Determine if only one instance is running: Difference between revisions

=={{header|D}}==

===Unix Domain Socket===

Unix domain sockets support another addressing mode, via the so-called abstract namespace. This allows us to bind sockets to names rather than to files. What we get are the following benefits (see page 1175 in The Linux Programming Interface):

* There is no need to worry about possible collisions with existing files in the filesystem.

* There is no socket file to be removed upon program termination.

* We do not need to create a file for the socket at all. This obviates target directory existence, permissions checks, and reduces filesystem clutter. Also, it works in chrooted environments.

All we need is to generate a unique name for our program and pass it as the address when calling bind(). The trick is that instead of specifying a file path as the address, we pass a null byte followed by the name of our choosing (e.g. "\0my-unique-name"). The initial null byte is what distinguishes abstract socket names from conventional Unix domain socket path names, which consist of a string of one or more non-null bytes terminated by a null byte.

Read more here: [https://blog.petrzemek.net/2017/07/24/ensuring-that-a-linux-program-is-running-at-most-once-by-using-abstract-sockets/]

<lang d>import std.socket;

bool is_unique_instance() {

auto socket = new Socket(AddressFamily.UNIX, SocketType.STREAM);

auto addr = new UnixAddress("\0/tmp/myapp.uniqueness.sock");

try {

socket.bind(addr);

return true;

} catch (SocketOSException e) {

return false;

}

}

</lang>