src/common/SynchronizedConfig.h

/***************************************************************************
 *                                                                         *
 *   Copyright (C) 2006 Andreas Persson                                    *
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 *   This program is distributed in the hope that it will be useful,       *
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
 *   GNU General Public License for more details.                          *
 *                                                                         *
 *   You should have received a copy of the GNU General Public License     *
 *   along with this program; if not, write to the Free Software           *
 *   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,                *
 *   MA  02110-1301  USA                                                   *
 ***************************************************************************/

#ifndef __SYNCHRONIZEDCONFIG_H__
#define __SYNCHRONIZEDCONFIG_H__

#include "atomic.h"
#include <set>

namespace LinuxSampler {

    /**
     * Thread safe management of configuration data, where the data is
     * updated by a single non real time thread and read by a number
     * of real time threads.
     *
     * The synchronization is achieved by using two instances of the
     * configuration data. The non real time thread gets access to the
     * instance not currently in use by the real time threads by
     * calling GetConfigForUpdate(). After the data is updated, the
     * non real time thread must call SwitchConfig() and redo the
     * update on the other instance. SwitchConfig() blocks until it is
     * safe to modify the other instance.
     *
     * The real time threads need one Reader object each to access the
     * configuration data. This object must be created outside the
     * real time thread. The Lock() function returns a reference to
     * the data to be read, and Unlock() must be called when finished
     * reading the data. (Neither Lock nor Unlock will block the real
     * time thread, or use any system calls.)
     */
    template<class T>
    class SynchronizedConfig {
        public:
            SynchronizedConfig();

            // methods for the real time thread

            class Reader {
                public:
                    /**
                     * Gets the configuration object for use by the
                     * real time thread. The object is safe to use
                     * (read only) until Unlock() is called.
                     *
                     * @returns a reference to the configuration
                     *          object to be read by the real time
                     *          thread
                     */
                    const T& Lock() {
                        atomic_set(&lock, 1);
                        return parent.config[atomic_read(&parent.indexAtomic)];
                    }

                    /**
                     * Unlock the configuration object. Unlock() must
                     * be called by the real time thread after it has
                     * finished reading the configuration object. If
                     * the non real time thread is waiting in
                     * SwitchConfig() it will be awaken when no real
                     * time threads are locked anymore.
                     */
                    void Unlock() {
                        atomic_set(&lock, 0);
                    }

                    Reader(SynchronizedConfig& config);
                    ~Reader();
                private:
                    friend class SynchronizedConfig;
                    SynchronizedConfig& parent;
                    atomic_t lock;
                    Reader *next; // only used locally in SwitchConfig
            };


            // methods for the non real time thread

            /**
             * Gets the configuration object for use by the non real
             * time thread. The object returned is not in use by the
             * real time thread, so it can safely be updated. After
             * the update is done, the non real time thread must call
             * SwitchConfig() and the same update must be done again.
             *
             * @returns a reference to the configuration object to be
             *          updated by the non real time thread
             */
            T& GetConfigForUpdate();

            /**
             * Atomically switch the newly updated configuration
             * object with the one used by the real time thread, then
             * wait for the real time thread to finish working with
             * the old object before returning the old object.
             * SwitchConfig() must be called by the non real time
             * thread after an update has been done, and the object
             * returned must be updated in the same way as the first.
             *
             * @returns a reference to the configuration object to be
             *          updated by the non real time thread
             */
            T& SwitchConfig();

        private:
            atomic_t indexAtomic;
            int updateIndex;
            T config[2];
            std::set<Reader*> readers;
    };

    template<class T> SynchronizedConfig<T>::SynchronizedConfig() {
        atomic_set(&indexAtomic, 0);
        updateIndex = 1;
    }

    template<class T> T& SynchronizedConfig<T>::GetConfigForUpdate() {
        return config[updateIndex];
    }

    template<class T> T& SynchronizedConfig<T>::SwitchConfig() {
        atomic_set(&indexAtomic, updateIndex);

        // first put all locking readers in a linked list
        Reader* lockingReaders = 0;
        for (typename std::set<Reader*>::iterator iter = readers.begin() ;
             iter != readers.end() ;
             iter++) {
            if (atomic_read(&(*iter)->lock)) {
                (*iter)->next = lockingReaders;
                lockingReaders = *iter;
            }
        }

        // wait until there are no locking readers left
        while (lockingReaders) {
            usleep(50000);
            Reader** prev = &lockingReaders;
            for (Reader* p = lockingReaders ; p ; p = p->next) {
                if (atomic_read(&p->lock)) prev = &p->next;
                else *prev = p->next; // unlink
            }
        }

        updateIndex ^= 1;
        return config[updateIndex];
    }


    // ----- Reader ----

    template <class T>
    SynchronizedConfig<T>::Reader::Reader(SynchronizedConfig& config) : parent(config) {
        atomic_set(&lock, 0);
        parent.readers.insert(this);
    }

    template <class T>
    SynchronizedConfig<T>::Reader::~Reader() {
        parent.readers.erase(this);
    }

