~mdw / dpkg / blame
| Commit | Line | Data |
|---|---|---|
| 1479465f GJ |
1 | Frontend Interfaces |
| 2 | =================== | |
| 3 | ||
| 4 | This file will try to document some of the interfaces that dpkg makes | |
| 5 | available to frontends or that expects them to use, which are currently | |
| 6 | not covered by any other type of documentation. | |
| 7 | ||
| 8 | ||
| 9 | Database Locking | |
| 10 | ---------------- | |
| 11 | ||
| 12 | Any frontend needing to make sure no write operation is currently happening, | |
| 13 | should lock the dpkg database by locking the file «<admindir>/lock» using | |
| 14 | file record locks (i.e. fcntl(2) advisory locking). The whole file should | |
| 15 | be locked, as that's the most portable way to perform this operation; this | |
| 16 | can be achieved by using start=0, len=0 and whence=SEEK_SET. | |
| 17 | ||
| 18 | Take into account there will be a race condition between the frontend | |
| 19 | unlocking the database and the invoked dpkg locking it again, in which | |
| 20 | another process could lock it. | |
| 21 | ||
| 22 | In the future this functionality will be available through a shared libdpkg | |
| 23 | library, and all frontends will be expected to switch to that instead, | |
| 24 | because this will fix the aforementioned race condition. |