Merge pull request 'Improvements for async-io' (#388) from async-improvements into main

Reviewed-on: https://codeberg.org/ziglings/exercises/pulls/388

build.zig

@@ -1180,9 +1180,9 @@ const exercises = [_]Exercise{
     .{
         .main_file = "093_async9.zig",
         .output =
-        \\Main thread continues...
+        \\Computing concurrently!
-        \\Computing on a separate thread!
+        \\Main continues...
-        \\Main thread done waiting.
+        \\Main done waiting.
         \\Result: 123
         , // pay attention to the comma
     },

exercises/085_async.zig

@@ -7,10 +7,11 @@
 // This interface uses a VTable pattern - a struct of function pointers -
 // to abstract over different concurrency backends:
 //
-//   * Threaded  - classic thread-pool based I/O
+//   * Threaded  - thread-pool based I/O
-//   * Uring     - Linux io_uring
+//   * Evented   - chooses the best event-loop backend for your OS:
-//   * Kqueue    - BSD/macOS
+//       * Uring    on Linux (io_uring)
-//   * Dispatch  - macOS Grand Central Dispatch
+//       * Kqueue   on BSD/macOS
+//       * Dispatch on macOS (Grand Central Dispatch)
 //
 // The Io struct itself is tiny:
 //

exercises/086_async2.zig

@@ -6,41 +6,47 @@
 // won't necessarily be available until you call .await() on it:
 //
 //     var future = io.async(someFunction, .{ arg1, arg2 });
-//     // ... do other work here ...
 //     const result = future.await(io);
 //
 // The function *may* run immediately or on another thread -
 // your code doesn't need to care! That's the beauty of the
-// Io abstraction. (In the Threaded backend, if no thread is
+// Io abstraction.
-// available, the function runs synchronously right away and
-// .await() just returns the already-computed result.)
 //
-// io.async() returns a Future(T) where T is the return type
+// IMPORTANT: Every Future MUST be either .await()ed or .cancel()ed.
-// of the function you passed in. Future has two key methods:
+// Failing to do so leaks resources! A safe pattern is:
 //
-//     .await(io)  - block until the result is ready, return it
+//     var future = io.async(myFn, .{});
-//     .cancel(io) - request cancellation, then return the result
+//     defer _ = future.cancel(io);  // safety net
+//     // ... later, if we want the result:
+//     const result = future.await(io);
+//     // (await after cancel is fine — it just returns the result)
+//
+// Both .await() and .cancel() block until the task finishes and
+// return the result. The difference is that .cancel() also
+// requests the task to stop at its next cancellation point.
+// Calling either one more than once is safe — subsequent calls
+// just return a copy of the result.
 //
 // Fix this program so that computeAnswer runs asynchronously
 // and its result is properly awaited.
 //
 const std = @import("std");
+const print = std.debug.print;
 
 pub fn main(init: std.process.Init) !void {
     const io = init.io;
 
     // Launch computeAnswer asynchronously.
-    // io.async() takes a function and a tuple of its arguments.
     var future = io.async(computeAnswer, .{ 6, 7 });
+    defer _ = future.cancel(io); // always clean up!
 
-    // Meanwhile, print something to show we're not blocked.
+    print("Computing... ", .{});
-    std.debug.print("Computing... ", .{});
 
     // Now collect the result. What method on Future gives us
-    // the value, blocking if it isn't ready yet?
+    // the value, blocking until it's ready?
     const answer = future.???(io);
 
-    std.debug.print("The answer is: {}\n", .{answer});
+    print("The answer is: {}\n", .{answer});
 }
 
 fn computeAnswer(a: u32, b: u32) u32 {

exercises/087_async3.zig

@@ -5,20 +5,17 @@
 // them all. The Io backend may run them concurrently:
 //
 //     var f1 = io.async(taskA, .{});
+//     defer _ = f1.cancel(io);
 //     var f2 = io.async(taskB, .{});
-//
+//     defer _ = f2.cancel(io);
-//     // Both tasks may be running now!
 //     const a = f1.await(io);
 //     const b = f2.await(io);
 //
-// There's also io.concurrent() which provides a STRONGER guarantee:
+// Notice the defer pattern: each async call is immediately
-// it ensures the function gets its own unit of concurrency (e.g. a
+// followed by a defer cancel. This ensures cleanup even if
-// real OS thread). But it can fail with error.ConcurrencyUnavailable
+// we return early or hit an error before reaching await.
-// if resources are exhausted.
+// Since await/cancel are idempotent, the defer is harmless
-//
+// if we've already awaited.
-// io.async() is more portable: if no thread is available, it simply
-// runs the function synchronously. This makes it the right default
-// for most code.
 //
 // Fix this program to launch both tasks and collect their results.
 //
@@ -29,12 +26,14 @@ pub fn main(init: std.process.Init) !void {
     const io = init.io;
 
