0005416: Unix.(set|clear)_close_on_exec changes sockets to blocking mode

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Date Submitted

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0005416

OCaml

OCaml general

public

2011-12-08 14:11

2012-02-27 18:14

Reporter

ripoche

Assigned To

Priority

normal

Severity

major

Reproducibility

always

Status

resolved

Resolution

fixed

Platform

Windows

OS Version

XP SP3 32 bits

Product Version

3.12.1

Target Version

Fixed in Version

Summary

0005416: Unix.(set|clear)_close_on_exec changes sockets to blocking mode

Description

Consider the following snippet:

let () =
  let server = Unix.socket Unix.PF_INET Unix.SOCK_STREAM 0 in
    Unix.set_nonblock server;
    Unix.set_close_on_exec server;
    Unix.setsockopt server Unix.SO_REUSEADDR true;
    Unix.bind server (Unix.ADDR_INET (Unix.inet_addr_any, 1039));
    Unix.listen server 10;
      output_string stdout "calling Unix.accept on non-blocking socket\n";
      flush stdout;
      ignore (Unix.accept server)
;;

On Linux 32 bits, the call to accept fails as expected with EAGAIN (EWOULDBLOCK would be fine too).
On WinXP SP3 32 bits, the call to accept blocks.

This issue lies in the Win32 implementation of Unix.(set|clear)_close_on_exec. otherlibs/win32unix/close_on.c uses DuplicateHandle which has the (undocumented) side-effect of resetting sockets to blocking mode.

Note that this trick is from the Win9x era and should probably be replaced by a call to SetHandleInformation.

As a side note, I also noticed the usage of both WinSock and WinSock2 in win32unix. Can I ask what's the point of mixing both ? Do we really need to support Win9X ?

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No tags attached.

Attached Files

ocaml-3.12.1.close_on.patch [^] (935 bytes) 2011-12-08 14:43 [Show Content] [Hide Content]

diff -Naur ocaml-3.12.1.orig/otherlibs/win32unix/close_on.c ocaml-3.12.1/otherlibs/win32unix/close_on.c
--- ocaml-3.12.1.orig/otherlibs/win32unix/close_on.c	2001-12-07 13:41:02.000000000 +0000
+++ ocaml-3.12.1/otherlibs/win32unix/close_on.c	2011-12-08 13:22:34.000000000 +0000
@@ -19,17 +19,14 @@
 
 int win_set_inherit(value fd, BOOL inherit)
 {
-  HANDLE oldh, newh;
-
-  oldh = Handle_val(fd);
-  if (! DuplicateHandle(GetCurrentProcess(), oldh,
-                        GetCurrentProcess(), &newh,
-                        0L, inherit, DUPLICATE_SAME_ACCESS)) {
+  /* According to the MSDN, SetHandleInformation may not work
+     for console handles on WinNT4 and earlier versions. */
+  if (! SetHandleInformation(Handle_val(fd),
+			     HANDLE_FLAG_INHERIT,
+			     inherit ? HANDLE_FLAG_INHERIT : 0)) {
     win32_maperr(GetLastError());
     return -1;
   }
-  Handle_val(fd) = newh;
-  CloseHandle(oldh);
   return 0;
 }

Relationships

related to

0004895

resolved

Windows (mingw): Unix.set/clear_close_on_exec modifies the descriptor

Notes
(0006399) xleroy (administrator) 2011-12-20 10:01	Patch applied in SVN trunk, commit 11888. Re: "what's the point of mixing WinSock and WinSock2?", it's probably historical baggage. I don't know what it would imply to switch entirely to WinSock2 (how many changes? what benefits?). If you have suggestions on this topic, feel free to open another PR with them.

Issue History
Date Modified	Username	Field	Change
2011-12-08 14:11	ripoche	New Issue
2011-12-08 14:43	ripoche	File Added: ocaml-3.12.1.close_on.patch
2011-12-20 10:01	xleroy	Note Added: 0006399
2011-12-20 10:01	xleroy	Status	new => resolved
2011-12-20 10:01	xleroy	Resolution	open => fixed
2012-02-27 18:14	xleroy	Relationship added	related to 0004895