Original bug ID: 3727
Reporter: administrator
Status: closed
Resolution: fixed
Priority: normal
Severity: minor
Category: ~DO NOT USE (was: OCaml general)

Bug description

Hi,

I found that when I used camlzip's "minizip" to unpack an archive, it
was muuuch slower than "unzip". It turned out that this was due to
a linear search in unlinking channels from the global list.

By adding a "prev" pointer, I got the speed of minizip down to the speed
of "unzip".

--chet--

--- io.c.1 2004-01-08 17:28:48.000000000 -0500
+++ io.c 2005-07-15 13:40:29.000000000 -0400
@@ -15,6 +15,7 @@

/* Buffered input/output. */

+#include <stdio.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
@@ -70,6 +71,9 @@
channel->old_revealed = 0;
channel->refcount = 0;
channel->next = caml_all_opened_channels;

• channel->prev = NULL;
• if (NULL != caml_all_opened_channels)
• caml_all_opened_channels->prev = channel;
  caml_all_opened_channels = channel;
  return channel;
  }
  @@ -84,14 +88,30 @@
  }

static void unlink_channel(struct channel *channel)
+#if 1
+{

• Assert (caml_all_opened_channels);

• if (NULL == channel->prev) {

• Assert (channel == caml_all_opened_channels);

• caml_all_opened_channels = caml_all_opened_channels->next;

• if (caml_all_opened_channels) caml_all_opened_channels->prev = NULL;

• } else {

• channel->prev->next = channel->next;

• if (channel->next) channel->next->prev = channel->prev;

• }
  +}
  +#else
  {
  struct channel ** cp = &caml_all_opened_channels;

  while (*cp != channel && *cp != NULL)
  cp = &(*cp)->next;

• if (*cp != NULL)

• if (*cp != NULL) {
  *cp = (*cp)->next;
  }
  +}
  +#endif

CAMLexport void caml_close_channel(struct channel channel)
{
--- io.h.1 2004-01-01 11:42:36.000000000 -0500
+++ io.h 2005-07-15 13:24:35.000000000 -0400
@@ -40,6 +40,7 @@
char * max; / Logical end of the buffer (for input) /
void * mutex; / Placeholder for mutex (for systhreads) /
struct channel * next; / Linear chaining of channels (flush_all) */

• struct channel * prev; /* Linear chaining of channels (flush_all) /
  int revealed; / For Cash only /
  int old_revealed; / For Cash only /
  int refcount; / For flush_all and for Cash */