Coroutine

Coroutine in Melang is time-sharing scheduled in a single thread.

If you use the execution file which is generated by the repository on Github, script files in a same melang command will be executed in one process or even one thread.

e.g.

/*the tasks those behind command name are running in a same thread.*/
$ ./melang a.mln b.mln ...

Besides this way, there is a function named Eval to start a new script task in the current thread to execute a piece of code.

Eval(val, data, in_string, alias);

If in_string is true, val will be the script code, otherwise val is the script file path.

data will be passed to the new script task. If we want to use data in new task, we can use the variable named EVAL_DATA which is a built-in variable added by Eval.

data not support all data types, it just supports:

• integer
• real
• boolean
• nil
• string

alias is the name to be indicated to the new coroutine task, and it can be omitted if it doesn’t need a name.

If val is nil, function will return an array of names of all named coroutines.

e.g.

sys = Import('sys');

Eval('sys = Import('sys'); while (1) {sys.print(EVAL_DATA);}', 'bbb', true);
while (1) {
  sys.print('aaa');
}

The output would be like:

...
aaa
aaa
bbb
bbb
bbb
bbb
bbb
bbb
aaa
...

There is the same problem as shown in preprocess. If val is a file path, it will follow the same rules as include’s.

Melang also provide a function to kill running coroutine task.

Kill(alias);

alias is the name that given by function Eval.

This function always return nil.

Examples

Here are two comprehensive examples of HTTP server. There are some functions which will be introduced in library used in these two examples.

There are two files: server.mln and worker.mln.

Example 1.

Each TCP connection will be handled in an individual coroutine.

/* filename: server.mln */
net = Import('net');
sys = Import('sys');

listenfd = net.tcp_listen('127.0.0.1', '80');
while (1) {
    fd = net.tcp_accept(listenfd);
    sys.print(fd);
    Eval('worker.mln', fd);
}

/* filename: worker.mln */
net = Import('net');
sys = Import('sys');

fd = EVAL_DATA;
ret = net.tcp_recv(fd);
if (ret) {
    net.tcp_send(fd, "HTTP/1.1 200 OK\r\nContent-Length: 1\r\n\r\na\r\n\r\n");
}fi
net.tcp_close(fd);
sys.print('quit');

Now, you can use ab (apache bench) to test.

Example 2.

Create a coroutine pool which has 100 coroutines.

Each TCP will be delivered to a coroutine which is in coroutine pool to be handled.

/* filename: server.mln */
net = Import('net');
mq = Import('mq');

listenfd = net.tcp_listen('127.0.0.1', '80');
for (i = 0; i < 4; ++i) {
    Eval('worker.mln', i);
}
while (1) {
    fd = net.tcp_accept(listenfd);
    mq.send('test', fd);
}

/* filename: worker.mln */
sys = Import('sys');
net = Import('net');
mq = Import('mq');

sys.print(EVAL_DATA);
while (1) {
    fd = mq.recv('test');
    ret = net.tcp_recv(fd);
    if (ret) {
        net.tcp_send(fd, "HTTP/1.1 200 OK\r\nContent-Length: 1\r\n\r\na\r\n\r\n");
    }fi
    net.tcp_close(fd);
}