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| -rw-r--r-- | include/asterisk/lock.h | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/include/asterisk/lock.h b/include/asterisk/lock.h index 53c56a544..2253a455b 100644 --- a/include/asterisk/lock.h +++ b/include/asterisk/lock.h @@ -18,6 +18,33 @@ /*! \file * \brief General Asterisk channel locking definitions. + * + * This file provides several different implementation of the functions, + * depending on the platform, the use of DEBUG_THREADS, and the way + * global mutexes are initialized. + * At the moment, we have 3 ways to initialize global mutexes, depending on + * + * + static: the mutex is assigned the value AST_MUTEX_INIT_VALUE + * this is done at compile time, and is the way used on Linux. + * This method is not applicable to all platforms e.g. when the + * initialization needs that some code is run. + * + * + on first use: the mutex is assigned a magic value at compile time, + * and ast_mutex_init() is called when this magic value is detected. + * This technique is generally applicable, though it has a bit of + * overhead on each access to check whether initialization is needed. + * On the other hand, the overall cost of a mutex_lock operation + * is such that this overhead is often negligible. + + * + through constructors: for each mutex, a constructor function is + * defined, which then runs when the program (or the module) + * starts. The problem with this approach is that there is a + * lot of code duplication (a new block of code is created for + * each mutex). Also, it does not prevent a user from declaring + * a global mutex without going through the wrapper macros, + * so sane programming practices are still required. + * + * Eventually we should converge on a single method for all platforms. */ #ifndef _ASTERISK_LOCK_H |