     // Launch both tasks asynchronously.
-    var future_a = io.async(slowAdd, .{ 10, 20 });
+    var future_a = io.async(slowAdd, .{ 1, 2 });
+    defer _ = future_a.cancel(io);
     var future_b = ???(slowMul, .{ 6, 7 });
+    defer _ = future_b.cancel(io);
 
     // Await both results.
     const sum = future_a.await(io);
-    const product = future_b.???(io);
+    const product = future_b.await(io);
 
     print("{} + {} = {}\n", .{ 1, 2, sum });
     print("{} * {} = {}\n", .{ 6, 7, product });

exercises/088_async4.zig

@@ -14,7 +14,7 @@
 //   * Once you call group.async(), you MUST eventually call
 //     group.await() or group.cancel() to release resources.
 //   * group.cancel() requests cancellation on ALL members,
-//     then waits for them to finish.
+//     then blocks until they all finish.
 //
 // Unlike Future, Group tasks don't return values to the caller.
 // They're ideal for parallel work that communicates through
@@ -38,7 +38,7 @@ pub fn main(init: std.process.Init) !void {
 
     // Wait for all tasks to finish.
     // What Group method blocks until all tasks complete?
-    try group.???
+    try group.???(io);
 
     print("All tasks finished!\n", .{});
 }

exercises/089_async5.zig

@@ -5,7 +5,7 @@
 // Every Future has a .cancel() method that:
 //   1. Requests the task to stop (via error.Canceled at the
 //      next "cancellation point")
-//   2. Waits for the task to actually finish
+//   2. BLOCKS until the task actually finishes
 //   3. Returns whatever result the task produced
 //
 // A "cancellation point" is any Io function that can return
@@ -13,7 +13,7 @@
 //
 //     fn myTask(io: std.Io) u32 {
 //         io.sleep(...) catch |err| switch (err) {
-//             error.Canceled => return 0,  // handle gracefully
+//             error.Canceled => return 0,  // error handle
 //         };
 //         return 42;
 //     }
@@ -21,6 +21,11 @@
 // This is fundamentally different from killing a thread -
 // the task gets a chance to clean up and return a value!
 //
+// Remember: both .await() and .cancel() block and return the
+// result. The only difference is that .cancel() also sends
+// the cancellation request. And both are idempotent — calling
+// either one again just returns the same result.
+//
 // Fix this program: the slow task would take 10 seconds,
 // but we cancel it after 1 second. The task should detect
 // the cancellation and return early.
@@ -32,6 +37,7 @@ pub fn main(init: std.process.Init) !void {
     const io = init.io;
 
     var future = io.async(slowTask, .{io});
+    defer _ = future.cancel(io); // safety net
 
     // Wait 1 second, then cancel instead of waiting the full 10.
     io.sleep(std.Io.Duration.fromSeconds(1), .awake) catch {};
@@ -40,7 +46,7 @@ pub fn main(init: std.process.Init) !void {
 
     // We don't want to wait 10 seconds!
     // Which Future method requests cancellation AND returns the result?
-    const result = ???;
+    const result = future.???(io);
 
     print("Task returned: {}\n", .{result});
 }

exercises/090_async6.zig

@@ -23,6 +23,11 @@
 //     }
 //     sel.cancelDiscard();  // cancel remaining, discard results
 //
+// As with all async primitives: tasks spawned in a Select MUST
+// be cleaned up. Use sel.cancel() to get remaining results one
+// by one (for resource cleanup), or sel.cancelDiscard() if you
+// don't need them.
+//
 // The buffer must be large enough for all tasks that might
 // complete before you call cancelDiscard().
 //
@@ -47,7 +52,7 @@ pub fn main(init: std.process.Init) !void {
 
