Concurrency en race condities

monitor ReadersAndWriters {
static int Readers = 0;
static int SomeoneIsWriting = 0;
static condition ReadingAllowed,
WritingAllowed;
startRead () {
if (SomeoneIsWriting ||
Readers++;
Readers/writers monitor
queue(WritingAllowed))
wait(ReadingAllowed);
signal(ReadingAllowed);
}
endRead () {
Readers--;
if (Readers == 0)
signal(WritingAllowed);
}
}
startWrite () {
}
if ((Readers > 0) ||
endWrite () {
}
SomeoneIsWriting)
wait(WritingAllowed);
SomeoneIsWriting = 1;
SomeoneIsWriting = 0;
if (queue(ReadingAllowed))
signal(ReadingAllowed);
else
signal(WritingAllowed);
College OS 2010 – 2011 44