} // namespace LinuxSampler

#endif
1	/***************************************************************************
2	* *
3	* Copyright (C) 2006 Andreas Persson *
4	* *
5	* This program is free software; you can redistribute it and/or modify *
6	* it under the terms of the GNU General Public License as published by *
7	* the Free Software Foundation; either version 2 of the License, or *
8	* (at your option) any later version. *
9	* *
10	* This program is distributed in the hope that it will be useful, *
11	* but WITHOUT ANY WARRANTY; without even the implied warranty of *
12	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
13	* GNU General Public License for more details. *
14	* *
15	* You should have received a copy of the GNU General Public License *
16	* along with this program; if not, write to the Free Software *
17	* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, *
18	* MA 02110-1301 USA *
19	***************************************************************************/
20
21	#ifndef __SYNCHRONIZEDCONFIG_H__
22	#define __SYNCHRONIZEDCONFIG_H__
23
24	#include "atomic.h"
25	#include <set>
26
27	namespace LinuxSampler {
28
29	/**
30	* Thread safe management of configuration data, where the data is
31	* updated by a single non real time thread and read by a number
32	* of real time threads.
33	*
34	* The synchronization is achieved by using two instances of the
35	* configuration data. The non real time thread gets access to the
36	* instance not currently in use by the real time threads by
37	* calling GetConfigForUpdate(). After the data is updated, the
38	* non real time thread must call SwitchConfig() and redo the
39	* update on the other instance. SwitchConfig() blocks until it is
40	* safe to modify the other instance.
41	*
42	* The real time threads need one Reader object each to access the
43	* configuration data. This object must be created outside the
44	* real time thread. The Lock() function returns a reference to
45	* the data to be read, and Unlock() must be called when finished
46	* reading the data. (Neither Lock nor Unlock will block the real
47	* time thread, or use any system calls.)
48	*/
49	template<class T>
50	class SynchronizedConfig {
51	public:
52	SynchronizedConfig();
53
54	// methods for the real time thread
55
56	class Reader {
57	public:
58	/**
59	* Gets the configuration object for use by the
60	* real time thread. The object is safe to use
61	* (read only) until Unlock() is called.
62	*
63	* @returns a reference to the configuration
64	* object to be read by the real time
65	* thread
66	*/
67	const T& Lock() {
68	atomic_set(&lock, 1);
69	return parent.config[atomic_read(&parent.indexAtomic)];
70	}
71
72	/**
73	* Unlock the configuration object. Unlock() must
74	* be called by the real time thread after it has
75	* finished reading the configuration object. If
76	* the non real time thread is waiting in
77	* SwitchConfig() it will be awaken when no real
78	* time threads are locked anymore.
79	*/
80	void Unlock() {
81	atomic_set(&lock, 0);
82	}
83
84	Reader(SynchronizedConfig& config);
85	~Reader();
86	private:
87	friend class SynchronizedConfig;
88	SynchronizedConfig& parent;
89	atomic_t lock;
90	Reader *next; // only used locally in SwitchConfig
91	};
92
93
94	// methods for the non real time thread
95
96	/**
97	* Gets the configuration object for use by the non real
98	* time thread. The object returned is not in use by the
99	* real time thread, so it can safely be updated. After
100	* the update is done, the non real time thread must call
101	* SwitchConfig() and the same update must be done again.
102	*
103	* @returns a reference to the configuration object to be
104	* updated by the non real time thread
105	*/
106	T& GetConfigForUpdate();
107
108	/**
109	* Atomically switch the newly updated configuration
110	* object with the one used by the real time thread, then
111	* wait for the real time thread to finish working with
112	* the old object before returning the old object.
113	* SwitchConfig() must be called by the non real time
114	* thread after an update has been done, and the object
115	* returned must be updated in the same way as the first.
116	*
117	* @returns a reference to the configuration object to be
118	* updated by the non real time thread
119	*/
120	T& SwitchConfig();
121
122	private:
123	atomic_t indexAtomic;
124	int updateIndex;
125	T config[2];
126	std::set<Reader*> readers;
127	};
128
129	template<class T> SynchronizedConfig<T>::SynchronizedConfig() {
130	atomic_set(&indexAtomic, 0);
131	updateIndex = 1;
132	}
133
134	template<class T> T& SynchronizedConfig<T>::GetConfigForUpdate() {
135	return config[updateIndex];
136	}
137
138	template<class T> T& SynchronizedConfig<T>::SwitchConfig() {
139	atomic_set(&indexAtomic, updateIndex);
140
141	// first put all locking readers in a linked list
142	Reader* lockingReaders = 0;
143	for (typename std::set<Reader*>::iterator iter = readers.begin() ;
144	iter != readers.end() ;
145	iter++) {
146	if (atomic_read(&(*iter)->lock)) {
147	(*iter)->next = lockingReaders;
148	lockingReaders = *iter;
149	}
150	}
151
152	// wait until there are no locking readers left
153	while (lockingReaders) {
154	usleep(50000);
155	Reader** prev = &lockingReaders;
156	for (Reader* p = lockingReaders ; p ; p = p->next) {
157	if (atomic_read(&p->lock)) prev = &p->next;
158	else *prev = p->next; // unlink
159	}
160	}
161
162	updateIndex ^= 1;
163	return config[updateIndex];
164	}
165
166
167	// ----- Reader ----
168
169	template <class T>
170	SynchronizedConfig<T>::Reader::Reader(SynchronizedConfig& config) : parent(config) {
171	atomic_set(&lock, 0);
172	parent.readers.insert(this);
173	}
174
175	template <class T>
176	SynchronizedConfig<T>::Reader::~Reader() {
177	parent.readers.erase(this);
178	}
179
180	} // namespace LinuxSampler
181
182	#endif