atomic_add()
Safely add to a variable (QNX Neutrino)
Synopsis:
#include <atomic.h>
void atomic_add( volatile unsigned * loc,
unsigned incr );
Arguments:
- loc
- A pointer to the location that you want to add a value to.
- incr
- The number that you want to add.
Library:
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
Description:
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.
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.
Examples:
To safely increment a counter shared between multiple threads:
#include <atomic.h>
…
volatile unsigned count;
…
atomic_add( &count, 1 );
Classification:
| Safety: | |
|---|---|
| Cancellation point | No |
| Interrupt handler | Yes |
| Signal handler | Yes |
| Thread | Yes |