     // Wait for the first finisher.
     // What Select method returns the first completed result?
-    const winner = ???;
+    const winner = try sel.???();
 
     switch (winner) {
         .hare => |msg| print("Hare: {s}\n", .{msg}),

exercises/093_async9.zig

@@ -5,22 +5,29 @@
 // The difference:
 //
 //   io.async():
-//     * The function MAY run on another thread, or it may run
+//     * The function MAY run on a separate unit of concurrency,
-//       immediately on the current thread (synchronously).
+//       or it may run immediately on the caller (synchronously).
-//     * Never fails — if no thread is available, it just runs
+//     * Never fails — if no concurrency is available, it just
-//       the function right away.
+//       runs the function right away.
 //     * More portable, works with all Io backends.
 //
 //   io.concurrent():
-//     * GUARANTEES a separate unit of concurrency (a real thread
+//     * GUARANTEES a separate unit of concurrency.
-//       in the Threaded backend).
 //     * Can fail with error.ConcurrencyUnavailable if resources
 //       are exhausted or the backend doesn't support it.
-//     * Use when you NEED true parallelism.
+//     * Use when you NEED the task to run independently of the
+//       caller.
+//
+// What is a "unit of concurrency"? That depends on the backend!
+// The Threaded backend uses OS threads. But the Evented backends
+// (Uring, Kqueue, Dispatch) use M:N green threads / fibers,
+// which can provide concurrency even on a SINGLE OS thread.
+// Your code doesn't need to know the difference.
 //
 // Because concurrent() can fail, you must handle the error:
 //
 //     var future = try io.concurrent(myFn, .{args});
+//     defer _ = future.cancel(io);
 //     const result = future.await(io);
 //
 // Notice the 'try' — that's the key difference in usage!
@@ -33,25 +40,30 @@ const print = std.debug.print;
 pub fn main(init: std.process.Init) !void {
     const io = init.io;
 
-    // Launch with a guaranteed separate thread.
+    // Launch with a guaranteed separate unit of concurrency.
-    // Which Io method guarantees true concurrency?
+    // Which Io method guarantees this?
     // (Hint: unlike io.async, this one can fail!)
     var future = try io.???(compute, .{io});
+    defer _ = future.cancel(io);
 
-    print("Main thread continues...\n", .{});
+    // Note: All breaks in this excercise (using sleep)
-
+    // are only necessary for a deterministic result.
-    // Wait 100 millisecond so the output order is deterministic.
     io.sleep(std.Io.Duration.fromMilliseconds(100), .awake) catch {};
 
-    print("Main thread done waiting.\n", .{});
+    print("Main continues...\n", .{});
+
+    // Wait 1 second for the output order.
+    io.sleep(std.Io.Duration.fromMilliseconds(200), .awake) catch {};
+
+    print("Main done waiting.\n", .{});
 
     const result = future.await(io);
     print("Result: {}\n", .{result});
 }
 
 fn compute(io: std.Io) u32 {
-    print("Computing on a separate thread!\n", .{});
+    print("Computing concurrently!\n", .{});
     // Simulate some work.
-    io.sleep(std.Io.Duration.fromMilliseconds(200), .awake) catch return 0;
+    io.sleep(std.Io.Duration.fromMilliseconds(400), .awake) catch return 0;
     return 123;
 }

exercises/094_async10.zig

@@ -1,5 +1,5 @@
 //
-// In exercise 088, we learned that cancellation happens at
+// In exercise 089, we learned that cancellation happens at
 // "cancellation points" — any Io function that can return
 // error.Canceled.
 //
@@ -11,7 +11,7 @@
 //
 //     const old = io.swapCancelProtection(.blocked);
 //     defer _ = io.swapCancelProtection(old);
-//
+
 //     // In this block, NO Io function will return error.Canceled.
 //     // The cancel request is held until protection is restored.
 //
@@ -36,9 +36,10 @@ pub fn main(init: std.process.Init) !void {
     const io = init.io;
 
     var future = io.async(importantTask, .{io});
+    defer _ = future.cancel(io);
 
     // Give the task time to start and enter its critical section.
-    io.sleep(std.Io.Duration.fromMilliseconds(300), .awake) catch {};
+    io.sleep(std.Io.Duration.fromMilliseconds(200), .awake) catch {};
 
