uexblock Kernel Service

Purpose

Makes the currently active kernel thread nonrunnable when called from a user-mode exception handler.

Syntax

#include <sys/types.h>
#include <sys/errno.h>
#include <sys/except.h>

Parameter

Description

The uexblock kernel service puts the currently active kernel thread that is specified by the tid parameter into a wait state until the uexclear kernel service is used to make the thread runnable again. If the uexblock kernel service is called from the process environment, the tid parameter must specify the current active thread; otherwise the system crashes with a kernel panic.

The uexblock kernel service can be used to lazily control user-mode threads access to a shared serially usable resource. Multiple threads can use a serially used resource, but only one process at a time. When a thread attempts to but cannot access the resource, a user-mode exception can be set up to occur. This gives control to an exception handler registered by the uexadd kernel service. This exception handler can then block the thread by using the uexblock kernel service until the resource is made available. At this time, the uexclear kernel service can be used to make the blocked thread runnable.

Execution Environment

The uexblock kernel service can be called from either the process or interrupt environment.

Return Values

The uexblock service has no return values.