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Date: Mon, 25 Oct 2010 19:26:33 +0200
From: =?iso-8859-1?Q?J=E9r=E9mie?= Dimino <jeremie@dimino.org>
To: Yaron Minsky <yminsky@gmail.com>
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] Asynchronous IO programming in OCaml
Message-ID: <20101025172633.GC32282@aurora>
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X-Spam: no; 0.00; ocaml:01 yaron:01 minsky:01 fcntl:01 unistd:01 buffer:01 4096:01 buffer:01 4096:01 fcntl:01 unistd:01 char:01 char:01 wrote:01 caml-list:01 

On Mon, Oct 25, 2010 at 11:34:41AM -0400, Yaron Minsky wrote:
>    I don't quite understand how this whole benchmark holds together.  Could
>    you post the C code?  I don't understand the differences between (1), (2)
>    and (3) well enough to explain where the factor of 100 comes in.

Yes. Here is the code of the first program:

,----
| #include <sys/types.h>
| #include <sys/stat.h>
| #include <fcntl.h>
| #include <unistd.h>
| 
| int main()
| {
|   int fd = open("data", O_RDONLY);
|   char buffer[4096];
| 
|   while (read(fd, buffer, 4096) > 0);
| 
|   close(fd);
| 
|   return 0;
| }
`----

the code of the second:

,----
| #include <sys/types.h>
| #include <sys/stat.h>
| #include <fcntl.h>
| #include <unistd.h>
| #include <pthread.h>
| 
| int fd;
| char buffer[4096];
| int done = 0;
| 
| void *callback(void* data)
| {
|   int count = read(fd, buffer, 4096);
|   if (count == 0) done = 1;
|   return NULL;
| }
| 
| int main()
| {
|   fd = open("data", O_RDONLY);
| 
|   while (!done) {
|     pthread_t thread;
|     pthread_create(&thread, NULL, callback, NULL);
|     pthread_join(thread, NULL);
|   }
| 
|   close(fd);
| 
|   return 0;
| }
`----

and the third:

,----
| #include <sys/types.h>
| #include <sys/stat.h>
| #include <fcntl.h>
| #include <unistd.h>
| #include <pthread.h>
| 
| int fd;
| char buffer[4096];
| int done = 0;
| pthread_cond_t start = PTHREAD_COND_INITIALIZER;
| pthread_cond_t stop = PTHREAD_COND_INITIALIZER;
| pthread_mutex_t start_mutex = PTHREAD_MUTEX_INITIALIZER;
| pthread_mutex_t stop_mutex = PTHREAD_MUTEX_INITIALIZER;
| 
| void *callback(void* data)
| {
|   while (!done) {
|     pthread_cond_wait(&start, &start_mutex);
| 
|     int count = read(fd, buffer, 4096);
|     if (count == 0) done = 1;
| 
|     pthread_mutex_lock(&stop_mutex);
|     pthread_cond_signal(&stop);
|     pthread_mutex_unlock(&stop_mutex);
|   }
|   return NULL;
| }
| 
| int main()
| {
|   fd = open("data", O_RDONLY);
| 
|   pthread_cond_init(&start, NULL);
|   pthread_cond_init(&stop, NULL);
| 
|   pthread_mutex_lock(&start_mutex);
|   pthread_mutex_lock(&stop_mutex);
| 
|   pthread_t thread;
|   pthread_create(&thread, NULL, callback, NULL);
| 
|   while (!done) {
|     pthread_mutex_lock(&start_mutex);
|     pthread_cond_signal(&start);
|     pthread_mutex_unlock(&start_mutex);
| 
|     pthread_cond_wait(&stop, &stop_mutex);
|   }
| 
|   pthread_join(thread, NULL);
|   close(fd);
| 
|   return 0;
| }
`----

Jérémie