<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"> <!--Converted with LaTeX2HTML 96.1-c (Feb 29, 1996) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds --> <HTML> <HEAD> <TITLE>Kernel sem structure</TITLE> <META NAME="description" CONTENT="Kernel sem structure"> <META NAME="keywords" CONTENT="lpg"> <META NAME="resource-type" CONTENT="document"> <META NAME="distribution" CONTENT="global"> <LINK REL=STYLESHEET HREF="lpg.css"> </HEAD> <BODY LANG="EN"> <A NAME="tex2html1002" HREF="node51.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="/icons//next_motif.gif"></A> <A NAME="tex2html1000" HREF="node48.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="/icons//up_motif.gif"></A> <A NAME="tex2html996" HREF="node49.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="/icons//previous_motif.gif"></A> <A NAME="tex2html1004" HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="/icons//contents_motif.gif"></A> <BR> <B> Next:</B> <A NAME="tex2html1003" HREF="node51.html">SYSTEM CALL: semget()</A> <B>Up:</B> <A NAME="tex2html1001" HREF="node48.html">Internal Data Structures</A> <B> Previous:</B> <A NAME="tex2html997" HREF="node49.html">Kernel semid_ds structure</A> <BR> <P> <H4><A NAME="SECTION00743220000000000000">Kernel <TT>sem</TT> structure</A></H4> <P> In the <TT>semid_ds</TT> structure, there exists a pointer to the base of the semaphore array itself. Each array member is of the <TT>sem</TT> structure type. It is also defined in <TT>linux/sem.h</TT>: <P> <P> <HR><PRE> /* One semaphore structure for each semaphore in the system. */ struct sem { short sempid; /* pid of last operation */ ushort semval; /* current value */ ushort semncnt; /* num procs awaiting increase in semval */ ushort semzcnt; /* num procs awaiting semval = 0 */ };</PRE> <HR><DL ><DT><STRONG><TT>sem_pid</TT></STRONG> <DD> <P> The PID (process ID) that performed the last operation <P> <DT><STRONG><TT>sem_semval</TT></STRONG> <DD> <P> The current value of the semaphore <P> <DT><STRONG><TT>sem_semncnt</TT></STRONG> <DD> <P> Number of processes waiting for resources to become available <P> <DT><STRONG><TT>sem_semzcnt</TT></STRONG> <DD> <P> Number of processes waiting for 100% resource utilization <P> </DL><BR> <HR> <P><ADDRESS> <I>Converted on: <BR> Fri Mar 29 14:43:04 EST 1996</I> </ADDRESS> </BODY> </HTML>