When we want to mutate data shared between threads, Mutex(Mutually exclusive flag) must be used to synchronize threads, otherwise the result maybe unexpected.
const std = @import("std");
const Io = std.Io;
const Thread = std.Thread;
const Mutex = Io.Mutex;
const SharedData = struct {
mutex: Mutex,
value: i32,
io: Io,
pub fn updateValue(self: *SharedData, increment: i32) !void {
// Use `tryLock` if you don't want to block
try self.mutex.lock(self.io);
defer self.mutex.unlock(self.io);
for (0..10000) |_| {
self.value += increment;
}
}
};
pub fn main(init: std.process.Init) !void {
const io = init.io;
var shared_data = SharedData{ .mutex = .init, .value = 0, .io = io };
// This block is necessary to ensure that all threads are joined before proceeding.
{
const t1 = try Thread.spawn(.{}, SharedData.updateValue, .{ &shared_data, 1 });
defer t1.join();
const t2 = try Thread.spawn(.{}, SharedData.updateValue, .{ &shared_data, 2 });
defer t2.join();
}
try std.testing.expectEqual(shared_data.value, 30_000);
}