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m4/open-max.m4

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+#serial 1
+# Determine approximately how many files may be open simultaneously
+# in one process.  This is approximate, since while running this test,
+# the configure script already has a few files open.
+# From Jim Meyering
+
+AC_DEFUN([UTILS_SYS_OPEN_MAX],
+[
+  AC_CACHE_CHECK([determine how many files may be open simultaneously],
+                 utils_cv_sys_open_max,
+  [
+  AC_RUN_IFELSE([AC_LANG_SOURCE([[
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+    int
+    main ()
+    {
+      FILE *result = fopen ("conftest.omax", "w");
+      int i = 1;
+      /* Impose an arbitrary limit, in case some system has no
+	 effective limit on the number of simultaneously open files.  */
+      while (i < 30000)
+	{
+	  FILE *s = fopen ("conftest.op", "w");
+	  if (!s)
+	    break;
+	  ++i;
+	}
+      fprintf (result, "%d\n", i);
+      exit (fclose (result) == EOF);
+    }
+  ]])],
+       [utils_cv_sys_open_max=`cat conftest.omax`],
+       [utils_cv_sys_open_max='cross compiling run-test in open-max.m4'],
+       [utils_cv_sys_open_max='internal error in open-max.m4'])])
+
+  AC_DEFINE_UNQUOTED([UTILS_OPEN_MAX],
+    $utils_cv_sys_open_max,
+    [the maximum number of simultaneously open files per process])
+])