tstop Kernel Service
Purpose
Cancels a pending timer request.
Syntax
#include <sys/types.h>
#include <sys/errno.h>
#include <sys/timer.h>int tstop ( t)
struct trb *t;
struct trb *t;
Parameter
| Item | Description |
|---|---|
| t | Specifies the pending timer request to cancel. |
Description
The tstop kernel service cancels a pending timer request. The tstop kernel service must be called before a timer request block can be freed with the tfree kernel service.
In a multiprocessor environment, the timer function associated with a timer request block may be active on another processor when the tstop kernel service is called. In this case, the timer request cannot be canceled. A multiprocessor-safe driver must therefore check the return code and take appropriate action if the cancel request failed.
In a uniprocessor
environment, the call always succeeds. This is untrue in a multiprocessor
environment, where the call will fail if the timer is being handled
by another processor. Therefore, the function now has a return value,
which is set to 0 if successful, or -1 otherwise. Funnelled device
drivers do not need to check the return value since they run in a
logical uniprocessor environment. Multiprocessor-safe and multiprocessor-efficient
device drivers need to check the return value in a loop. In addition,
if a driver uses locking, it must release and reacquire its lock within
this loop. A delay should be used between the release and reacquiring
the lock as shown below:
while (tstop(&trp)) {
release_any_lock;
delay_some_time;
reacquire_the_lock;
} /* null while loop if locks not used */
Execution Environment
The tstop kernel service can be called from either the process or interrupt environment.
Return Values
| Item | Description |
|---|---|
| 0 | Indicates that the request was successfully canceled. |
| -1 | Indicates that the request could not be canceled. |