src/common/SynchronizedConfig.h

/***************************************************************************
 *                                                                         *
 *   Copyright (C) 2006-2008 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(&flag, 0);
                        atomicSet(&lock, 0);
                    }

                    Reader(SynchronizedConfig& config);
                    ~Reader();
                private:
                    friend class SynchronizedConfig;
                    SynchronizedConfig& parent;
                    atomic_t lock;
                    atomic_t flag;
                    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++) {
            atomicSet(&(*iter)->flag, 1);
            if (atomicRead(&(*iter)->lock) && atomicRead(&(*iter)->flag)) {
                (*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) && atomicRead(&p->flag)) 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	persson	840	/***************************************************************************
2			* *
3	persson	1644	* Copyright (C) 2006-2008 Andreas Persson *
4	persson	840	* *
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	persson	846	#include <set>
25	persson	840
26			namespace LinuxSampler {
27
28			/**
29			* Thread safe management of configuration data, where the data is
30	persson	846	* updated by a single non real time thread and read by a number
31			* of real time threads.
32	persson	840	*
33			* The synchronization is achieved by using two instances of the
34			* configuration data. The non real time thread gets access to the
35	persson	846	* instance not currently in use by the real time threads by
36	persson	840	* 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	persson	846	* The real time threads need one Reader object each to access the
42	persson	1038	* 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	persson	846	* reading the data. (Neither Lock nor Unlock will block the real
46			* time thread, or use any system calls.)
47	persson	840	*/
48			template<class T>
49			class SynchronizedConfig {
50	schoenebeck	1424	struct atomic_t { volatile int word; };
51
52	persson	840	public:
53			SynchronizedConfig();
54
55			// methods for the real time thread
56
57	persson	846	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	schoenebeck	1424	atomicSet(&lock, 1);
70			return parent.config[atomicRead(&parent.indexAtomic)];
71	persson	846	}
72	persson	840
73	persson	846	/**
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	persson	1644	atomicSet(&flag, 0);
83	schoenebeck	1424	atomicSet(&lock, 0);
84	persson	846	}
85	persson	840
86	persson	846	Reader(SynchronizedConfig& config);
87			~Reader();
88			private:
89			friend class SynchronizedConfig;
90			SynchronizedConfig& parent;
91			atomic_t lock;
92	persson	1644	atomic_t flag;
93	persson	846	Reader *next; // only used locally in SwitchConfig
94			};
95	persson	840
96	persson	846
97	persson	840	// methods for the non real time thread
98
99			/**
100			* Gets the configuration object for use by the non real
101			* time thread. The object returned is not in use by the
102			* real time thread, so it can safely be updated. After
103			* the update is done, the non real time thread must call
104			* SwitchConfig() and the same update must be done again.
105			*
106			* @returns a reference to the configuration object to be
107			* updated by the non real time thread
108			*/
109			T& GetConfigForUpdate();
110
111			/**
112			* Atomically switch the newly updated configuration
113			* object with the one used by the real time thread, then
114			* wait for the real time thread to finish working with
115			* the old object before returning the old object.
116			* SwitchConfig() must be called by the non real time
117			* thread after an update has been done, and the object
118			* returned must be updated in the same way as the first.
119			*
120			* @returns a reference to the configuration object to be
121			* updated by the non real time thread
122			*/
123			T& SwitchConfig();
124
125			private:
126			atomic_t indexAtomic;
127			int updateIndex;
128			T config[2];
129	persson	846	std::set<Reader*> readers;
130	schoenebeck	1424
131			static int atomicRead(atomic_t* pSharedVariable) {
132			return pSharedVariable->word;
133			}
134
135			static void atomicSet(atomic_t* pSharedVariable, int value) {
136			pSharedVariable->word = value;
137			}
138	persson	840	};
139
140			template<class T> SynchronizedConfig<T>::SynchronizedConfig() {
141	schoenebeck	1424	atomicSet(&indexAtomic, 0);
142	persson	846	updateIndex = 1;
143	persson	840	}
144
145			template<class T> T& SynchronizedConfig<T>::GetConfigForUpdate() {
146			return config[updateIndex];
147			}
148
149			template<class T> T& SynchronizedConfig<T>::SwitchConfig() {
150	schoenebeck	1424	atomicSet(&indexAtomic, updateIndex);
151	persson	846
152			// first put all locking readers in a linked list
153			Reader* lockingReaders = 0;
154			for (typename std::set<Reader*>::iterator iter = readers.begin() ;
155			iter != readers.end() ;
156			iter++) {
157	persson	1644	atomicSet(&(*iter)->flag, 1);
158			if (atomicRead(&(iter)->lock) && atomicRead(&(iter)->flag)) {
159	persson	846	(*iter)->next = lockingReaders;
160			lockingReaders = *iter;
161			}
162			}
163
164			// wait until there are no locking readers left
165			while (lockingReaders) {
166	persson	840	usleep(50000);
167	persson	846	Reader** prev = &lockingReaders;
168			for (Reader* p = lockingReaders ; p ; p = p->next) {
169	persson	1644	if (atomicRead(&p->lock) && atomicRead(&p->flag)) prev = &p->next;
170	persson	846	else *prev = p->next; // unlink
171			}
172			}
173
174			updateIndex ^= 1;
175			return config[updateIndex];
176	persson	840	}
177
178	persson	846
179			// ----- Reader ----
180
181			template <class T>
182			SynchronizedConfig<T>::Reader::Reader(SynchronizedConfig& config) : parent(config) {
183	schoenebeck	1424	atomicSet(&lock, 0);
184	persson	846	parent.readers.insert(this);
185			}
186
187			template <class T>
188			SynchronizedConfig<T>::Reader::~Reader() {
189			parent.readers.erase(this);
190			}
191
192	persson	840	} // namespace LinuxSampler
193
194			#endif