fuzzMultiThreaded

fn fuzzMultiThreaded(ctx: FuzzMultiThreadedContext, smith: *Smith) !void {
    @disableInstrumentation();

    var gpa_instance: std.heap.FixedBufferAllocator = .init(ctx.testing_buf);
    const gpa = gpa_instance.allocator();

    var op_count: u32 = 0;
    while (!smith.eosWeighted(fuzz_probs.eos)) op_count += 1;
    const Op = FuzzMultiThreadedContext.ThreadOps.Op;
    const ops = gpa.alloc(Op, op_count) catch return error.SkipZigTest;
    const op_results = gpa.alloc(Op.MemoryDependency, op_count) catch return error.SkipZigTest;
    @memset(op_results, .init);

    const allocs = gpa.alloc(struct {
        memory: *FuzzMultiThreadedContext.ThreadOps.Op.MemoryDependency,
        alignment: Alignment,
        splat: ?u8,
    }, op_count) catch return error.SkipZigTest;
    var allocs_n: u32 = 0;
    var expected_remaps: usize = 0;

    const options = fuzz_probs.generateOptions(smith);
    for (ops, op_results) |*op, *result| switch (fuzz_probs.generateOp(smith, allocs_n != 0)) {
        .alloc => {
            const splat = fuzz_probs.generateSplat(smith);
            const will_memset = options.check_write_after_free or splat != null;
            op.* = .{ .alloc = .{
                .len = fuzz_probs.generateLen(smith, will_memset),
                .alignment = smith.valueWeighted(Alignment, fuzz_probs.alignment),

                .splat = splat,
                .result = result,
            } };
            allocs[allocs_n] = .{
                .memory = result,
                .alignment = op.alloc.alignment,
                .splat = splat,
            };
            allocs_n += 1;
        },
        .free => {
            const i = smith.valueRangeLessThan(u32, 0, allocs_n);
            op.* = .{ .free = .{
                .memory = allocs[i].memory,
                .alignment = allocs[i].alignment,

                .splat = allocs[i].splat,
            } };

            allocs_n -= 1;
            allocs[i] = allocs[allocs_n];
        },
        .resize, .remap => |kind| {
            op.* = switch (kind) {
                .remap => .{ .remap = undefined },
                .resize => .{ .resize = undefined },
                else => unreachable,
            };
            const realloc = switch (kind) {
                .remap => &op.remap,
                .resize => &op.resize,
                else => unreachable,
            };
            expected_remaps += @intFromBool(kind == .remap);

            const i = smith.valueRangeLessThan(u32, 0, allocs_n);
            realloc.* = .{
                .memory = allocs[i].memory,
                .alignment = allocs[i].alignment,
                .new_len = fuzz_probs.generateLen(smith, options.check_write_after_free),

                .splat = allocs[i].splat,
                .result = result,
            };
            allocs[i].memory = result;
        },
    };

    const fails: []bool = gpa.alloc(bool, ops.len * 2 + smith.value(u8)) catch &.{};
    const fixed_remaps: []bool = gpa.alloc(bool, expected_remaps + smith.value(u8)) catch &.{};
    for (fails) |*f| f.* = smith.boolWeighted(31, 1);
    for (fixed_remaps) |*f| f.* = smith.value(bool);
    var backing_gpa_instance: FuzzMultiThreadedAllocator = .{
        .gpa = gpa,

        .fill = 0,
        .active_allocs = 0,
        .fail_i = 0,
        .fixed_remap_i = 0,

        .buf = ctx.backing_buf,
        .fails = fails,
        .fixed_remaps = fixed_remaps,
    };
    const backing_gpa = backing_gpa_instance.allocator();

    ctx.ops.instance = .init(backing_gpa, options);
    ctx.ops.i = 0;
    ctx.ops.items = ops;

    ctx.ops.running = FuzzMultiThreadedContext.n_threads;
    // Loading `ctx.ops.run` non-atomically is fine since this is the only thread that writes to it.
    @atomicStore(FuzzMultiThreadedContext.ThreadOps.Run, &ctx.ops.run, ctx.ops.run.next(), .release);
    ctx.io.futexWake(FuzzMultiThreadedContext.ThreadOps.Run, &ctx.ops.run, math.maxInt(u32));
    while (true) {
        const prev_running = @atomicLoad(u32, &ctx.ops.running, .acquire);
        if (prev_running == 0) break;
        ctx.io.futexWaitUncancelable(u32, &ctx.ops.running, prev_running);
    }

    var expected_allocs = allocs_n;
    for (allocs[0..allocs_n]) |a| {
        expected_allocs -= @intFromBool(a.memory.memory == null);
    }
    try std.testing.expectEqual(expected_allocs, ctx.ops.instance.deinitLog(false));
    try std.testing.expectEqual(0, backing_gpa_instance.active_allocs); // no leaks
}