1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91

/// A `i64` value used as a message tag.
///
/// Processes can selectively receive messages based on the message's tag. This
/// mechanism can be used to handle messages in a different order from their
/// arrival.
///
/// Creating a new tag will return a process-unique value. Some tag values are
/// reserved for internal use only, but the range from 64 to 128 can be used by
/// the developer to assign application specific meaning.
#[derive(serde::Serialize, serde::Deserialize, Debug, PartialEq, Eq, Clone, Copy, Hash)]
pub struct Tag(i64);

impl Tag {
    /// Create tag of any value.
    pub(crate) fn from(id: i64) -> Tag {
        Tag(id)
    }

    /// Returns a unique tag inside this process.
    ///
    /// Two calls to `Tag::new()` are guaranteed to return a unique tag only if
    /// they occurred inside the same process.
    pub fn new() -> Tag {
        unsafe {
            // Wrap around after 7 bytes. The top byte is reserved for special purposes.
            // Like encoding the handler ID for `AbstractProcesses`.
            COUNTER = (COUNTER + 1) % 0xFFFFFFFFFFFFFF;
            Tag(COUNTER)
        }
    }

    /// Returns a special tag that is used by [`Process::send`](crate::Process).
    ///
    /// Most messages where the order is not significant use this tag.
    pub fn none() -> Tag {
        Tag(0)
    }

    /// Create a special purpose tag.
    ///
    /// The `id` must be in the range between 64 and 128 or the function will
    /// return `None`.
    pub fn special(id: i64) -> Option<Tag> {
        if (64..=128).contains(&id) {
            Some(Tag(id))
        } else {
            None
        }
    }

    pub fn id(&self) -> i64 {
        self.0
    }
}

// Reserve first 128 tags for special purposes.
static mut COUNTER: i64 = 128;

impl Tag {}

impl Default for Tag {
    fn default() -> Self {
        Self::new()
    }
}

#[cfg(test)]
mod tests {
    use lunatic_test::test;

    use super::Tag;

    #[test]
    fn tag_increments() {
        assert_eq!(Tag::new(), Tag(129));
        assert_eq!(Tag::new(), Tag(130));
        assert_eq!(Tag::new(), Tag(131));
        assert_eq!(Tag::new(), Tag(132));
    }

    #[test]
    fn test_special_tag() {
        assert!(Tag::special(64).is_some());
        assert!(Tag::special(128).is_some());

        assert!(Tag::special(63).is_none());
        assert!(Tag::special(129).is_none());

        assert_eq!(Tag::none(), Tag::none());
    }
}