add threads example

threads/build.zig

@@ -0,0 +1,22 @@
+const std = @import("std");
+
+pub fn build(b: *std.build.Builder) void {
+    const target = b.standardTargetOptions(.{});
+    const optimize = b.standardOptimizeOption(.{});
+
+    {
+        const exe = b.addExecutable(.{
+            .name = "threads-simple",
+            .root_source_file = .{ .path = "main.c" },
+            .optimize = optimize,
+            .target = target
+        });
+        exe.linkLibC();
+
+        const run_cmd = b.addRunArtifact(exe);
+        const run_step = b.step("run", "Run simple program");
+        run_step.dependOn(&run_cmd.step);
+
+        b.installArtifact(exe);
+    }
+}

threads/main.c

@@ -0,0 +1,54 @@
+#include <string.h>
+#include <stdio.h>
+#include <pthread.h>
+
+struct shared_data {
+  pthread_mutex_t mutex;
+  int counter;
+};
+
+struct thread_args {
+  const char *name;
+  struct shared_data *shared;
+};
+
+void *thread_callback(void *p) {
+  struct thread_args *args = p;
+  struct shared_data *data = args->shared;
+
+  for (int i = 0; i < 100000; i++) {
+    if (pthread_mutex_lock(&data->mutex) != 0) {
+      perror("pthread_mutex_lock");
+    }
+
+    data->counter++;
+
+    if (pthread_mutex_unlock(&data->mutex) != 0) {
+      perror("pthread_mutex_unlock");
+    }
+  }
+
+  return NULL;
+}
+
+int main() {
+  struct shared_data shared_data = { 0 };
+
+  if (pthread_mutex_init(&shared_data.mutex, NULL) < 0) {
+    printf("Failed to initialise mutex\n");
+    return -1;
+  }
+
+  pthread_t thread1;
+  struct thread_args args1 = { "Thread 1", &shared_data };
+  pthread_create(&thread1, NULL, thread_callback, &args1);
+
+  pthread_t thread2;
+  struct thread_args args2 = { "Thread 2", &shared_data };
+  pthread_create(&thread2, NULL, thread_callback, &args2);
+
+  pthread_join(thread1, NULL);
+  pthread_join(thread2, NULL);
+
+  printf("Counter is %d\n", shared_data.counter);
+}