fuzzMultiThreaded

fn fuzzMultiThreaded(fuzz_init: FuzzContext.Init, smith: *std.testing.Smith) anyerror!void {
    @disableInstrumentation();
    const testing = std.testing;
    const io = fuzz_init.threaded_instance.io();

    fuzz_init.sample_instance.prepareFailures(smith);

    const control_allocator = fuzz_init.control_instance.threadSafeAllocator();
    const sample_child_allocator = fuzz_init.sample_instance.allocator();

    var arena_instance = fuzz_init.arena_state.*.promote(sample_child_allocator);
    defer fuzz_init.arena_state.* = arena_instance.state;

    var ctx: FuzzContext = .init(
        control_allocator,
        arena_instance.allocator(),
    );
    defer ctx.deinit();

    var group: std.Io.Group = .init;
    defer group.cancel(io);

    var n_allocs: usize = 0;
    var n_actions: usize = 0;
    while (!smith.eosWeightedSimple(99, 1) and n_actions < FuzzContext.max_action_count) {
        errdefer comptime unreachable;

        const weights: []const testing.Smith.Weight = if (n_allocs == FuzzContext.max_alloc_count)
            &.{
                .value(FuzzContext.Action, .resize, 1),
                .value(FuzzContext.Action, .remap, 1),
                .value(FuzzContext.Action, .free, 1),
            }
        else
            &.{
                .value(FuzzContext.Action, .resize, 1),
                .value(FuzzContext.Action, .remap, 1),
                .value(FuzzContext.Action, .free, 1),
                .value(FuzzContext.Action, .alloc, 3),
            };
        switch (smith.valueWeighted(FuzzContext.Action, weights)) {
            .alloc => {
                const alloc_index = n_allocs;
                n_allocs += 1;
                ctx.allocs[alloc_index].common.len = .free;
                group.concurrent(io, FuzzContext.doOneAlloc, .{
                    &ctx,
                    nextLen(smith),
                    smith.valueRangeAtMost(
                        Alignment,
                        .@"1",
                        .fromByteUnits(2 * std.heap.page_size_max),
                    ),
                    @fromBackingInt(@intCast(alloc_index)),
                }) catch unreachable;
            },
            .resize => group.concurrent(io, FuzzContext.doOneResize, .{ &ctx, nextLen(smith) }) catch unreachable,
            .remap => group.concurrent(io, FuzzContext.doOneRemap, .{ &ctx, nextLen(smith) }) catch unreachable,
            .free => group.concurrent(io, FuzzContext.doOneFree, .{&ctx}) catch unreachable,
        }
        n_actions += 1;
    }

    try group.await(io);
    try ctx.check(n_allocs);

    // This also covers the `deinit` logic since `free_all` uses it internally.

    const old_capacity = arena_instance.queryCapacity();
    const reset_mode: ResetMode = switch (smith.value(@typeInfo(ResetMode).@"union".tag_type.?)) {
        .free_all => .free_all,
        .retain_capacity => .retain_capacity,
        .retain_with_limit => .{ .retain_with_limit = smith.value(usize) },
    };
    const ok = arena_instance.reset(reset_mode);
    const new_capacity = arena_instance.queryCapacity();
    switch (reset_mode) {
        .free_all => {
            try testing.expect(ok);
            try testing.expectEqual(0, new_capacity);
            fuzz_init.sample_instance.reset();
        },
        .retain_with_limit => |limit| if (ok) try testing.expect(new_capacity <= limit),
        .retain_capacity => if (ok) try testing.expectEqual(old_capacity, new_capacity),
    }

    fuzz_init.control_instance.reset();
}