fetch_and_add Kernel Services
Purpose
Increments a variable atomically.
Syntax
Parameters
| Item | Description |
|---|---|
| addr | Specifies the address of the variable to be incremented. |
| value | Specifies the value to be added to the variable. |
Description
The fetch_and_add kernel services atomically increment a variable.
The fetch_and_add kernel service operates on a single word (32 bit) variable while the fetch_and_addlp kernel service operates on a double word (64 bit) variable.
These operations are useful when a counter variable is shared between several kernel threads, because it ensures that the fetch, update, and store operations used to increment the counter occur atomically (are not interruptible).
Note:
- The single word variable for the fetch_and_add kernel service must be aligned on a word (32 bit) boundary.
- The double word variable for the fetch_and_addlp kernel service must be aligned on a double word (64 bit) boundary.
Execution Environment
The fetch_and_add kernel services can be called from either the process or interrupt environment.
Return Values
The fetch_and_add kernel services return the original value of the variable.