개요

• 솔라나라에 설명된 어플리케이션에 대해 맨 페이지를 찾아 출력한다.
• MAN 페이지에 대한 설명은 윈디하나의 솔라나라: MAN 페이지을 참고하자.
• svcadm(8)을 검색하려면 섹션에서 8 을 선택하고, 맨 페이지 이름에 svcadm을 입력하고 검색을 누른다.

semaphore(9f)

semaphore(9F)                  Kernel Functions                  semaphore(9F)



NAME
       semaphore,   sema_init,   sema_destroy,   sema_p,  sema_p_sig,  sema_v,
       sema_tryp - semaphore functions

SYNOPSIS
       #include <sys/ksynch.h>

       void sema_init(ksema_t *sp, uint_t val, char *name, ksema_type_t type,
             void *arg);


       void sema_destroy(ksema_t *sp);


       void sema_p(ksema_t *sp);


       void sema_v(ksema_t *sp);


       int sema_p_sig(ksema_t *sp);


       int sema_tryp(ksema_t *sp);

INTERFACE LEVEL
       Solaris DDI specific (Solaris DDI).

PARAMETERS
       sp      A pointer to a semaphore, type ksema_t.


       val     Initial value for semaphore.


       name    Descriptive string. This is obsolete and should be NULL.  (Non-
               NULL strings are legal, but they are a waste of kernel memory.)


       type    Variant  type  of the semaphore. Currently, only SEMA_DRIVER is
               supported.


       arg     Type-specific argument; should be NULL.


DESCRIPTION
       These functions implement counting semaphores as described by Dijkstra.
       A semaphore has a value which is atomically decremented by sema_p() and
       atomically incremented by sema_v(). The value must  always  be  greater
       than or equal to zero. If sema_p() is called and the value is zero, the
       calling thread is blocked until  another  thread  performs  a  sema_v()
       operation on the semaphore.


       Semaphores  are  initialized by calling sema_init(). The argument, val,
       gives the initial value for the semaphore.  The  semaphore  storage  is
       provided by the caller but more may be dynamically allocated, if neces‐
       sary, by sema_init(). For this reason, sema_destroy() should be  called
       before deallocating the storage containing the semaphore.


       The  sema_p_sig()  function decrements the semaphore, as does sema_p().
       However, if the semaphore value is zero, sema_p_sig() will return with‐
       out decrementing the value if a signal (that is, from kill(2)) is pend‐
       ing for the thread.


       The sema_tryp() function will decrement the semaphore value only if  it
       is greater than zero, and will not block.

RETURN VALUES
       0    sema_tryp() could not decrement the semaphore value because it was
            zero.


       1    sema_p_sig() was not able to decrement  the  semaphore  value  and
            detected a pending signal.


CONTEXT
       These  functions can be called from user, interrupt, or kernel context,
       except for sema_init() and sema_destroy(), which  can  be  called  from
       user or kernel context only. None of these functions can be called from
       a high-level interrupt context. In most cases,  sema_v()  and  sema_p()
       should not be called from any interrupt context.


       If  sema_p()  is used from interrupt context, lower-priority interrupts
       will not be serviced during the wait. This means  that  if  the  thread
       that  will  eventually perform the sema_v() becomes blocked on anything
       that requires the lower-priority interrupt, the system will hang.


       For example, the thread that will perform  the  sema_v()  may  need  to
       first  allocate  memory. This memory allocation may require waiting for
       paging I/O to complete, which may require a lower-priority disk or net‐
       work  interrupt  to  be  serviced. In general, situations like this are
       hard to predict, so it is advisable to avoid waiting on  semaphores  or
       condition variables in an interrupt context.

SEE ALSO
       kill(2), condvar(9F), mutex(9F)


       Writing Device Drivers in Oracle Solaris 11.4



Oracle Solaris 11.4               16 Jan 2006                    semaphore(9F)