Safely add to a variable (QNX Neutrino)
#include <atomic.h> void atomic_add( volatile unsigned * loc, unsigned incr );
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The atomic_add() function is a thread-safe way of doing an (*loc) += incr operation.
When modifying a variable shared between a thread and an interrupt handler, you must either disable interrupts or use atomic operations.
The atomic_*() functions are also useful for modifying variables that are referenced by more than one thread (that aren't necessarily in the same process) without having to use a mutex.
To safely increment a counter shared between multiple threads:
#include <atomic.h> … volatile unsigned count; … atomic_add( &count, 1 );
Safety: | |
---|---|
Cancellation point | No |
Interrupt handler | Yes |
Signal handler | Yes |
Thread | Yes |