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//
// Sometimes you want to race multiple tasks and act on whichever
// finishes first. That's what Select is for!
//
// Select is like a Group, but lets you receive individual results
// as tasks complete — one at a time:
//
// const Race = std.Io.Select(union(enum) {
// fast: u32,
// slow: u32,
// });
//
// var buffer: [2]Race.Union = undefined;
// var sel = Race.init(io, &buffer);
//
// sel.async(.fast, fastFn, .{io});
// sel.async(.slow, slowFn, .{io});
//
// const winner = try sel.await(); // returns first completed
// switch (winner) {
// .fast => |val| ...,
// .slow => |val| ...,
// }
// sel.cancelDiscard(); // cancel remaining, discard results
//
// The buffer must be large enough for all tasks that might
// complete before you call cancelDiscard().
//
// Fix this program to receive the winner of the race.
//
const std = @import("std");
const print = std.debug.print;
const RaceResult = std.Io.Select(union(enum) {
hare: []const u8,
tortoise: []const u8,
});
pub fn main(init: std.process.Init) !void {
const io = init.io;
var buffer: [2]RaceResult.Union = undefined;
var sel = RaceResult.init(io, &buffer);
sel.async(.hare, runHare, .{io});
sel.async(.tortoise, runTortoise, .{io});
// Wait for the first finisher.
// What Select method returns the first completed result?
const winner = ???;
switch (winner) {
.hare => |msg| print("Hare: {s}\n", .{msg}),
.tortoise => |msg| print("Tortoise: {s}\n", .{msg}),
}
// Clean up the loser — we don't need their result.
sel.cancelDiscard();
}
fn runHare(io: std.Io) []const u8 {
// The hare is fast — only 1 second!
io.sleep(std.Io.Duration.fromSeconds(1), .awake) catch return "I got canceled!";
return "I'm fast!";
}
fn runTortoise(io: std.Io) []const u8 {
// The tortoise is slow — 10 seconds.
io.sleep(std.Io.Duration.fromSeconds(10), .awake) catch return "I got canceled!";
return "Slow and steady...";
}
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