[commit: ghc] master: fdReady: use poll() instead of select() (f46369b)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/f46369b8a1bf90a3bdc30f2b566c3a7e03672518/ghc

>---------------------------------------------------------------

commit f46369b8a1bf90a3bdc30f2b566c3a7e03672518
Author: Simon Marlow <marlowsd at gmail.com>
Date:   Fri Dec 2 14:32:24 2016 -0500

    fdReady: use poll() instead of select()
    
    select() is limited to 1024 file descriptors.  This actually blew up
    in a very hard-to-debug way in our production system when using the
    hinotify package.
    
    Test Plan:
    libraries/tests pass, paricularly hGetBuf001 which exercises this
    code.
    
    Reviewers: niteria, erikd, austin, hvr, bgamari
    
    Reviewed By: bgamari
    
    Subscribers: thomie
    
    Differential Revision: https://phabricator.haskell.org/D2785
    
    GHC Trac Issues: #12912


>---------------------------------------------------------------

f46369b8a1bf90a3bdc30f2b566c3a7e03672518
 libraries/base/cbits/inputReady.c | 42 ++++++++++++++++++++++++++++++---------
 1 file changed, 33 insertions(+), 9 deletions(-)

diff --git a/libraries/base/cbits/inputReady.c b/libraries/base/cbits/inputReady.c
index 8714eea..230e592 100644
--- a/libraries/base/cbits/inputReady.c
+++ b/libraries/base/cbits/inputReady.c
@@ -7,6 +7,9 @@
 /* select and supporting types is not Posix */
 /* #include "PosixSource.h" */
 #include "HsBase.h"
+#if !defined(_WIN32)
+#include <poll.h>
+#endif
 
 /*
  * inputReady(fd) checks to see whether input is available on the file
@@ -16,19 +19,41 @@
 int
 fdReady(int fd, int write, int msecs, int isSock)
 {
-    if 
-#if defined(_WIN32)
-    ( isSock ) {
+
+#if !defined(_WIN32)
+
+    // We only handle msecs == 0 on non-Windows, because this is the
+    // only case we need.  Non-zero waiting is handled by the IO manager.
+    if (msecs != 0) {
+        fprintf(stderr, "fdReady: msecs != 0, this shouldn't happen");
+        abort();
+    }
+
+    struct pollfd fds[1];
+
+    fds[0].fd = fd;
+    fds[0].events = write ? POLLOUT : POLLIN;
+    fds[0].revents = 0;
+
+    int res;
+    while ((res = poll(fds, 1, 0)) < 0) {
+        if (errno != EINTR) {
+            return (-1);
+        }
+    }
+
+    // res is the number of FDs with events
+    return (res > 0);
+
 #else
-    ( 1 ) {
-#endif
+
+    if (isSock) {
 	int maxfd, ready;
 	fd_set rfd, wfd;
 	struct timeval tv;
         if ((fd >= (int)FD_SETSIZE) || (fd < 0)) {
-            /* avoid memory corruption on too large FDs */
-            errno = EINVAL;
-            return -1;
+            fprintf(stderr, "fdReady: fd is too big");
+            abort();
         }
 	FD_ZERO(&rfd);
 	FD_ZERO(&wfd);
@@ -54,7 +79,6 @@ fdReady(int fd, int write, int msecs, int isSock)
 	/* 1 => Input ready, 0 => not ready, -1 => error */
 	return (ready);
     }
-#if defined(_WIN32)
     else {
 	DWORD rc;
 	HANDLE hFile = (HANDLE)_get_osfhandle(fd);