Roy's musings

I was trying to install the FreeBSD 7.0 in my VMWare virtual machine (VM). After I downloaded the installer disk's ISO image, I connected that ISO file as my CDROM drive in my VM and booted my VM. I should mention that my VM is in NAT mode, as I had decided to install the FreeBSD over the network. When the installation tries to download the distro files from the FTP servers, it just kept saying it could not connect to the FTP server. I wasted around an hour or so without thinking about the basics (Damn!) that I am behind a NAT and I am trying to download files using active FTP mode. Then I tried to connect in passive mode and everything worked fine. I don't want to repeat what many people have already clearly explained about passive mode of FTP. Here is an excellent tutorial that talks about active and passive modes of FTP. Moral of the story is, don't forget that active FTP doesn't work (generally :-) if you are behind a NAT. I would like to add only one thing: I thin...

Simiar to kqueue framework in FreeBSD, Solaris 10 introduced a framework called Event Completion Framework (ECF). ECF is a very powerful concept that can be used when an application wants to wait for asynchronous events - like read/write events on sockets. Traditionally one would use poll()/select() for these events. There is enough discussion already on how primitive these mechanisms are and how they don't scale well on large number of file descriptors. Another advantage with kqueue and ECF is that you can wait on different kind of activities, not just activities on file descriptors. For e.g. when a process calls fork, or when a process calls exit, etc. There are a few resources that would be very useful in understanding these frameworks: Robert Benson's article on ECF Sample program given in Bart Smaalder's blog Jonathan Lemon's paper on kqueue Oh btw, I think Linux is yet to have a mechanism as powerful as these.

Let us begin with the sample code below (headers omitted for brevity): int main(int argc, const char* argv[]) { void* mmap_ptr = mmap (NULL, sizeof (pthread_mutex_t), PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANON, -1, 0); if (mmap_ptr == MAP_FAILED) { perror ("mmap failed"); return -1; } fprintf (stderr, "mmaped at: %x\n", mmap_ptr); pthread_mutex_t* mutp = (pthread_mutex_t*)mmap_ptr; // initialize the attribute pthread_mutexattr_t attr; pthread_mutexattr_init (&attr); pthread_mutexattr_setpshared (&attr, PTHREAD_PROCESS_SHARED); // this is what we're testing // initialize the mutex pthread_mutex_init (mutp, &attr); pthread_mutexattr_destroy (&attr); // acquire the lock before fork pthread_mutex_lock (mutp); pid_t chld = fork (); if (chld != 0) { // parent fprintf (stderr, "parent: going to sleep...\n"); sleep (30); fprintf (stderr, "parent: unlocking.\n"); pthread_mutex_unlock (mutp); } else { /...