SVR5

SV_WAIT(D3)

SV_WAIT -- block on a synchronization variable

Synopsis

   #include <sys/types.h>
   #include <sys/ksynch.h>
   #include <sys/ddi.h>
   
   void SV_WAIT(sv_t *svp, int priority, lock_t *lkp);

Description

SV_WAIT causes the calling process to block (the caller's execution is suspended and other processes may be scheduled) waiting for a call to SV_SIGNAL(D3) or SV_BROADCAST(D3) for the synchronization variable specified by svp.

Arguments

svp: Pointer to the synchronization variable on which to sleep.
priority: A hint to the scheduling policy as to the relative priority the caller wishes to be assigned while running in the kernel after waking up.
lkp: Pointer to a basic lock which must be locked when SV_WAIT is called. The basic lock is released when the calling process blocks, as described below.

Return values

None

Usage

priority argument

Valid values for priority are:

pridisk: Priority appropriate for disk driver.
prinet: Priority appropriate for network driver.
pritty: Priority appropriate for terminal driver.
pritape: Priority appropriate for tape driver.
prihi: High priority.
primed: Medium priority.
prilo: Low priority.

Drivers may use these values to request a priority appropriate to a given type of device or to request a priority that is high, medium or low relative to other activities within the kernel.

It is also permissible to specify positive or negative offsets from the values defined above. Positive offsets result in more favorable priority. The maximum allowable offset in all cases is 3 (that is, pridisk+3 and pridisk-3 are valid values but pridisk+4 and pridisk-4 are not valid). Offsets can be useful in defining the relative importance of different locks or resources that may be held by a given driver. In general, a higher relative priority should be used when the caller is blocked waiting for a highly contended kernel resource, or when the caller is already holding one or more locks or kernel resources upon entry to SV_WAIT.

The exact semantic of the priority argument is specific to the scheduling class of the caller, and some scheduling classes may choose to ignore the argument for the purposes of assigning a scheduling priority.

lkp argument

The basic lock specified by lkp must be held by the caller upon entry. The lock is released and the interrupt priority level is set to plbase (block no interrupts) after the process is queued on the synchronization variable but prior to context switching to another process. When the caller returns from SV_WAIT, the basic lock is not held and the interrupt priority level is equal to plbase.

General considerations

The caller will not be interrupted by signals while sleeping inside SV_WAIT.

Calls to SV_WAIT( ) must be able to tolerate premature wakeups. After it is awakened (unblocked), it must reexamine the condition on which it was blocked.

Context and synchronization

User or blockable context.

Hardware applicability

All

Version applicability

ddi: 3, 5, 5mp, 6, 6mp, 7, 7mp, 7.1, 7.1mp, 8, 8mp

References

SV_ALLOC(D3), SV_BROADCAST(D3), SV_DEALLOC(D3), SV_SIGNAL(D3), SV_WAIT_SIG(D3)

``Synchronization variables'' in HDK Technical Reference