Synchronization services

The QNX Neutrino RTOS provides the POSIX-standard thread-level synchronization primitives, some of which are useful even between threads in different processes.

The synchronization services include at least the following:

Synchronization service	Supported between processes	Supported across a QNX Neutrino LAN
Mutexes	Yes^a	No
Condvars	Yes	No
Barriers	Yes^a	No
Sleepon locks	No	No
Reader/writer locks	Yes^a	No
Semaphores	Yes	Yes (named only)
FIFO scheduling	Yes	No
Send/Receive/Reply	Yes	Yes
Atomic operations	Yes	No

^a Sharing this type of object between processes can be a security problem; see “Safely sharing mutexes, barriers, and reader/writer locks between processes,” later in this chapter.

The above synchronization primitives are implemented directly by the kernel, except for:

barriers, sleepon locks, and reader/writer locks (which are built from mutexes and condvars)
atomic operations (which are either implemented directly by the processor or emulated in the kernel)

Note: You should allocate mutexes, condvars, barriers, reader/writer locks, and semaphores, as well as objects you plan to use atomic operations on, only in normal memory mappings. On certain processors, atomic operations and calls such as pthread_mutex_lock() will cause a fault if the object is allocated in uncached memory.