added cancelation if nothing found

exercises/093_async9.zig

@@ -33,7 +33,7 @@
 // Let's try a slightly simplified example from signal processing:
 // Suppose we're looking for the beginning of a signal above the noise
 // level. To do this, we compare each entry from beginning to end with
-// the threshold.To speed things up a bit, we split the signal into
+// the threshold. To speed things up a bit, we split the signal into
 // two halves and have two parallel workers search for them.
 // Who finds the beginning first "wins" and thus ends the other one.
 //
@@ -45,8 +45,9 @@ const Io = std.Io;
 const print = std.debug.print;
 
 const SearchResult = struct {
-    worker_id: u8,
-    index: usize,
+    found: bool,
+    worker_id: u8 = 0,
+    index: usize = 0,
 };
 
 pub fn main(init: std.process.Init) !void {
@@ -61,6 +62,7 @@ pub fn main(init: std.process.Init) !void {
     var queue = Io.Queue(SearchResult).init(&buf);
 
     // Launch two workers, each searching half the array.
+    // Remember, we want them to be guaranteed separate units of concurrency.
     var f1 = ???(searchRange, .{ data[0..mid], target, 0, 0, &queue, io });
     defer _ = f1.cancel(io);
 
@@ -70,7 +72,8 @@ pub fn main(init: std.process.Init) !void {
     // Wait for the first result.
     const result = try queue.getOne(io);
 
-    print("Worker {} found signal start over threshold at index {}!\n", .{ result.worker_id, result.index });
+    if (result.found)
+        print("Worker {} found signal start over threshold at index {}!\n", .{ result.worker_id, result.index });
 }
 
 fn searchThreshold(
@@ -87,17 +90,20 @@ fn searchThreshold(
         // all workers would continue until the end.
         io.sleep(Io.Duration.fromMilliseconds(1), .awake) catch return;
 
-        // To test this, you can view the work of the workers
+        // To test this, you can uncomment this to view the work of the workers
         // and then comment out the pause.
         // print("id: {} - val: {}\n", .{ worker_id, val });
 
         if (val >= threshold) {
             queue.putOne(io, .{
+                .found = true,
                 .worker_id = worker_id,
                 .index = base_offset + i,
             }) catch return;
             return;
         }
     }
-}
 
+    // Nothing found
+    queue.putOneUncancelable(io, .{ .found = false }) catch return;
+}

patches/patches/093_async9.patch

@@ -1,9 +1,9 @@
---- exercises/093_async9.zig	2026-04-14 09:50:05.694073287 +0200
-+++ answers/093_async9.zig	2026-04-14 09:49:58.604934765 +0200
-@@ -61,10 +61,10 @@
-     var queue = Io.Queue(SearchResult).init(&buf);
+--- exercises/093_async9.zig	2026-04-14 22:06:23.644776893 +0200
++++ answers/093_async9.zig	2026-04-14 22:06:30.606912044 +0200
+@@ -63,10 +63,10 @@
  
      // Launch two workers, each searching half the array.
+     // Remember, we want them to be guaranteed separate units of concurrency.
 -    var f1 = ???(searchRange, .{ data[0..mid], target, 0, 0, &queue, io });
 +    var f1 = try io.concurrent(searchThreshold, .{ io, data[0..mid], threshold, 0, 0, &queue });
      defer _ = f1.cancel(io);
@@ -13,8 +13,3 @@
      defer _ = f2.cancel(io);
  
      // Wait for the first result.
-@@ -100,4 +100,3 @@
-         }
-     }
- }
--