventMultiSignal(hEventMulti);
/* last guy destroys the semaphore. */
if (ASMAtomicDecS32(&pOnce->cEventRefs) == 0)
ASMAtomicWriteSize(&pOnce->hEventMulti, NIL_RTSEMEVENTMULTI);
else
hEventMulti = NIL_RTSEMEVENTMULTI;
}
if (hEventMulti != NIL_RTSEMEVENTMULTI)
RTSemEventMultiDestroy(hEventMulti);
}
/*
* Wait for it to finish initializing.
*/
if (ASMAtomicReadS32(&pOnce->iState) == 1)
{
int i = 0;
while (ASMAtomicReadS32(&pOnce->iState) == 1)
{
bool fYieldSleep = true;
/*
* Take care not to increment the counter if it's 0, that indicates
* that RTONCE::hEventMulti isn't valid either because it's not set
* yet, or because it's being destroyed.
*/
int32_t cEventRefs = ASMAtomicUoReadS32(&pOnce->cEventRefs);
while ( cEventRefs > 0
&& !ASMAtomicCmpXchgS32(&pOnce->cEventRefs, cEventRefs + 1, cEventRefs))
cEventRefs = ASMAtomicUoReadS32(&pOnce->cEventRefs);
if (cEventRefs > 1)
{
/*
* The hEventMulti might be NIL for two reasons, see above in
* the init code, if it isn't valid just do the yield/sleep thing.
*/
RTSEMEVENTMULTI hEventMulti;
ASMAtomicUoReadSize(&pOnce->hEventMulti, &hEventMulti);
if (hEventMulti != NIL_RTSEMEVENTMULTI)
{
fYieldSleep = false;
RTSemEventMultiWait(hEventMulti, RT_INDEFINITE_WAIT);
}
/*
* Last thread cleans up.
*/
if (ASMAtomicDecS32(&pOnce->cEventRefs) == 0)
{
ASMAtomicXchgHandle(&pOnce->hEventMulti, NIL_RTSEMEVENTMULTI, &hEventMulti);
if (hEventMulti != NIL_RTSEMEVENTMULTI)
RTSemEventMultiDestroy(hEventMulti);
}
}
/*
* If we didn't block, yield or sleep for a bit.
*
* The sleep is essential to prevent higher priority threads from spinning wildly
* and preventing a lower priority thread from completing the pfnOnce operation
* in a timely manner.
*/
if (fYieldSleep)
{
if (ASMAtomicReadS32(&pOnce->iState) != 1)
break;
if (!(++i % 8) )
RTThreadSleep(1);
else
RTThreadYield();
}
}
}
/*
* Finally, return the status code from the execute once function.
*/
return ASMAtomicUoReadS32(&pOnce->rc);
}
|
