bench_childprocess.zig

child.zig

const std = @import("std");
pub fn main() !void {
    try std.io.getStdOut().writer().writeAll("hello world\n");
}

parent.zig

const std = @import("std");
const ChildProcess = std.ChildProcess;
const testing = std.testing;
pub fn main() !void {
    var general_purpose_allocator = std.heap.GeneralPurposeAllocator(.{}){};
    defer std.debug.assert(!general_purpose_allocator.deinit());
    const gpa = general_purpose_allocator.allocator();

    var child_proceses: [1_000]ChildProcess = undefined;
    for (child_proceses) |*child_process| {
        child_process.* = ChildProcess.init(
            &[_][]const u8{"./child"},
            gpa,
        );
    }

    for (child_proceses) |*child_process| {
        //try child_process.spawn(null);
        try child_process.spawn();
    }

    for (child_proceses) |*child_process| {
        const ret_val = try child_process.wait();
        try testing.expectEqual(ret_val, .{ .Exited = 0 });
    }
}

shell

zig build-exe -OReleaseFast parent.zig
zig build-exe -OReleaseFast child.zig
time ./parent

round about these values, if repeated sufficiently often:
real    0m0,263s
user    0m0,483s
sys     0m0,332s

With the changes applies (null inserted into spawn function):
real    0m0,255s
user    0m0,471s
sys     0m0,327s

Next: trying to simulate some work