     // Cancel while the task is in its protected section.
     const result = future.cancel(io);
@@ -50,12 +51,12 @@ fn importantTask(io: std.Io) []const u8 {
 
     // Protect this section from cancellation.
     // What method swaps the cancel protection state?
-    const old = io.???(. blocked);
+    const old = io.???(.blocked);
     defer _ = io.???(old);
 
     // This sleep will NOT return error.Canceled even though
     // we get canceled during it — protection is active!
-    io.sleep(std.Io.Duration.fromMilliseconds(600), .awake) catch |err| switch (err) {
+    io.sleep(std.Io.Duration.fromMilliseconds(300), .awake) catch |err| switch (err) {
         error.Canceled => {
             // This should never happen while protected!
             return "ERROR: canceled during critical section!";

exercises/095_quiz_async.zig

@@ -16,16 +16,17 @@
 // by a grasshopper) and left several bugs. Can you fix them?
 //
 // Here's what the program should do:
-//   1. Three sensor tasks run concurrently, each sending
+//   1. Three sensor tasks send exactly 3 readings each through
-//      exactly 3 readings through a Queue
+//      a Queue
-//   2. A collector task receives readings, protected by a Mutex
+//   2. A collector task receives readings concurrently,
+//      protected by a Mutex
 //   3. After all sensors finish, the queue is closed
 //   4. The final report is written in a cancel-protected section
 //
 // *************************************************************
 // *                A NOTE ABOUT THIS EXERCISE                 *
 // *                                                           *
-// * This quiz uses concepts from exercises 084-093.           *
+// * This quiz uses concepts from exercises 085-094.           *
 // * There are 6 bugs to fix — look for the ???s!              *
 // *                                                           *
 // *************************************************************
@@ -50,8 +51,8 @@ const GardenWeather = struct {
     fn addReading(self: *GardenWeather, io: std.Io, reading: Reading) void {
         // Bug 1: The collector needs to lock before modifying
         // shared state. What Mutex method acquires the lock?
-        self.mutex.lock(io) catch return;
         self.mutex.???(io) catch return;
+        defer self.mutex.unlock(io);
 
         switch (reading.sensor_type) {
             .thermometer => self.temperature = reading.value,
@@ -70,39 +71,40 @@ pub fn main(init: std.process.Init) !void {
     var reading_buf: [8]Reading = undefined;
     var queue: std.Io.Queue(Reading) = .init(&reading_buf);
 
-    // Sensor group: runs all three sensors to completion.
+    // The collector must run concurrently so it can process
+    // readings while the sensors are still sending.
+    // Start it FIRST to ensure its concurrency unit is reserved.
+    //
+    // Bug 2: The collector needs guaranteed concurrency.
+    // What method ensures a separate unit of concurrency?
+    // (Don't forget: it can fail!)
+    var collector_future = try io.???(collector, .{ io, &queue, &weather });
+    defer _ = collector_future.cancel(io);
+
+    // Sensor group: the sensors can use async — they just need
+    // to run, and async is more portable.
     var sensors: std.Io.Group = .init;
 
-    // Start three sensor tasks. They need GUARANTEED concurrency
+    sensors.async(io, sensor, .{ io, &queue, .thermometer, 20 });
-    // since they each simulate real-time measurement.
+    sensors.async(io, sensor, .{ io, &queue, .hygrometer, 60 });
-    //
+    sensors.async(io, sensor, .{ io, &queue, .anemometer, 10 });
-    // Bug 2: io.async doesn't guarantee a separate thread.
-    // Which Io method guarantees true concurrency?
-    // (Don't forget: it can fail, so you need 'try'!)
-    try sensors.???(io, sensor, .{ io, &queue, .thermometer, 20 });
-    try sensors.???(io, sensor, .{ io, &queue, .hygrometer, 60 });
-    try sensors.???(io, sensor, .{ io, &queue, .anemometer, 10 });
-
-    // Collector group: processes readings from the queue.
-    var collectors: std.Io.Group = .init;
-    collectors.async(io, collector, .{ io, &queue, &weather });
 
