docs: 增加 threadlocal 讲解

Author: jinzhongjia

course/basic/define-variable.md

@@ -153,3 +153,9 @@ pub usingnamespace @cImport({
 
 > [!IMPORTANT]
 > 初次阅读此处困惑是正常的，后面的概念学习完成后此处自通。
+
+## `threadlocal`
+
+变量可以使用 `threadlocal` 修饰，来使得该变量在不同线程中是不同的示例：
+
+<<<@/code/release/define_variable.zig#threadlocal

course/code/12/define_variable.zig

@@ -146,3 +146,26 @@ const Deconstruct = struct {
         _ = x;
     }
 };
+
+const ThreadLocal = struct {
+    // #region threadlocal
+    const std = @import("std");
+    threadlocal var x: i32 = 1234;
+
+    fn main() !void {
+        const thread1 = try std.Thread.spawn(.{}, testTls, .{});
+        const thread2 = try std.Thread.spawn(.{}, testTls, .{});
+        testTls();
+        thread1.join();
+        thread2.join();
+    }
+
+    fn testTls() void {
+        // 1234
+        std.debug.print("x is {}\n", .{x});
+        x += 1;
+        // 1235
+        std.debug.print("x is {}\n", .{x});
+    }
+    // #endregion threadlocal
+};

course/code/14/define_variable.zig

@@ -146,3 +146,26 @@ const Deconstruct = struct {
         _ = x;
     }
 };
+
+const ThreadLocal = struct {
+    // #region threadlocal
+    const std = @import("std");
+    threadlocal var x: i32 = 1234;
+
+    fn main() !void {
+        const thread1 = try std.Thread.spawn(.{}, testTls, .{});
+        const thread2 = try std.Thread.spawn(.{}, testTls, .{});
+        testTls();
+        thread1.join();
+        thread2.join();
+    }
+
+    fn testTls() void {
+        // 1234
+        std.debug.print("x is {}\n", .{x});
+        x += 1;
+        // 1235
+        std.debug.print("x is {}\n", .{x});
+    }
+    // #endregion threadlocal
+};