Add 07-01 Concurrency

book-src/07-01-spawn.md

@@ -0,0 +1,49 @@
+## Spawn a short-lived thread
+
+The example uses [`std.Thread`] for concurrent and parallel programming.
+[`std.Thread.spawn`] spawns a new thread to calculate the result.
+
+This example splits the array in half and performs the work in separate threads.
+
+```zig
+const std = @import("std");
+
+pub fn main() !void {
+    var arr: [4]i32 = .{ 1, 25, -4, 10 };
+    var max_value: i32 = undefined;
+    try findMax(&max_value, &arr);
+    std.debug.assert(max_value == 25);
+}
+
+fn findMax(max_value: *i32, values: []i32) !void {
+    const THRESHOLD: usize = 2;
+
+    if (values.len == 0) unreachable;
+
+    if (values.len <= THRESHOLD) {
+        var res = values[0];
+        for (values) |it| {
+            res = @max(res, it);
+        }
+        max_value.* = res;
+        return;
+    }
+
+    const mid = values.len / 2;
+    const left = values[0..mid];
+    const right = values[mid..];
+
+    var v1: i32 = undefined;
+    const t1 = try std.Thread.spawn(.{}, findMax, .{ &v1, left });
+    t1.join();
+
+    var v2: i32 = undefined;
+    const t2 = try std.Thread.spawn(.{}, findMax, .{ &v2, right });
+    t2.join();
+
+    max_value.* = @max(v1, v2);
+}
+```
+
+[`std.Thread`]: https://ziglang.org/documentation/0.11.0/std/#A;std:Thread
+[`std.Thread.spawn`]: https://ziglang.org/documentation/0.11.0/std/#A;std:Thread.spawn

book-src/SUMMARY.md

@@ -21,3 +21,6 @@
 
 - [Algorithms]()
   - [Generate Random Values](./06-01-rand.md)
+
+- [Concurrency]()
+  - [Explicit Threads](./07-01-spawn.md)

src/07-01.zig

@@ -0,0 +1,37 @@
+const std = @import("std");
+
+pub fn main() !void {
+    var arr: [4]i32 = .{ 1, 25, -4, 10 };
+    var max_value: i32 = undefined;
+    try findMax(&max_value, &arr);
+    std.debug.assert(max_value == 25);
+}
+
+fn findMax(max_value: *i32, values: []i32) !void {
+    const THRESHOLD: usize = 2;
+
+    if (values.len == 0) unreachable;
+
+    if (values.len <= THRESHOLD) {
+        var res = values[0];
+        for (values) |it| {
+            res = @max(res, it);
+        }
+        max_value.* = res;
+        return;
+    }
+
+    const mid = values.len / 2;
+    const left = values[0..mid];
+    const right = values[mid..];
+
+    var v1: i32 = undefined;
+    const t1 = try std.Thread.spawn(.{}, findMax, .{ &v1, left });
+    t1.join();
+
+    var v2: i32 = undefined;
+    const t2 = try std.Thread.spawn(.{}, findMax, .{ &v2, right });
+    t2.join();
+
+    max_value.* = @max(v1, v2);
+}