Fix for 'Too many open files' errors

[Zack Weinberg]

This patch makes cpp detect an EMFILE or ENFILE error return from
open() and close all its cached file descriptors.  This should make it
possible to bootstrap again on systems with a small limit on open
files per process.  (We can look into cleverer cache-replacement
policies later; the important bit right now is to get things working.)

The patch also adds the ability to report on headers that could use
multiple include guards.  Right now this is triggered by -H; I'm open
to user-interface suggestions.  At the end of preprocessing you get a
list of all the headers that were read only once but that don't have
multiple include guards.  You can't blindly add guards to all files so
listed, but it gives you a place to start.

Bootstrapped and tested on i386-linux.  I'll hold off committing it
until I hear a success report for one of the affected systems.

[For those unclear on the difference: EMFILE is for the per-process
limit on open files, ENFILE is the system-wide limit.]

zw

	* cppfiles.c (open_include_file): If open(2) returns EMFILE or 
	ENFILE,	close all cached file descriptors and try again.
	(_cpp_execute_include): Keep a count of the number of times
	each header is included.
	(close_cached_fd): New function.
	* cpphash.h (struct include_file): Rename before to
	include_count; all users updated.  Make include_count and sysp
	unsigned short.
	* cppinit.c (cpp_finish): If -H, report headers that could use 
	reinclude guards.
	(report_missing_guard): New function.

===================================================================
Index: cppfiles.c
--- cppfiles.c	2000/06/21 23:08:17	1.67
+++ cppfiles.c	2000/06/28 07:08:41
@@ -60,6 +60,7 @@ static ssize_t read_with_read	PARAMS ((c
 static ssize_t read_file	PARAMS ((cpp_buffer *, int, ssize_t));
 
 static void destroy_include_file_node	PARAMS ((splay_tree_value));
+static int close_cached_fd	PARAMS ((splay_tree_node, void *));
 
 #if 0
 static void hack_vms_include_specification PARAMS ((char *));
@@ -87,6 +88,20 @@ destroy_include_file_node (v)
     }
 }
 
+static int
+close_cached_fd (n, dummy)
+     splay_tree_node n;
+     void *dummy ATTRIBUTE_UNUSED;
+{
+  struct include_file *f = (struct include_file *)n->value;
+  if (f && f->fd != -1)
+    {
+      close (f->fd);
+      f->fd = -1;
+    }
+  return 0;
+}
+
 void
 _cpp_init_include_table (pfile)
      cpp_reader *pfile;
@@ -153,6 +168,8 @@ open_include_file (pfile, filename)
      ourselves.
 
      Special case: the empty string is translated to stdin.  */
+ retry:
+
   if (filename[0] == '\0')
     fd = 0;
   else
@@ -167,6 +184,21 @@ open_include_file (pfile, filename)
 		     filename);
 	}
 #endif
+      if (0
+#ifdef EMFILE
+	  || errno == EMFILE
+#endif
+#ifdef ENFILE
+	  || errno == ENFILE
+#endif
+	  )
+	{
+	  /* Too many files open.  Close all cached file descriptors and
+	     try again.  */
+	  splay_tree_foreach (pfile->all_include_files, close_cached_fd, 0);
+	  goto retry;
+	}
+
       /* Nonexistent or inaccessible file.  Create a negative node for it.  */
       if (nd)
 	{
@@ -185,7 +217,7 @@ open_include_file (pfile, filename)
     {
       file = xnew (struct include_file);
       file->cmacro = 0;
-      file->before = 0;
+      file->include_count = 0;
       file->sysp = 0;
       file->foundhere = 0;
       file->name = xstrdup (filename);
@@ -367,9 +399,9 @@ _cpp_execute_include (pfile, f, len, no_
 	return;
 
       /* For -M, add the file to the dependencies on its first inclusion. */
-      if (!inc->before && PRINT_THIS_DEP (pfile, angle_brackets))
+      if (!inc->include_count && PRINT_THIS_DEP (pfile, angle_brackets))
 	deps_add_dep (pfile->deps, inc->name);
-      inc->before = 1;
+      inc->include_count++;
 
       /* Handle -H option.  */
       if (CPP_OPTION (pfile, print_include_names))
===================================================================
Index: cpphash.h
--- cpphash.h	2000/06/21 18:33:51	1.54
+++ cpphash.h	2000/06/28 07:08:41
@@ -62,8 +62,8 @@ struct include_file
 				/* location in search path where file was
 				   found, for #include_next */
   int fd;			/* file descriptor possibly open on file */
-  unsigned char before;		/* file has been included before */
-  unsigned char sysp;		/* file is a system header */
+  unsigned short include_count;	/* number of times file has been read */
+  unsigned short sysp;		/* file is a system header */
 };
 
 /* The cmacro works like this: If it's NULL, the file is to be
===================================================================
Index: cppinit.c
--- cppinit.c	2000/06/21 18:33:51	1.83
+++ cppinit.c	2000/06/28 07:08:42
@@ -227,6 +227,7 @@ static int opt_comp			PARAMS ((const voi
 #endif
 static int parse_option			PARAMS ((const char *));
 static int handle_option		PARAMS ((cpp_reader *, int, char **));
+static int report_missing_guard		PARAMS ((splay_tree_node, void *));
 
 /* Fourth argument to append_include_chain: chain to use */
 enum { QUOTE = 0, BRACKET, SYSTEM, AFTER };
@@ -1003,6 +1004,27 @@ cpp_start_read (pfile, print, fname)
   return 1;
 }
 
+static int
+report_missing_guard (n, b)
+     splay_tree_node n;
+     void *b;
+{
+  struct include_file *f = (struct include_file *) n->value;
+  int *bannerp = (int *)b;
+
+  if (f && f->cmacro == 0 && f->include_count == 1)
+    {
+      if (*bannerp == 0)
+	{
+	  fputs (_("Multiple include guards may be useful for:\n"), stderr);
+	  *bannerp = 1;
+	}
+      fputs (f->name, stderr);
+      putc ('\n', stderr);
+    }
+  return 0;
+}
+
 /* This is called at the end of preprocessing.  It pops the
    last buffer and writes dependency output.  It should also
    clear macro definitions, such that you could call cpp_start_read
@@ -1054,6 +1076,14 @@ cpp_finish (pfile, print)
       cpp_output_tokens (pfile, print);
       if (ferror (print->outf) || fclose (print->outf))
 	cpp_notice_from_errno (pfile, CPP_OPTION (pfile, out_fname));
+    }
+
+  /* Report on headers that could use multiple include guards.  */
+  if (CPP_OPTION (pfile, print_include_names))
+    {
+      int banner = 0;
+      splay_tree_foreach (pfile->all_include_files, report_missing_guard,
+			  (void *) &banner);
     }
 }