This program is about the POSIX fork() syscall. Zig favors standard library functions std.process.spawn() and std.process.run() functions instead of using OS specific functions like fork(). The spawn and run functions use appropriate OS specific functions underneath and the code we write can stay OS agnostic. As we already saw the spawn function in blog 13, let's look at run function in this blog. The run function allows the programmer to have more control over the child process than spawn. Lets use it to run another process of the same executable. There are several reasons why one would want to do this.
- Fault isolation
- Security sandboxing
- True hard memory limits
Lets see the code for a program that spins itself up on startup as a worker.
const std = @import("std");
pub fn main(init: std.process.Init) !void {
const allocator = init.arena.allocator();
// defer init.arena.deinit(); not needed as zig will deinit main arena on exit anyway
const args = try init.minimal.args.toSlice(allocator);
if (args.len == 2 and std.mem.eql(u8, args[1], "--worker=true")) {
var buffer: [1024]u8 = undefined;
var file_writer = std.Io.File.Writer.init(.stdout(), init.io, &buffer);
var stdout_writer = &file_writer.interface;
try stdout_writer.print("Printing from worker process...\n\n", .{});
try stdout_writer.flush();
} else {
var buffer: [1024]u8 = undefined;
var file_writer = std.Io.File.Writer.init(.stdout(), init.io, &buffer);
var stdout_writer = &file_writer.interface;
try stdout_writer.print("Printing from main process...\n\n", .{});
try stdout_writer.flush();
const argv = &.{ "./worker__main", "--worker=true" };
_ = try std.process.spawn(init.io, .{ .argv = argv, .stdout = .inherit });
}
}
We can build executable using zig build-exe -O ReleaseSafe worker__main.zig, which will create worker__main. When we execute it using ./worker__main, we ll see
Printing from main process...
Printing from worker process...
Thanks for reading. To be continued.