CODEWITHSUNDEEP
androidcandroid-ndk
Eugene Gr. Philippov
Eugene Gr. Philippov

Reputation: 2092

How to port lockf C call to Android?

Please help us port the lockf C call to Android. A situation is surrounded by #ifndef / #endif lines here: https://github.com/PurpleI2P/i2pd/blob/710a35993db02644f7f28dbee739fe1e7a68a5a5/daemon/UnixDaemon.cpp#L164

I've tried flock as suggested by SO answer [2] but it appears that flock on a local Android (ndk v. 23.2.8568313) is a struct, not a function.

Here [1] there are words about per-process file and directory locking, will now experiment with that...

[1] https://stackoverflow.com/a/10308744/529442

[2] https://stackoverflow.com/a/24170314/529442

Upvotes: 2

Views: 71

Answers (2)

skrueger
skrueger

Reputation: 196

Here is the implementation of lockf in bionic that uses fcntl. It is available in API level >= 24.

Upvotes: 0

Eugene Gr. Philippov
Eugene Gr. Philippov

Reputation: 2092

A working example inspired by a comment by @IanAbbott :

    std::string pidfile="/storage/emulated/0/locktest"; //make sure it's writable for you
    auto pidFH = open(pidfile.c_str(), O_RDWR | O_CREAT, 0600);
    if (pidFH < 0)
    {
        std::cerr << "Could not create locktest file " << pidfile << ": " << strerror(errno) << std::endl;
        return 1;
    }

    struct flock fl;
    fl.l_len = 0;
    fl.l_type = F_WRLCK;
    fl.l_whence = SEEK_SET;
    fl.l_start = 0;

    if (fcntl(pidFH, F_SETLK, &fl) != 0)
    {
        std::cerr << "Could not lock locktest file " << pidfile << ": " << strerror(errno) << std::endl;
        return 2;
    }

A code repository with this example: https://github.com/PurpleI2P/i2pd/pull/2052/commits/8e80a8b06fca685bdef778aae5698de03dd755a5

Upvotes: 0

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