Add thread example.

Also remove reference to pthread_t in the JanetThread structure.

examples/threads.janet

@@ -0,0 +1,18 @@
+(defn worker-main
+  [parent]
+  (def name (thread/receive parent))
+  (for i 0 10
+    (os/sleep 1)
+    (print "thread " name " wakeup no. " i))
+  (thread/send parent :done))
+
+(defn make-worker
+  [name]
+  (-> (thread/new make-image-dict) (thread/send worker-main) (thread/send name)))
+
+(def bob (make-worker "bob"))
+(os/sleep 0.5)
+(def joe (make-worker "joe"))
+
+(thread/receive bob)
+(thread/receive joe)

src/core/thread.c

@@ -192,7 +192,6 @@ static JanetThread *janet_make_thread(JanetThreadShared *shared, JanetTable *dic
     thread->shared = shared;
     thread->kind = who;
     thread->dict = dict;
-    thread->handle = NULL;
     return thread;
 }
 
@@ -213,7 +212,6 @@ static int thread_worker(JanetThreadShared *shared) {
 
     /* Create self thread */
     JanetThread *thread = janet_make_thread(shared, dict, JANET_THREAD_SELF);
-    thread->handle = handle;
     Janet threadv = janet_wrap_abstract(thread);
 
     /* Unmarshal the function */
@@ -251,7 +249,8 @@ static void *janet_pthread_wrapper(void *param) {
 
 static void janet_thread_start_child(JanetThread *thread) {
     JanetThreadShared *shared = thread->shared;
-    int error = pthread_create(&thread->handle, NULL, janet_pthread_wrapper, shared);
+    pthread_t handle;
+    int error = pthread_create(&handle, NULL, janet_pthread_wrapper, shared);
     if (error) {
         thread->shared = NULL; /* Prevent GC from trying to mess with shared memory here */
         janet_shared_destroy(shared);

src/include/janet.h

@@ -956,7 +956,6 @@ struct JanetThreadShared {
     JanetChannel child;
 };
 struct JanetThread {
-    pthread_t handle;
     JanetThreadShared *shared;
     JanetTable *dict;
     enum {