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add cgi_overload_delay tunable
authorJoey Hess <joey@kitenet.net>
Tue, 9 Oct 2012 21:03:52 +0000 (17:03 -0400)
committerJoey Hess <joey@kitenet.net>
Tue, 9 Oct 2012 21:12:04 +0000 (17:12 -0400)
Try to avoid a situation in which so many ikiwiki cgi wrapper programs are
running, all waiting on some long-running thing like a site rebuild, that
it prevents the web server from doing anything else. The current approach
only avoids this problem for GET requests; if multiple cgi's run GETs on a
site at the same time, one will display a "please wait" page for a
configurable number of seconds, which then redirects to retry. To enable
this protection, set cgi_overload_delay to the number of seconds to wait.
This is not enabled by default.

IkiWiki.pm patch | blob | history
IkiWiki/Wrapper.pm patch | blob | history
debian/changelog patch | blob | history

diff --git a/IkiWiki.pm b/IkiWiki.pm
index f68797ae3b962bc7556308fffa0da5d644c46ca3..a7dc6b36bb4557be43cde21d9158f7dd607d5d68 100644 (file)
--- a/IkiWiki.pm
+++ b/IkiWiki.pm
@@ -118,6 +118,14 @@ sub getsetup () {
                safe => 0,
                rebuild => 0,
        },
                safe => 0,
                rebuild => 0,
        },
+       cgi_overload_delay => {
+               type => "string",
+               default => '',
+               example => "10",
+               description => "number of seconds to delay CGI requests when overloaded",
+               safe => 1,
+               rebuild => 0,
+       },
        rcs => {
                type => "string",
                default => '',
        rcs => {
                type => "string",
                default => '',
diff --git a/IkiWiki/Wrapper.pm b/IkiWiki/Wrapper.pm
index 769540d29ac3de34715436ead21416747d3b09b4..0855a3ba2ede3194d0d71a9697db246c1b619c31 100644 (file)
--- a/IkiWiki/Wrapper.pm
+++ b/IkiWiki/Wrapper.pm
@@ -93,12 +93,43 @@ EOF
                # memory, a pile up of processes could cause thrashing
                # otherwise. The fd of the lock is stored in
                # IKIWIKI_CGILOCK_FD so unlockwiki can close it.
                # memory, a pile up of processes could cause thrashing
                # otherwise. The fd of the lock is stored in
                # IKIWIKI_CGILOCK_FD so unlockwiki can close it.
-               $pre_exec=<<"EOF";
+               #
+               # A lot of cgi wrapper processes can potentially build
+               # up and clog an otherwise unloaded web server. To
+               # partially avoid this, when a GET comes in and the lock
+               # is already held, rather than blocking a html page is
+               # constructed that retries. This is enabled by setting
+               # cgi_overload_delay.
+               if (defined $config{cgi_overload_delay} &&
+                   $config{cgi_overload_delay} =~/^[0-9]+/) {
+                       my $i=int($config{cgi_overload_delay});
+                       $pre_exec.="#define CGI_OVERLOAD_DELAY $i\n"
+                               if $i > 0;
+               }
+               $pre_exec.=<<"EOF";
        lockfd=open("$config{wikistatedir}/cgilock", O_CREAT | O_RDWR, 0666);
        lockfd=open("$config{wikistatedir}/cgilock", O_CREAT | O_RDWR, 0666);
-       if (lockfd != -1 && lockf(lockfd, F_LOCK, 0) == 0) {
-               char *fd_s=malloc(8);
-               sprintf(fd_s, "%i", lockfd);
-               setenv("IKIWIKI_CGILOCK_FD", fd_s, 1);
+       if (lockfd != -1) {
+#ifdef CGI_OVERLOAD_DELAY
+               char *request_method = getenv("REQUEST_METHOD");
+               if (request_method && strcmp(request_method, "GET") == 0) {
+                       if (lockf(lockfd, F_TLOCK, 0) == 0) {
+                               set_cgilock_fd(lockfd);
+                       }
+                       else {
+                               printf("Content-Type: text/html\\nRefresh: %i; URL=%s\\n\\n<html><head><title>please wait...</title><head><body><p>Please wait ...</p></body></html>",
+                                       CGI_OVERLOAD_DELAY,
+                                       getenv("REQUEST_URI"));
+                               exit(0);
+                       }
+               }
+               else if (lockf(lockfd, F_LOCK, 0) == 0) {
+                       set_cgilock_fd(lockfd);
+               }
+#else
+               if (lockf(lockfd, F_LOCK, 0) == 0) {
+                       set_cgilock_fd(lockfd);
+               }
+#endif
        }
 EOF
        }
        }
 EOF
        }
@@ -140,6 +171,12 @@ void addenv(char *var, char *val) {
        newenviron[i++]=s;
 }
 
        newenviron[i++]=s;
 }
 
+set_cgilock_fd (int lockfd) {
+       char *fd_s=malloc(8);
+       sprintf(fd_s, "%i", lockfd);
+       setenv("IKIWIKI_CGILOCK_FD", fd_s, 1);
+}
+
 int main (int argc, char **argv) {
        int lockfd=-1;
        char *s;
 int main (int argc, char **argv) {
        int lockfd=-1;
        char *s;
diff --git a/debian/changelog b/debian/changelog
index 8d7618753d96f2bf8fd28930dd08e65d819fd916..842eb680677c0a4c3bddec4397c6632649a41230 100644 (file)
--- a/debian/changelog
+++ b/debian/changelog
@@ -3,6 +3,14 @@ ikiwiki (3.20120726) UNRELEASED; urgency=low
   * monochrome: New theme, contributed by Jon Dowland.
   * rst: Ported to python 3, while still also being valid python 2.
     Thanks, W. Trevor King
   * monochrome: New theme, contributed by Jon Dowland.
   * rst: Ported to python 3, while still also being valid python 2.
     Thanks, W. Trevor King
+  * Try to avoid a situation in which so many ikiwiki cgi wrapper programs
+    are running, all waiting on some long-running thing like a site rebuild,
+    that it prevents the web server from doing anything else. The current
+    approach only avoids this problem for GET requests; if multiple cgi's
+    run GETs on a site at the same time, one will display a "please wait"
+    page for a configurable number of seconds, which then redirects to retry.
+    To enable this protection, set cgi_overload_delay to the number of
+    seconds to wait. This is not enabled by default.
 
  -- Joey Hess <joeyh@debian.org>  Thu, 30 Aug 2012 11:56:12 -0400
 
 
  -- Joey Hess <joeyh@debian.org>  Thu, 30 Aug 2012 11:56:12 -0400
 
Ikiwiki is a compiler for VCS-based (Git, Subversion, ...) wikis.