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1Cache algorithm
2===============
3
4Cgit normally returns cached pages when invoked. If there is no cache file, or
5the cache file has expired, it is regenerated. Finally, the cache file is
6printed on stdout.
7
8When it is decided that a cache file needs to be regenerated, an attempt is
9made to create a corresponding lockfile. If this fails, the process gives up
10and uses the expired cache file instead.
11
12When there is no cache file for a request, an attempt is made to create a
13corresponding lockfile. If this fails, the process calls sched_yield(2) before
14restarting the request handling.
15
16In pseudocode:
17
18 name = generate_cache_name(request);
19top:
20 if (!exists(name)) {
21 if (lock_cache(name)) {
22 generate_cache(request, name);
23 unlock_cache(name);
24 } else {
25 sched_yield();
26 goto top;
27 }
28 } else if (expired(name)) {
29 if (lock_cache(name)) {
30 generate_cache(request, name);
31 unlock_cache(name);
32 }
33 }
34 print_file(name);
35
36
37The following options can be set in /etc/cgitrc to control cache behaviour:
38 cache-root: root directory for cache files
39 cache-root-ttl: TTL for the repo listing page
40 cache-repo-ttl: TTL for any repos summary page
41 cache-dynamic-ttl: TTL for pages with symbolic references (not SHA1)
42 cache-static-ttl: TTL for pages with sha1 references
43
44TTL is specified in minutes, -1 meaning "infinite caching".
45
46
47Naming of cache files
48---------------------
49Repository listing: <cachedir>/index.html
50Repository summary: <cachedir>/<repo>/index.html
51Repository subpage: <cachedir>/<repo>/<page>/<querystring>.html
52
53The corresponding lock files have a ".lock" suffix.
54