Unexpected behavior when performing operations involving multiple window reads

[MMukundi]

Reproduction:

int main() {
    // -- SNIP --
    win.fill(1);
    std::vector<int> result(25);

    // Problem here:
    4*win(1,{0,0},{4,4})*win(1,{0,0},{4,4}) >> result.data();

    win.flush();
    // -- SNIP --
}

Expected behavior:

result[0] == 4

Observed behavior:

result[0] == 64

Temporary solution:

    // Quick fix; add parenthesis around the window operations
    4*(win(1,{0,0},{4,4})*win(1,{0,0},{4,4}))>> result.data();

[sg0]

Good catch, I think this is a bug.

[sg0]

Does 4*win(1,{0,0},{4,4})>> result.data(); evaluate correctly?

[MMukundi]

Oddly, 4*win(1,{0,0},{4,4})>> result.data(); correctly evaluates to 4

[sg0]

And what does win(1,{0,0},{4,4}) >> result.data() return after 4*win(1,{0,0},{4,4})>> result.data();? I'm trying to determine if temporaries are stored in the buffer underlying a window itself.

[MMukundi]

4*win(1,{0,0},{4,4}) = 4
win(1,{0,0},{4,4}) = 1
This is true whether or not there is a synchronization call between the two operations

[sg0]

In shared memory, data can be loaded on another process's memory without relying on synch, especially if data size is small. This is something we must poke into, as in assessing this issue.