Safely subtract from a variable (QNX Neutrino)
#include <atomic.h> void atomic_sub( volatile unsigned * loc, unsigned decr );
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The atomic_sub() function is a thread-safe way of doing a (*loc) -= decr 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.
Safely subtract 1 from a counter:
#include <atomic.h> … volatile unsigned count; … atomic_sub( &count, 1 );
Safety: | |
---|---|
Cancellation point | No |
Interrupt handler | Yes |
Signal handler | Yes |
Thread | Yes |