Systemsoftware

Beispiel 3: Verwaltung eines Ressourcen-Pools
MONITOR DiscPool (int Zahl)
enum
{frei,belegt} DiscStatus[N];
int busy; /*Zahl Laufwerke*/
Condition nonbusy;
ENTRY int GetDisc() {
int i;
i=1;
if (busy==N)
nonbusy.Wait();
while (DiscStatus[i]==belegt)
i++;
DiscStatus[i]=belegt;
busy++;
return i;
}
ENTRY PutDisc(int UsedDisc) {
DiscStatus[UsedDisc]=frei;
busy--;
nonbusy.Signal();
}
INIT {
N=...; /*Anzahl Laufwerke*/
DiscStatus[0]=frei;
DiscStatus[1]=frei;
.....
DiscStatus[N-1]=frei;
busy=0;
}
END DiscPool
Systemsoftware - Lektion X 11
Beispiel 4: Reader-Writer-Problem (Reader-Bevorzugung)
MONITOR ReadWrite
int ReadCount, Writeflag;
Condition OKtoRead,OKtoWrite;
ENTRY StartRead() {
Readcount++;
if (Writeflag==1)
OKtoRead.Wait();
OKtoRead.Signal();
}
ENTRY EndRead() {
Readcount--;
if (Readcount==0)
OKtoWrite.Signal();
}
ENTRY StartWrite() {
if ((Readcount>0)¦¦
(Writeflag==1))
OKtoWrite.Wait();
Writeflag=1;
}
ENTRY EndWrite() {
Writeflag=0;
if (OKtoRead.Status()>0)
OKtoRead.Signal();
else OKtoWrite.Signal();
}
INIT {
Readcount=0;
Writeflag=0;
}
END ReadWrite
Systemsoftware - Lektion X 12