Updated: October 28, 2024 |
Safely set bits in a variable, returning the previous value (QNX Neutrino)
#include <atomic.h> unsigned atomic_set_value( volatile unsigned * loc, unsigned bits );
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The atomic_set_value() function is a thread-safe way of doing an (*loc) |= bits 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.
The implementation of atomic functions may depend on the architecture. For more information, see LL/SC vs LSE atomic operations in the description in Building Embedded Systems of the cpuinfo area of the system page.
The previous value at loc.
To safely set the 1 bit in a flag:
#include <atomic.h> … volatile unsigned flags; unsigned previous; … previous = atomic_set_value( &flags, 0x01 );
Safety: | |
---|---|
Cancellation point | No |
Interrupt handler | Yes |
Signal handler | Yes |
Thread | Yes |