|CONDITION(5)||Standards, Environments, and Macros||CONDITION(5)|
A condition variable enables threads to atomically block and test the condition under the protection of a mutual exclusion lock (mutex) until the condition is satisfied. If the condition is false, a thread blocks on a condition variable and atomically releases the mutex that is waiting for the condition to change. If another thread changes the condition, it may wake up waiting threads by signaling the associated condition variable. The waiting threads, upon awakening, reacquire the mutex and re-evaluate the condition.
The scope of a condition variable is either intra-process or inter-process. This is dependent upon whether the argument is passed implicitly or explicitly to the initialization of that condition variable. A condition variable does not need to be explicitly initialized. A condition variable is initialized with all zeros, by default, and its scope is set to within the calling process. For inter-process synchronization, a condition variable must be initialized once, and only once, before use.
A condition variable must not be simultaneously initialized by multiple threads or re-initialized while in use by other threads.
Condition variables attributes may be set to the default or customized at initialization. POSIX threads even allow the default values to be customized. Establishing these attributes varies depending upon whether POSIX or Solaris threads are used. Similar to the distinctions between POSIX and Solaris thread creation, POSIX condition variables implement the default, intra-process, unless an attribute object is modified for inter-process prior to the initialization of the condition variable. Solaris condition variables also implement as the default, intra-process; however, they set this attribute according to the argument, type, passed to their initialization function.
|ATTRIBUTE TYPE||ATTRIBUTE VALUE|
USYNC_THREAD does not support multiple mappings to the same logical synch object. If you need to mmap() a synch object to different locations within the same address space, then the synch object should be initialized as a shared object USYNC_PROCESS for Solaris, and PTHREAD_PROCESS_PRIVATE for POSIX.
|May 16, 2020|