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# Miscellaneous Functions and Constants

Declared in: be/kernel/OS.h (unless otherwise noted)

## Functions

### clear_caches()

Declared in: be/kernel/image.h

void `clear_caches(`void *addr, size_t len, uint32 flags`)`

This function clears or invalidates the instruction and data caches. You should only need this function if you're generating code on the fly, or if you're performing a timing loop and you want to start with fresh caches (to get a "worst case" estimate).

The argument are:

- addr is the starting address of a section of memory that corresponds to a section of one of the caches.

- len is the length, in bytes, of the instruction or data segment that you want to clear or invalidate.

- flags is one or both of `B_INVALIDATE_ICACHE` and `B_FLUSH_DCACHE`.

By invalidating a section of the instruction cache, you cause the instructions in that section to be reloaded next time they're needed. Flushing the data cache causes the in-memory copy of the data to be written out to the cache.

### debugger()

void `debugger(`const char *string`)`

Throws the calling thread into the debugger. The string argument becomes the debugger's first utterance.

### disable_debugger()

int `disable_debugger(`int state`)`

Instructs the kernel to send a signal for all exceptions, even those that don't normally trigger the debugger. If the application doesn't have a handler installed for the exception, the team dies without triggering the debugger. state should be nonzero to turn on this functionality or 0 to turn it off.

### set_alarm()

bigtime_t `set_alarm(`bigtime_t time, uint32 mode`)`

Tells the kernel to send the `SIGALRM` signal at some point in the future, as defined by the arguments:

- If mode is `B_PERIODIC_ALARM`, the signal is sent every time microseconds, starting as soon as `set_alarm()` function returns.

- If mode is `B_ONE_SHOT_ABOLUTE_ALARM`, the signal is sent once (only) after time microseconds have elapsed measured from the time the system was booted. If that point has already passed, the signal is sent immediately.

- If mode is `B_ONE_SHOT_RELATIVE_ALARM`, the signal is sent once (only) after time microseconds have elapsed from the time `set_alarm()` returns.

When the signal is sent, the `SIGALRM` handler is called (you set the handler through the normal means, by calling the Posix `signal()` function). The handler runs in the thread that set the alarm.

| From within the `SIGALRM` handler, you mustn't call anything that would cause the kernel scheduler to run. Just about the only safe call you can make from your signal handler is `release_sem()`.

The most recent alarm requested cancels any previous request. For example, in this sequence...

       /* Ask for an alarm ten seconds from now. */
       set_alarm(10e6, B_ONE_SHOT_RELATIVE_ALARM);
       /* Ask for an alarm one second from now. */
       set_alarm(10e5, B_ONE_SHOT_RELATIVE_ALARM);

...only the second alarm request will be fulfilled—the first requested is cancelled when the second `set_alarm()` call is made. This applies to all alarm types; for example, a one-shot alarm request will cancel an active periodic alarm.

To explicitly cancel the previous alarm request without installing a new alarm, do this:

       set_alarm(B_INFINITE_TIMEOUT, B_PERIODIC_ALARM);

This cancels the previous alarm request regardless of the type of alarm.

### set_signal_stack()

Declared in: posix/signal.be.h

void `set_signal_stack(`void *ptr, size_t size`)`

Sets the location and size of the stack that's used by the thread's signal handlers.

## Constants

### B_INFINITE_TIMEOUT

`B_INFINITE_TIMEOUT`

The inifinite timeout value can be used to specify, to timeout-accepting functions, that you're willing to wait forever.

### B_OS_NAME_LENGTH

`B_OS_NAME_LENGTH`

This constant gives the maximum length of the name of a thread, semaphore, port, area, or other operating system bauble.

### B_PAGE_SIZE

`B_PAGE_SIZE`

The `B_PAGE_SIZE` constant gives the size, in bytes, of a page of RAM.

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