Add `scm_std_read ()'

[Ludovic Courtès]

Hi,

This is roughly a followup to:

  http://thread.gmane.org/gmane.lisp.guile.devel/6549/focus=6613

The attached patch adds an `scm_std_read ()' call, which is to read(2)
what `scm_std_select ()' is to select(2).  It changes `fport_fill_input'
to use it, which removes the call to select(2) that precedes each
read(2) call (!).

Using the same "I/O benchmark" as in my previous message, and compared
to Guile with the inlined `scm_getc' patch, it yields an additional 5%
speedup when reading by 4096-octet blocks, and a negligible improvement
when using smaller buffer sizes.

OK to apply?

Thanks,
Ludovic.

>From f305530cbd31b4a0963f40ed9a7dd27a94aa05a8 Mon Sep 17 00:00:00 2001
From: =?utf-8?q?Ludovic=20Court=C3=A8s?= <address@hidden>
Date: Mon, 14 Apr 2008 22:52:37 +0200
Subject: [PATCH] Add `scm_std_read ()', use it in `fport_fill_input ()'.

---
 libguile/fports.c  |   32 +-------------------------------
 libguile/threads.c |   24 +++++++++++++++++++++++-
 libguile/threads.h |    2 ++
 3 files changed, 26 insertions(+), 32 deletions(-)

diff --git a/libguile/fports.c b/libguile/fports.c
index efbd278..7817808 100644
--- a/libguile/fports.c
+++ b/libguile/fports.c
@@ -553,33 +553,6 @@ fport_print (SCM exp, SCM port, scm_print_state *pstate 
SCM_UNUSED)
   return 1;
 }
 
-#ifndef __MINGW32__
-/* thread-local block for input on fport's fdes.  */
-static void
-fport_wait_for_input (SCM port)
-{
-  int fdes = SCM_FSTREAM (port)->fdes;
-
-  if (!fport_input_waiting (port))
-    {
-      int n;
-      SELECT_TYPE readfds;
-      int flags = fcntl (fdes, F_GETFL);
-
-      if (flags == -1)
-       scm_syserror ("scm_fdes_wait_for_input");
-      if (!(flags & O_NONBLOCK))
-       do
-         {
-           FD_ZERO (&readfds);
-           FD_SET (fdes, &readfds);
-           n = scm_std_select (fdes + 1, &readfds, NULL, NULL, NULL);
-         }
-       while (n == -1 && errno == EINTR);
-    }
-}
-#endif /* !__MINGW32__ */
-
 static void fport_flush (SCM port);
 
 /* fill a port's read-buffer with a single read.  returns the first
@@ -591,10 +564,7 @@ fport_fill_input (SCM port)
   scm_t_port *pt = SCM_PTAB_ENTRY (port);
   scm_t_fport *fp = SCM_FSTREAM (port);
 
-#ifndef __MINGW32__
-  fport_wait_for_input (port);
-#endif /* !__MINGW32__ */
-  SCM_SYSCALL (count = read (fp->fdes, pt->read_buf, pt->read_buf_size));
+  count = scm_std_read (fp->fdes, pt->read_buf, pt->read_buf_size);
   if (count == -1)
     scm_syserror ("fport_fill_input");
   if (count == 0)
diff --git a/libguile/threads.c b/libguile/threads.c
index 68c5f79..84aa5ea 100644
--- a/libguile/threads.c
+++ b/libguile/threads.c
@@ -1690,7 +1690,8 @@ scm_threads_mark_stacks (void)
   SCM_MARK_BACKING_STORE ();
 }
 
-/*** Select */
+
+/* Convenience API for I/O that properly leaves guile mode when blocking.  */
 
 int
 scm_std_select (int nfds,
@@ -1741,6 +1742,27 @@ scm_std_select (int nfds,
   return res;
 }
 
+ssize_t
+scm_std_read (int fd, void *buf, size_t size)
+{
+  int eno;
+  ssize_t count;
+  scm_t_guile_ticket ticket;
+
+  SCM_TICK;
+
+  ticket = scm_leave_guile ();
+
+  SCM_SYSCALL (count = read (fd, buf, size));
+  eno = errno;
+
+  scm_enter_guile (ticket);
+
+  errno = eno;
+  return count;
+}
+
+
 /* Convenience API for blocking while in guile mode. */
 
 #if SCM_USE_PTHREAD_THREADS
diff --git a/libguile/threads.h b/libguile/threads.h
index e1944a5..aac6b0b 100644
--- a/libguile/threads.h
+++ b/libguile/threads.h
@@ -224,6 +224,8 @@ SCM_API int scm_pthread_cond_timedwait (pthread_cond_t 
*cond,
 
 SCM_API unsigned int scm_std_sleep (unsigned int);
 SCM_API unsigned long scm_std_usleep (unsigned long);
+SCM_API ssize_t scm_std_read (int, void *, size_t);
+
 
 #endif  /* SCM_THREADS_H */
 
-- 
1.5.5

>From 823a559a47866bd6dbbe93161938581b32b050a0 Mon Sep 17 00:00:00 2001
From: =?utf-8?q?Ludovic=20Court=C3=A8s?= <address@hidden>
Date: Tue, 15 Apr 2008 09:34:29 +0200
Subject: [PATCH] Document `scm_std_read ()'.

---
 doc/ref/api-scheduling.texi |   11 +++++++----
 1 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/doc/ref/api-scheduling.texi b/doc/ref/api-scheduling.texi
index ec136fb..9916e7e 100644
--- a/doc/ref/api-scheduling.texi
+++ b/doc/ref/api-scheduling.texi
@@ -1,6 +1,6 @@
 @c -*-texinfo-*-
 @c This is part of the GNU Guile Reference Manual.
address@hidden Copyright (C)  1996, 1997, 2000, 2001, 2002, 2003, 2004, 2007
address@hidden Copyright (C)  1996, 1997, 2000, 2001, 2002, 2003, 2004, 2007, 
2008
 @c   Free Software Foundation, Inc.
 @c See the file guile.texi for copying conditions.
 
@@ -583,9 +583,12 @@ leaves guile mode while waiting for the condition variable.
 @end deftypefn
 
 @deftypefn {C Function} int scm_std_select (int nfds, fd_set *readfds, fd_set 
*writefds, fd_set *exceptfds, struct timeval *timeout)
-Like @code{select} but leaves guile mode while waiting.  Also, the
-delivery of a system async causes this function to be interrupted with
-error code @code{EINTR}.
address@hidden {C Function} ssize_t scm_std_read (int fd, void *buffer, size_t 
size)
+Like the C library @code{select} and @code{read} (@pxref{Low-Level I/O,
+Low-Level Input/Output,, libc, The GNU C Library Reference Manual}),
+respectively, but leaves guile mode while waiting.  Also, the delivery
+of a system async causes this function to be interrupted with error code
address@hidden
 @end deftypefn
 
 @deftypefn {C Function} {unsigned int} scm_std_sleep ({unsigned int} seconds)
-- 
1.5.5