[screen-devel] [PATCH for screen-v4] Make closeallfiles() faster

[Amadeusz Sławiński]

Optimize startup time, making closeallfiles() faster, by doing less
system calls. Instead of calling close for each possible file, use
poll() to check if file exist at all. On linux with open file limit set
to 1048576, it should do 1024 poll() calls instead of 1048576 close().

Bug: 55618

Signed-off-by: Amadeusz Sławiński <address@hidden>
---
 src/misc.c | 33 ++++++++++++++++++++++++++++++---
 1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/src/misc.c b/src/misc.c
index 43e93a2a..52f8514e 100644
--- a/src/misc.c
+++ b/src/misc.c
@@ -26,6 +26,7 @@
  ****************************************************************
  */
 
+#include <poll.h>
 #include <sys/types.h>
 #include <sys/stat.h>  /* mkdir() declaration */
 #include <signal.h>
@@ -379,12 +380,38 @@ int except;
 #endif /* SVR4 */
 #if defined(SYSV) && defined(NOFILE) && !defined(ISC)
   f = NOFILE;
-#else /* SYSV && !ISC */
-  f = getdtablesize();
-#endif /* SYSV && !ISC */
   while (--f > 2)
     if (f != except)
       close(f);
+#else /* SYSV && !ISC */
+  {
+    struct pollfd pfd[1024];
+    int maxfd, i, ret, z;
+
+    i = 3; /* skip stdin, stdout and stderr */
+    maxfd = getdtablesize();
+
+    while (i < maxfd)
+      {
+        memset(pfd, 0, sizeof(pfd));
+
+        z = 0;
+        for (f = i; f < maxfd && f < i + 1024; f++)
+          pfd[z++].fd = f;
+
+        ret = poll(pfd, f - i, 0);
+        if (ret < 0)
+          Panic(errno, "poll");
+
+        z = 0;
+        for (f = i; f < maxfd && f < i + 1024; f++)
+          if (!(pfd[z++].revents & POLLNVAL) && f != except)
+            close(f);
+
+        i = f;
+      }
+  }
+#endif /* SYSV && !ISC */
 }
 
 #endif /* HAVE_FDWALK */
-- 
2.23.0