source: lib/data-struct/message_queue.c @ ee6e802

4.0.1-hotfixescachetimestampsdevelopdpdk-ndagetsilivendag_formatrc-4.0.1rc-4.0.2rc-4.0.3rc-4.0.4ringdecrementfixringperformanceringtimestampfixes
Last change on this file since ee6e802 was ee6e802, checked in by Shane Alcock <salcock@…>, 4 years ago

Updated copyright blurb on all source files

In some cases, this meant adding copyright blurbs to files that
had never had them before.

  • Property mode set to 100644
File size: 5.5 KB
Line 
1/*
2 *
3 * Copyright (c) 2007-2016 The University of Waikato, Hamilton, New Zealand.
4 * All rights reserved.
5 *
6 * This file is part of libtrace.
7 *
8 * This code has been developed by the University of Waikato WAND
9 * research group. For further information please see http://www.wand.net.nz/
10 *
11 * libtrace is free software; you can redistribute it and/or modify
12 * it under the terms of the GNU Lesser General Public License as published by
13 * the Free Software Foundation; either version 3 of the License, or
14 * (at your option) any later version.
15 *
16 * libtrace is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
19 * GNU Lesser General Public License for more details.
20 *
21 * You should have received a copy of the GNU Lesser General Public License
22 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
23 *
24 *
25 */
26#include "message_queue.h"
27
28#include <unistd.h>
29#include <stdio.h>
30#include <limits.h>
31#include <assert.h>
32
33/**
34 * TODO look into using eventfd instead of a pipe if we have it available XXX
35 */
36
37/**
38 * @param mq A pointer to allocated space for a libtrace message queue
39 * @param message_len The size in bytes of the message item, to ensure thread safety this
40 *                should be less than PIPE_BUF (normally at least 512bytes)
41 *                see: man 7 pipe notes on atomic operations
42 */
43void libtrace_message_queue_init(libtrace_message_queue_t *mq, size_t message_len)
44{
45        assert(message_len);
46        ASSERT_RET(pipe(mq->pipefd), != -1);
47        mq->message_count = 0;
48        if (message_len > PIPE_BUF)
49                fprintf(stderr, "Warning message queue wont be atomic (thread safe) message_len(%zu) > PIPE_BUF(%d)\n",
50                                        message_len, PIPE_BUF);
51        mq->message_len = message_len;
52        pthread_spin_init(&mq->spin, 0);
53}
54
55/**
56 * Posts a message to the given message queue.
57 *
58 * This will block if a reader is not keeping up and the underlying pipe
59 * fills up.
60 *
61 * @param mq A pointer to a initilised libtrace message queue structure (NOT NULL)
62 * @param message A pointer to the message data you wish to send
63 * @return A number representing the number of messages already in the queue,
64 *         0 implies a thread was waiting and will read your message, negative
65 *         numbers implies threads are still waiting. Positive implies a backlog
66 *         of messages.
67 */
68int libtrace_message_queue_put(libtrace_message_queue_t *mq, const void *message)
69{
70        int ret;
71        assert(mq->message_len);
72        ASSERT_RET(write(mq->pipefd[1], message, mq->message_len), == (int) mq->message_len);
73        // Update after we've written
74        pthread_spin_lock(&mq->spin);
75        ret = ++mq->message_count; // Should be CAS!
76        pthread_spin_unlock(&mq->spin);
77        return ret;
78}
79
80/**
81 * Retrieves a message from the given message queue.
82 *
83 * This will block if a reader is not keeping up and the underlying pipe
84 * fills up.
85 *
86 * @param mq A pointer to a initilised libtrace message queue structure (NOT NULL)
87 * @param message A pointer to the message data you wish to send
88 * @return The number of messages remaining in the queue less any threads waiting,
89 *         0 implies a thread was waiting and will read your message, negative
90 *         numbers implies threads are still waiting. Positive implies a backlog
91 *         of messages.
92 */
93int libtrace_message_queue_get(libtrace_message_queue_t *mq, void *message)
94{
95        int ret;
96        // Safely decrease count first - Yes this might make us negative, however thats ok once a write comes in everything will be fine
97        pthread_spin_lock(&mq->spin);
98        ret = mq->message_count--;
99        pthread_spin_unlock(&mq->spin);
100        ASSERT_RET(read(mq->pipefd[0], message, mq->message_len), == (int) mq->message_len);
101        return ret;
102}
103
104/**
105 * Trys to retrieve a message from the given message queue.
106 *
107 * This will not block and instead returns LIBTRACE_MQ_FAILED if
108 * no message is available.
109 *
110 * @param mq A pointer to a initilised libtrace message queue structure (NOT NULL)
111 * @param message A pointer to the message data you wish to send
112 * @return The number of messages remaining in the queue less any threads waiting,
113 *         0 implies a thread was waiting and will read your message, negative
114 *         numbers implies threads are still waiting. Positive implies a backlog
115 *         of messages.
116 */
117int libtrace_message_queue_try_get(libtrace_message_queue_t *mq, void *message)
118{
119        int ret;
120        // Safely decrease count first - Yes this might make us negative, however thats ok once a write comes in everything will be fine
121        // ->Fast path avoid the lock
122        if (mq->message_count <= 0)
123                return LIBTRACE_MQ_FAILED;
124        // Else grab lock and confirm this is so
125        pthread_spin_lock(&mq->spin);
126        if (mq->message_count > 0) {
127                ret = --mq->message_count;
128                // :( read(...) needs to be done within the *spin* lock otherwise blocking might steal our read
129                ASSERT_RET(read(mq->pipefd[0], message, mq->message_len), == (int) mq->message_len);
130        } else {
131                ret = LIBTRACE_MQ_FAILED;
132        }
133        pthread_spin_unlock(&mq->spin);
134        return ret;
135}
136
137/**
138 * May be negative if threads blocking and waiting for a message.
139 */
140int libtrace_message_queue_count(const libtrace_message_queue_t *mq)
141{
142        // This is only ok because we know int is atomic
143        return mq->message_count;
144}
145
146void libtrace_message_queue_destroy(libtrace_message_queue_t *mq)
147{
148        mq->message_count = 0;
149        mq->message_len = 0;
150        close(mq->pipefd[0]);
151        close(mq->pipefd[1]);
152        pthread_spin_destroy(&mq->spin);
153}
154
155/**
156 * @return a file descriptor for the queue, can be used with select() poll() etc.
157 */
158int libtrace_message_queue_get_fd(libtrace_message_queue_t *mq)
159{
160        return mq->pipefd[0];
161}
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