     // Bug 3: Wait for ALL sensors to finish sending their readings.
     // What Group method blocks until all tasks complete?
-    try sensors.await(io);
+    try sensors.???(io);
-    // try sensors.???(io);
 
     // All sensors done — close the queue so the collector knows
     // there's no more data coming.
     queue.close(io);
 
-    // Wait for the collector to drain the queue.
+    // Wait for the collector to drain the remaining queue.
-    try collectors.await(io);
+    _ = collector_future.await(io);
+    // _ = collector_future.???(io);
 
     // Now write the garden report. This is critical — it must
     // NOT be interrupted, even if something tries to cancel us!
     //
-    // Bug 4: Protect this section from cancellation.
+    // Bug 5: Protect this section from cancellation.
     // What Io method swaps the cancel protection state?
     const old_protection = io.???(.blocked);
     defer _ = io.???(old_protection);
@@ -125,7 +127,7 @@ fn sensor(
             .value = base_value + @as(i32, @intCast(i)),
         };
 
-        // Bug 5: Send the reading into the queue.
+        // Bug 6: Send the reading into the queue.
         // What Queue method sends a single element?
         queue.???(io, reading) catch return;
     }
@@ -163,8 +165,7 @@ fn printGardenReport(weather: *GardenWeather) void {
 //
 // This quiz covered the main async I/O primitives:
 //   io.async()              - launch a task (may run inline)
-//   io.concurrent()         - launch with guaranteed parallelism
+//   io.concurrent()         - guaranteed unit of concurrency
-//   Group.concurrent()      - concurrent tasks in a group
 //   Future.await/cancel     - collect or cancel a single task
 //   Group.async/await/cancel - manage fire-and-forget tasks
 //   Select.async/await      - race tasks, act on first completion
@@ -180,7 +181,8 @@ fn printGardenReport(weather: *GardenWeather) void {
 //   Batch      - submit multiple I/O operations at once
 //
 // The key insight: all of these work through the Io VTable,
-// so your code is portable across backends (Threaded, Uring,
+// so your code is portable across backends — whether Threaded
-// Kqueue, Dispatch) without any changes!
+// (OS thread pool), or Evented (M:N green threads / fibers
+// that can provide concurrency even on a single OS thread).
 //
 // Doctor Zoraptera approves.

patches/patches/085_async.patch

@@ -1,6 +1,6 @@
---- exercises/085_async.zig	2026-04-01 20:40:08.904999609 +0200
+--- exercises/085_async.zig	2026-04-04 16:01:01.509555724 +0200
-+++ answers/085_async.zig	2026-04-01 20:40:05.641933231 +0200
++++ answers/085_async.zig	2026-04-04 16:00:58.541495688 +0200
-@@ -37,7 +37,7 @@
+@@ -38,7 +38,7 @@
  const std = @import("std");
  
  pub fn main(init: std.process.Init) !void {

patches/patches/086_async2.patch

@@ -1,11 +1,11 @@
---- exercises/086_async2.zig	2026-04-03 19:42:15.274532915 +0200
+--- exercises/086_async2.zig	2026-04-05 12:41:11.350626443 +0200
-+++ answers/086_async2.zig	2026-04-03 21:30:18.180019206 +0200
++++ answers/086_async2.zig	2026-04-05 12:42:00.879791167 +0200
-@@ -38,7 +38,7 @@
+@@ -44,7 +44,7 @@
  
      // Now collect the result. What method on Future gives us
-     // the value, blocking if it isn't ready yet?
+     // the value, blocking until it's ready?
 -    const answer = future.???(io);
 +    const answer = future.await(io);
  
-     std.debug.print("The answer is: {}\n", .{answer});
+     print("The answer is: {}\n", .{answer});
  }

patches/patches/087_async3.patch

@@ -1,18 +1,11 @@
---- exercises/087_async3.zig	2026-04-01 22:51:05.540094851 +0200
+--- exercises/087_async3.zig	2026-04-05 16:12:48.317265515 +0200
-+++ answers/087_async3.zig	2026-04-01 22:50:44.579669189 +0200
++++ answers/087_async3.zig	2026-04-05 16:12:52.269343030 +0200
-@@ -29,12 +29,12 @@
+@@ -28,7 +28,7 @@
-     const io = init.io;
- 
      // Launch both tasks asynchronously.
--    var future_a = io.async(slowAdd, .{ 10, 20 });
+     var future_a = io.async(slowAdd, .{ 1, 2 });
+     defer _ = future_a.cancel(io);
 -    var future_b = ???(slowMul, .{ 6, 7 });
-+    var future_a = io.async(slowAdd, .{ 1, 2 });
 +    var future_b = io.async(slowMul, .{ 6, 7 });
+     defer _ = future_b.cancel(io);
  
