SVR5

wakeup(D3)

wakeup -- resume suspended process execution

Synopsis (Not in current DDI version)

   #include <sys/types.h>
   #include <sys/ddi.h>
   
   void wakeup(caddr_t event);

Description

wakeup awakens all processes sleeping on the address specified by event and makes them eligible for scheduling.

Arguments

event: Address that was passed to the corresponding call to sleep(D3) which caused the process to be suspended.

Return values

None

Usage

The same event argument must be used for corresponding calls to sleep and wakeup. It is recommended for code readability and for efficiency to have a one-to-one correspondence between events and sleep addresses.

Whenever a driver returns from a call to sleep, it should test to ensure that the event for which the driver slept actually occurred. There is an interval between the time the process that called sleep is awakened and the time it resumes execution where the state forcing the sleep may have been reentered. This can occur because all processes waiting for an event are awakened at the same time. The first process selected for execution by the scheduler usually gains control of the event. All other processes awakened should recognize that they cannot continue and should reissue the sleep call.

Context and synchronization

Non-blockable, interrupt, user, or blockable context.

Hardware applicability

All

Version applicability

ddi: 1, 2, 3, 4, 5, 5mp, 6, 6mp

Differences between versions

Starting with DDI version 7, SV_BROADCAST(D3) and SV_SIGNAL(D3) replace wakeup( ). These new functions are much faster, since they avoid the hash table insertion and lookup that are needed to unblock the process based on an arbitrary channel number. Instead, they are passed a driver-owned sv-t object which directly tracks sleeping LWPs. See ``Synchronization variables'' in HDK Technical Reference.

Under some conditions, even greater performance can be achieved by using SV_SIGNAL( ), which only wakes up one LWP, rather than waking up all the sleeping LWPs and then having all but one go back to sleep again. SV_SIGNAL( ) must, however, be used with care.

References

sleep(D3)

``Synchronization variables'' in HDK Technical Reference