KMD_KMSema

kmd

1998 12-06

CLASS

SYNOPSIS

PARENTS

CONSTRUCTOR

KMD_KMSema()
Call KMD_KMSema(KMD_Ident *out_key) with a dummy KMD_Ident.
KMD_KMSema(KMD_Ident *out_key)
Create a new KMD_KMSema resource.
KMD_KMSema(KMD_Ident in_key)
Use an existing KMD_KMSema as identified by in_key.

MEMBER FUNCTIONS

uint32 Semop(long *count, char wait, char comparator, int operand, char set_method, int set_value, char undo_method, int undo_value)
Do a semaphore operation. The argument count returns the semaphore value after the operation. If wait is TRUE then the call will wait until the operation is completed. Otherwise, the call will return even if the operation was not completed. The comparator specifies what type of comparison to do to determine whether or not to do the operation. The possible comparators are:


KMSEM_EQ	TRUE if count == operand
KMSEM_LT	TRUE if count < operand
KMSEM_GT	TRUE if count > operand
KMSEM_LE	TRUE if count <= operand
KMSEM_GE	TRUE if count >= operand
KMSEM_NE	TRUE if count != operand

The operation to do when the comparator is TRUE is specified by set_method and set_value. The possible methods are:


KMSEM_REL	increase the count by set_value
KMSEM_ABS	set the count to set_value

Note that set_value may be negative. When a process dies while holding a handle to a semaphore the keymaster may adjust the value of the semaphore. The undo_method and undo_value arguments specify this adjustment. For example, if a semaphore is being used to count how many processes are using a resource the 'get resource' operation may be KMSEM_REL and 1 with an undo of KMSEM_REL and -1. When the process stops using the resource the operation may be KMSEM_REL and -1 with an undo of KMSEM_REL and 0.