Fastbufs: Clean up exception handling

[libucw.git] / ucw / doc / log.txt

diff --git a/ucw/doc/log.txt b/ucw/doc/log.txt
index 2da50e1e6c9e3a3b5d597c5dbe63a63755b21137..28265f7290af6c4795cb5d85e8736f75df062435 100644 (file)
--- a/ucw/doc/log.txt
+++ b/ucw/doc/log.txt
@@ -82,7 +82,7 @@ Example
        int main(int argc, char **argv)
        {
          log_init(argv[0]);
-         struct log_stream *ls = log_new_file("/var/log/utterances");
+         struct log_stream *ls = log_new_file("/var/log/utterances", 0);
          msg(L_INFO | ls->regnum, "Aye captain, we have a log file");
          msg(L_INFO, "Alas, stderr still works");
          return 0;
@@ -125,3 +125,30 @@ log streams or to syslog is therefore not supported.
 ucw/log.h
 ---------
 !!ucw/log.h
+
+Limiting rate: ucw/tbf.h
+------------------------
+
+LibUCW also offers simple means of limiting the rate of log messages (or of any other
+events) by means of a so called 'Token Bucket Filter.' The idea behind this filter is
+simple: To log a message, we need a token. The available tokens are accumulated in
+a bucket which has a fixed 'filling rate' (the number of tokens arriving in the bucket
+per second, which may be a fractional number) and fixed 'maximum capacity.' The
+bucket receives the tokens continuously with the given rate and when it reaches
+the maximum capacity, the extra tokens are dropped on the floor. When a message
+has to be sent, we take a single token from the bucket and if there wasn't any,
+we drop the message.
+
+The filling rate therefore describes the maximum sustained rate of messages,
+while the bucket capacity tells the filter the maximum length of a short burst,
+which can temporarily exceed the rate.
+
+A general bucket filter is available in `ucw/tbf.h`. The usual way of using it
+to limit logging is to set up a filter hook of a stream which asks the TBF for
+every message. (Remember, though, that if your program is multithreaded, the
+filter hook can be run in multiple threads in parallel, so it has to guard the
+TBF by a lock.) The configuration interface for log streams described above
+is able to attach rate limiters to streams per user's request, so you usually
+need not take any extra care.
+
+!!ucw/tbf.h