      // Await both results.
-     const sum = future_a.await(io);
--    const product = future_b.???(io);
-+    const product = future_b.await(io);
- 
-     print("{} + {} = {}\n", .{ 1, 2, sum });
-     print("{} * {} = {}\n", .{ 6, 7, product });

patches/patches/088_async4.patch

@@ -1,10 +1,10 @@
---- exercises/088_async4.zig	2026-04-01 23:17:31.066443941 +0200
+--- exercises/088_async4.zig	2026-04-06 12:22:06.643385622 +0200
-+++ answers/088_async4.zig	2026-04-01 23:17:39.251612131 +0200
++++ answers/088_async4.zig	2026-04-06 12:22:11.820491035 +0200
 @@ -38,7 +38,7 @@
  
      // Wait for all tasks to finish.
      // What Group method blocks until all tasks complete?
--    try group.???
+-    try group.???(io);
 +    try group.await(io);
  
      print("All tasks finished!\n", .{});

patches/patches/089_async5.patch

@@ -1,10 +1,10 @@
---- exercises/089_async5.zig	2026-04-01 23:40:40.505855238 +0200
+--- exercises/089_async5.zig	2026-04-06 14:38:54.443726849 +0200
-+++ answers/089_async5.zig	2026-04-01 23:40:10.176236971 +0200
++++ answers/089_async5.zig	2026-04-06 14:38:39.945438309 +0200
-@@ -40,7 +40,7 @@
+@@ -46,7 +46,7 @@
  
      // We don't want to wait 10 seconds!
      // Which Future method requests cancellation AND returns the result?
--    const result = ???;
+-    const result = future.???(io);
 +    const result = future.cancel(io);
  
      print("Task returned: {}\n", .{result});

patches/patches/090_async6.patch

@@ -1,10 +1,10 @@
---- exercises/090_async6.zig	2026-04-02 10:25:34.016616118 +0200
+--- exercises/090_async6.zig	2026-04-06 18:49:37.232023422 +0200
-+++ answers/090_async6.zig	2026-04-02 10:27:48.827144051 +0200
++++ answers/090_async6.zig	2026-04-06 18:49:22.189720687 +0200
-@@ -47,7 +47,7 @@
+@@ -52,7 +52,7 @@
  
      // Wait for the first finisher.
      // What Select method returns the first completed result?
--    const winner = ???;
+-    const winner = try sel.???();
 +    const winner = try sel.await();
  
      switch (winner) {

patches/patches/093_async9.patch

@@ -1,11 +1,11 @@
---- exercises/093_async9.zig	2026-04-03 13:44:50.526780809 +0200
+--- exercises/093_async9.zig	2026-04-06 19:26:11.388025362 +0200
-+++ answers/093_async9.zig	2026-04-03 13:44:54.957870294 +0200
++++ answers/093_async9.zig	2026-04-06 19:18:36.242931688 +0200
-@@ -36,7 +36,7 @@
+@@ -43,7 +43,7 @@
-     // Launch with a guaranteed separate thread.
+     // Launch with a guaranteed separate unit of concurrency.
-     // Which Io method guarantees true concurrency?
+     // Which Io method guarantees this?
      // (Hint: unlike io.async, this one can fail!)
 -    var future = try io.???(compute, .{io});
 +    var future = try io.concurrent(compute, .{io});
+     defer _ = future.cancel(io);
  
-     print("Main thread continues...\n", .{});
+     // Note: All breaks in this excercise (using sleep)
- 

patches/patches/094_async10.patch

@@ -1,10 +1,10 @@
---- exercises/094_async10.zig	2026-04-03 14:25:16.600025924 +0200
+--- exercises/094_async10.zig	2026-04-06 19:36:59.873966580 +0200
-+++ answers/094_async10.zig	2026-04-03 14:24:56.192615893 +0200
++++ answers/094_async10.zig	2026-04-06 19:37:12.416216872 +0200
-@@ -50,8 +50,8 @@
+@@ -51,8 +51,8 @@
  
