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SubjectRe: Linus on Linux, Apache and Threads
Date
From
> how does the event waiter thread determine whether there is a
> suitable/idle worker thread to awaken?

like this?

struct Q {
struct Q *next;
pthread_t worker;
int fd;
pthread_cond_t sleep;
} *head, *tail;
int Qlen;
pthread_cond_t Qlow;
pthread_mutex_t QLOCK;
void workerthread() {
struct Q *this;
while (1) {
pthread_cond_wait(this->sleep);
/* work on fd here... */
this->next=NULL;
pthread_mutex_lock(QLOCK);
tail->next=this;
tail=this;
++Qlen;
pthread_mutex_unlock(QLOCK);
}
}
void qwatcherthread() {
struct Q *new;
while (1) {
pthread_cond_wait(Qlow);
new=create_new_worker();
new->next=NULL;
pthread_mutex_lock(QLOCK);
tail->next=new;
tail=new;
++Qlen;
pthread_mutex_unlock(QLOCK);
}
}
void acceptor() {
struct Q *work;
while (1) {
if (Qlen<min_workers)
pthread_cond_signal(Qlow);
newfd=accept(...);
pthread_mutex_lock(QLOCK);
if (head) {
--Qlen;
work=head;
head=head->next;
} else {
work=create_new_worker();
}
pthread_mutex_unlock(QLOCK);
work->fd=newfd;
pthtread_cond_signal(work->sleep);
}
}
(no, I don't claim this code is correct, but just to illustrate how it
could be done :-)

Olaf


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