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
|
//
// We've been using io.async() to launch tasks. But there's a
// stronger variant: io.concurrent().
//
// The difference:
//
// io.async():
// * The function MAY run on a separate unit of concurrency,
// or it may run immediately on the caller (synchronously).
// * Never fails — if no concurrency is available, it just
// runs the function right away.
// * More portable, works with all Io backends.
//
// io.concurrent():
// * GUARANTEES a separate unit of concurrency.
// * Can fail with error.ConcurrencyUnavailable if resources
// are exhausted or the backend doesn't support it.
// * Use when you NEED the task to run independently of the
// caller.
//
// What is a "unit of concurrency"? That depends on the backend!
// The Threaded backend uses OS threads. But the Evented backends
// (Uring, Kqueue, Dispatch) use M:N green threads / fibers,
// which can provide concurrency even on a SINGLE OS thread.
// Your code doesn't need to know the difference.
//
// Because concurrent() can fail, you must handle the error:
//
// var future = try io.concurrent(myFn, .{args});
// defer _ = future.cancel(io);
// const result = future.await(io);
//
// Notice the 'try' — that's the key difference in usage!
//
// Fix this program to launch the computation concurrently.
//
const std = @import("std");
const print = std.debug.print;
pub fn main(init: std.process.Init) !void {
const io = init.io;
// Launch with a guaranteed separate unit of concurrency.
// Which Io method guarantees this?
// (Hint: unlike io.async, this one can fail!)
var future = try io.???(compute, .{io});
defer _ = future.cancel(io);
// Note: All breaks in this exercise (using sleep)
// are only necessary for a deterministic result.
io.sleep(std.Io.Duration.fromMilliseconds(100), .awake) catch {};
print("Main continues...\n", .{});
// Wait 1 second for the output order.
io.sleep(std.Io.Duration.fromMilliseconds(200), .awake) catch {};
print("Main done waiting.\n", .{});
const result = future.await(io);
print("Result: {}\n", .{result});
}
fn compute(io: std.Io) u32 {
print("Computing concurrently!\n", .{});
// Simulate some work.
io.sleep(std.Io.Duration.fromMilliseconds(400), .awake) catch return 0;
return 123;
}
|