      // Protect this section from cancellation.
      // What method swaps the cancel protection state?
--    const old = io.???(. blocked);
+-    const old = io.???(.blocked);
 -    defer _ = io.???(old);
 +    const old = io.swapCancelProtection(.blocked);
 +    defer _ = io.swapCancelProtection(old);

patches/patches/095_quiz_async.patch

@@ -1,38 +1,42 @@
---- exercises/095_quiz_async.zig	2026-04-03 18:04:53.577391455 +0200
+--- exercises/095_quiz_async.zig	2026-04-06 19:55:17.111817364 +0200
-+++ answers/095_quiz_async.zig	2026-04-03 18:05:42.570392172 +0200
++++ answers/095_quiz_async.zig	2026-04-06 19:56:16.063974543 +0200
 @@ -51,7 +51,7 @@
+     fn addReading(self: *GardenWeather, io: std.Io, reading: Reading) void {
          // Bug 1: The collector needs to lock before modifying
          // shared state. What Mutex method acquires the lock?
-         self.mutex.lock(io) catch return;
 -        self.mutex.???(io) catch return;
-+        defer self.mutex.unlock(io);
++        self.mutex.lock(io) catch return;
+         defer self.mutex.unlock(io);
  
          switch (reading.sensor_type) {
-             .thermometer => self.temperature = reading.value,
+@@ -78,7 +78,7 @@
-@@ -79,9 +79,9 @@
+     // Bug 2: The collector needs guaranteed concurrency.
-     // Bug 2: io.async doesn't guarantee a separate thread.
+     // What method ensures a separate unit of concurrency?
-     // Which Io method guarantees true concurrency?
+     // (Don't forget: it can fail!)
-     // (Don't forget: it can fail, so you need 'try'!)
+-    var collector_future = try io.???(collector, .{ io, &queue, &weather });
--    try sensors.???(io, sensor, .{ io, &queue, .thermometer, 20 });
++    var collector_future = try io.concurrent(collector, .{ io, &queue, &weather });
--    try sensors.???(io, sensor, .{ io, &queue, .hygrometer, 60 });
+     defer _ = collector_future.cancel(io);
--    try sensors.???(io, sensor, .{ io, &queue, .anemometer, 10 });
+ 
-+    try sensors.concurrent(io, sensor, .{ io, &queue, .thermometer, 20 });
+     // Sensor group: the sensors can use async — they just need
-+    try sensors.concurrent(io, sensor, .{ io, &queue, .hygrometer, 60 });
+@@ -91,7 +91,7 @@
-+    try sensors.concurrent(io, sensor, .{ io, &queue, .anemometer, 10 });
  
-     // Collector group: processes readings from the queue.
-     var collectors: std.Io.Group = .init;
-@@ -90,7 +90,6 @@
      // Bug 3: Wait for ALL sensors to finish sending their readings.
      // What Group method blocks until all tasks complete?
-     try sensors.await(io);
+-    try sensors.???(io);
--    // try sensors.???(io);
++    try sensors.await(io);
  
      // All sensors done — close the queue so the collector knows
      // there's no more data coming.
-@@ -104,8 +103,8 @@
+@@ -99,15 +99,14 @@
+ 
+     // Wait for the collector to drain the remaining queue.
+     _ = collector_future.await(io);
+-    // _ = collector_future.???(io);
+ 
+     // Now write the garden report. This is critical — it must
+     // NOT be interrupted, even if something tries to cancel us!
      //
-     // Bug 4: Protect this section from cancellation.
+     // Bug 5: Protect this section from cancellation.
      // What Io method swaps the cancel protection state?
 -    const old_protection = io.???(.blocked);
 -    defer _ = io.???(old_protection);
@@ -41,9 +45,9 @@
  
      printGardenReport(&weather);
  }
-@@ -127,7 +126,7 @@
+@@ -129,7 +128,7 @@
  
-         // Bug 5: Send the reading into the queue.
+         // Bug 6: Send the reading into the queue.
          // What Queue method sends a single element?
 -        queue.???(io, reading) catch return;
 +        queue.putOne(io, reading) catch return;