src/common/SynchronizedConfig.h

/***************************************************************************
 *                                                                         *
 *   Copyright (C) 2006, 2007 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 <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 {
        struct atomic_t { volatile int word; };

        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() {
                        atomicSet(&lock, 1);
                        return parent.config[atomicRead(&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() {
                        atomicSet(&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;

            static int atomicRead(atomic_t* pSharedVariable) {
                return pSharedVariable->word;
            }

            static void atomicSet(atomic_t* pSharedVariable, int value) {
                pSharedVariable->word = value;
            }
    };

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

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

    template<class T> T& SynchronizedConfig<T>::SwitchConfig() {
        atomicSet(&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 (atomicRead(&(*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 (atomicRead(&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) {
        atomicSet(&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, 2007 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 <set>
25
26	namespace LinuxSampler {
27
28	/**
29	* Thread safe management of configuration data, where the data is
30	* updated by a single non real time thread and read by a number
31	* of real time threads.
32	*
33	* The synchronization is achieved by using two instances of the
34	* configuration data. The non real time thread gets access to the
35	* instance not currently in use by the real time threads by
36	* calling GetConfigForUpdate(). After the data is updated, the
37	* non real time thread must call SwitchConfig() and redo the
38	* update on the other instance. SwitchConfig() blocks until it is
39	* safe to modify the other instance.
40	*
41	* The real time threads need one Reader object each to access the
42	* configuration data. This object must be created outside the
43	* real time thread. The Lock() function returns a reference to
44	* the data to be read, and Unlock() must be called when finished
45	* reading the data. (Neither Lock nor Unlock will block the real
46	* time thread, or use any system calls.)
47	*/
48	template<class T>
49	class SynchronizedConfig {
50	struct atomic_t { volatile int word; };
51
52	public:
53	SynchronizedConfig();
54
55	// methods for the real time thread
56
57	class Reader {
58	public:
59	/**
60	* Gets the configuration object for use by the
61	* real time thread. The object is safe to use
62	* (read only) until Unlock() is called.
63	*
64	* @returns a reference to the configuration
65	* object to be read by the real time
66	* thread
67	*/
68	const T& Lock() {
69	atomicSet(&lock, 1);
70	return parent.config[atomicRead(&parent.indexAtomic)];
71	}
72
73	/**
74	* Unlock the configuration object. Unlock() must
75	* be called by the real time thread after it has
76	* finished reading the configuration object. If
77	* the non real time thread is waiting in
78	* SwitchConfig() it will be awaken when no real
79	* time threads are locked anymore.
80	*/
81	void Unlock() {
82	atomicSet(&lock, 0);
83	}
84
85	Reader(SynchronizedConfig& config);
86	~Reader();
87	private:
88	friend class SynchronizedConfig;
89	SynchronizedConfig& parent;
90	atomic_t lock;
91	Reader *next; // only used locally in SwitchConfig
92	};
93
94
95	// methods for the non real time thread
96
97	/**
98	* Gets the configuration object for use by the non real
99	* time thread. The object returned is not in use by the
100	* real time thread, so it can safely be updated. After
101	* the update is done, the non real time thread must call
102	* SwitchConfig() and the same update must be done again.
103	*
104	* @returns a reference to the configuration object to be
105	* updated by the non real time thread
106	*/
107	T& GetConfigForUpdate();
108
109	/**
110	* Atomically switch the newly updated configuration
111	* object with the one used by the real time thread, then
112	* wait for the real time thread to finish working with
113	* the old object before returning the old object.
114	* SwitchConfig() must be called by the non real time
115	* thread after an update has been done, and the object
116	* returned must be updated in the same way as the first.
117	*
118	* @returns a reference to the configuration object to be
119	* updated by the non real time thread
120	*/
121	T& SwitchConfig();
122
123	private:
124	atomic_t indexAtomic;
125	int updateIndex;
126	T config[2];
127	std::set<Reader*> readers;
128
129	static int atomicRead(atomic_t* pSharedVariable) {
130	return pSharedVariable->word;
131	}
132
133	static void atomicSet(atomic_t* pSharedVariable, int value) {
134	pSharedVariable->word = value;
135	}
136	};
137
138	template<class T> SynchronizedConfig<T>::SynchronizedConfig() {
139	atomicSet(&indexAtomic, 0);
140	updateIndex = 1;
141	}
142
143	template<class T> T& SynchronizedConfig<T>::GetConfigForUpdate() {
144	return config[updateIndex];
145	}
146
147	template<class T> T& SynchronizedConfig<T>::SwitchConfig() {
148	atomicSet(&indexAtomic, updateIndex);
149
150	// first put all locking readers in a linked list
151	Reader* lockingReaders = 0;
152	for (typename std::set<Reader*>::iterator iter = readers.begin() ;
153	iter != readers.end() ;
154	iter++) {
155	if (atomicRead(&(*iter)->lock)) {
156	(*iter)->next = lockingReaders;
157	lockingReaders = *iter;
158	}
159	}
160
161	// wait until there are no locking readers left
162	while (lockingReaders) {
163	usleep(50000);
164	Reader** prev = &lockingReaders;
165	for (Reader* p = lockingReaders ; p ; p = p->next) {
166	if (atomicRead(&p->lock)) prev = &p->next;
167	else *prev = p->next; // unlink
168	}
169	}
170
171	updateIndex ^= 1;
172	return config[updateIndex];
173	}
174
175
176	// ----- Reader ----
177
178	template <class T>
179	SynchronizedConfig<T>::Reader::Reader(SynchronizedConfig& config) : parent(config) {
180	atomicSet(&lock, 0);
181	parent.readers.insert(this);
182	}
183
184	template <class T>
185	SynchronizedConfig<T>::Reader::~Reader() {
186	parent.readers.erase(this);
187	}
188
189	} // namespace LinuxSampler
190
191	#endif