1 /******************************************************************************
2  *
3  * Module Name: utlock - Reader/Writer lock interfaces
4  *
5  *****************************************************************************/
6 
7 /*
8  * Copyright (C) 2000 - 2014, Intel Corp.
9  * All rights reserved.
10  *
11  * Redistribution and use in source and binary forms, with or without
12  * modification, are permitted provided that the following conditions
13  * are met:
14  * 1. Redistributions of source code must retain the above copyright
15  *    notice, this list of conditions, and the following disclaimer,
16  *    without modification.
17  * 2. Redistributions in binary form must reproduce at minimum a disclaimer
18  *    substantially similar to the "NO WARRANTY" disclaimer below
19  *    ("Disclaimer") and any redistribution must be conditioned upon
20  *    including a substantially similar Disclaimer requirement for further
21  *    binary redistribution.
22  * 3. Neither the names of the above-listed copyright holders nor the names
23  *    of any contributors may be used to endorse or promote products derived
24  *    from this software without specific prior written permission.
25  *
26  * Alternatively, this software may be distributed under the terms of the
27  * GNU General Public License ("GPL") version 2 as published by the Free
28  * Software Foundation.
29  *
30  * NO WARRANTY
31  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
32  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
33  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR
34  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
35  * HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
36  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
37  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
38  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
39  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
40  * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
41  * POSSIBILITY OF SUCH DAMAGES.
42  */
43 
44 #define __UTLOCK_C__
45 
46 #include "acpi.h"
47 #include "accommon.h"
48 
49 
50 #define _COMPONENT          ACPI_UTILITIES
51         ACPI_MODULE_NAME    ("utlock")
52 
53 
54 /*******************************************************************************
55  *
56  * FUNCTION:    AcpiUtCreateRwLock
57  *              AcpiUtDeleteRwLock
58  *
59  * PARAMETERS:  Lock                - Pointer to a valid RW lock
60  *
61  * RETURN:      Status
62  *
63  * DESCRIPTION: Reader/writer lock creation and deletion interfaces.
64  *
65  ******************************************************************************/
66 
67 ACPI_STATUS
68 AcpiUtCreateRwLock (
69     ACPI_RW_LOCK            *Lock)
70 {
71     ACPI_STATUS             Status;
72 
73 
74     Lock->NumReaders = 0;
75     Status = AcpiOsCreateMutex (&Lock->ReaderMutex);
76     if (ACPI_FAILURE (Status))
77     {
78         return (Status);
79     }
80 
81     Status = AcpiOsCreateMutex (&Lock->WriterMutex);
82     return (Status);
83 }
84 
85 
86 void
87 AcpiUtDeleteRwLock (
88     ACPI_RW_LOCK            *Lock)
89 {
90 
91     AcpiOsDeleteMutex (Lock->ReaderMutex);
92     AcpiOsDeleteMutex (Lock->WriterMutex);
93 
94     Lock->NumReaders = 0;
95     Lock->ReaderMutex = NULL;
96     Lock->WriterMutex = NULL;
97 }
98 
99 
100 /*******************************************************************************
101  *
102  * FUNCTION:    AcpiUtAcquireReadLock
103  *              AcpiUtReleaseReadLock
104  *
105  * PARAMETERS:  Lock                - Pointer to a valid RW lock
106  *
107  * RETURN:      Status
108  *
109  * DESCRIPTION: Reader interfaces for reader/writer locks. On acquisition,
110  *              only the first reader acquires the write mutex. On release,
111  *              only the last reader releases the write mutex. Although this
112  *              algorithm can in theory starve writers, this should not be a
113  *              problem with ACPICA since the subsystem is infrequently used
114  *              in comparison to (for example) an I/O system.
115  *
116  ******************************************************************************/
117 
118 ACPI_STATUS
119 AcpiUtAcquireReadLock (
120     ACPI_RW_LOCK            *Lock)
121 {
122     ACPI_STATUS             Status;
123 
124 
125     Status = AcpiOsAcquireMutex (Lock->ReaderMutex, ACPI_WAIT_FOREVER);
126     if (ACPI_FAILURE (Status))
127     {
128         return (Status);
129     }
130 
131     /* Acquire the write lock only for the first reader */
132 
133     Lock->NumReaders++;
134     if (Lock->NumReaders == 1)
135     {
136         Status = AcpiOsAcquireMutex (Lock->WriterMutex, ACPI_WAIT_FOREVER);
137     }
138 
139     AcpiOsReleaseMutex (Lock->ReaderMutex);
140     return (Status);
141 }
142 
143 
144 ACPI_STATUS
145 AcpiUtReleaseReadLock (
146     ACPI_RW_LOCK            *Lock)
147 {
148     ACPI_STATUS             Status;
149 
150 
151     Status = AcpiOsAcquireMutex (Lock->ReaderMutex, ACPI_WAIT_FOREVER);
152     if (ACPI_FAILURE (Status))
153     {
154         return (Status);
155     }
156 
157     /* Release the write lock only for the very last reader */
158 
159     Lock->NumReaders--;
160     if (Lock->NumReaders == 0)
161     {
162         AcpiOsReleaseMutex (Lock->WriterMutex);
163     }
164 
165     AcpiOsReleaseMutex (Lock->ReaderMutex);
166     return (Status);
167 }
168 
169 
170 /*******************************************************************************
171  *
172  * FUNCTION:    AcpiUtAcquireWriteLock
173  *              AcpiUtReleaseWriteLock
174  *
175  * PARAMETERS:  Lock                - Pointer to a valid RW lock
176  *
177  * RETURN:      Status
178  *
179  * DESCRIPTION: Writer interfaces for reader/writer locks. Simply acquire or
180  *              release the writer mutex associated with the lock. Acquisition
181  *              of the lock is fully exclusive and will block all readers and
182  *              writers until it is released.
183  *
184  ******************************************************************************/
185 
186 ACPI_STATUS
187 AcpiUtAcquireWriteLock (
188     ACPI_RW_LOCK            *Lock)
189 {
190     ACPI_STATUS             Status;
191 
192 
193     Status = AcpiOsAcquireMutex (Lock->WriterMutex, ACPI_WAIT_FOREVER);
194     return (Status);
195 }
196 
197 
198 void
199 AcpiUtReleaseWriteLock (
200     ACPI_RW_LOCK            *Lock)
201 {
202 
203     AcpiOsReleaseMutex (Lock->WriterMutex);
204 }
205