libthreads: cleanup main thread initialization

Create a "thread" for the primary context, rather than handling special logic
for a separate "cleanup" ucontext_t.

diff --git a/libthreads.c b/libthreads.c
index 5ede8d7eafa5a7cf0e32f740434872c5f9c82987..6da8fbf6a6604b89ddaa7286289a88c9105cd1a7 100644 (file)
--- a/libthreads.c
+++ b/libthreads.c
@@ -9,16 +9,45 @@
 #define STACK_SIZE (1024 * 1024)
 
 static struct thread *current;
-static ucontext_t *cleanup;
 
 static void *stack_allocate(size_t size)
 {
        return malloc(size);
 }
 
+static int create_context(struct thread *t)
+{
+       int ret;
+
+       memset(&t->context, 0, sizeof(t->context));
+       ret = getcontext(&t->context);
+       if (ret)
+               return ret;
+
+       /* t->start_routine == NULL means this is our initial context */
+       if (!t->start_routine)
+               return 0;
+
+       /* Initialize new managed context */
+       t->stack = stack_allocate(STACK_SIZE);
+       t->context.uc_stack.ss_sp = t->stack;
+       t->context.uc_stack.ss_size = STACK_SIZE;
+       t->context.uc_stack.ss_flags = 0;
+       t->context.uc_link = &current->context;
+       makecontext(&t->context, t->start_routine, 1, t->arg);
+
+       return 0;
+}
+
+static int create_initial_thread(struct thread *t)
+{
+       memset(t, 0, sizeof(*t));
+       return create_context(t);
+}
+
 int thread_create(struct thread *t, void (*start_routine), void *arg)
 {
-       static int created;
+       static int created = 1;
        ucontext_t local;
 
        DBG();
@@ -30,32 +59,17 @@ int thread_create(struct thread *t, void (*start_routine), void *arg)
        t->arg = arg;
 
        /* Initialize state */
-       getcontext(&t->context);
-       t->stack = stack_allocate(STACK_SIZE);
-       t->context.uc_stack.ss_sp = t->stack;
-       t->context.uc_stack.ss_size = STACK_SIZE;
-       t->context.uc_stack.ss_flags = 0;
-       if (current)
-               t->context.uc_link = &current->context;
-       else
-               t->context.uc_link = cleanup;
-       makecontext(&t->context, t->start_routine, 1, t->arg);
-
-       return 0;
+       return create_context(t);
 }
 
 void thread_start(struct thread *t)
 {
+       struct thread *old = current;
        DBG();
 
-       if (current) {
-               struct thread *old = current;
-               current = t;
-               swapcontext(&old->context, &current->context);
-       } else {
-               current = t;
-               swapcontext(cleanup, &current->context);
-       }
+       current = t;
+       swapcontext(&old->context, &current->context);
+
        DBG();
 }
 
@@ -83,14 +97,14 @@ void user_main()
 
 int main()
 {
-       struct thread t;
-       ucontext_t main_context;
+       struct thread main_thread, user_thread;
 
-       cleanup = &main_context;
+       create_initial_thread(&main_thread);
+       current = &main_thread;
 
-       thread_create(&t, &user_main, NULL);
+       thread_create(&user_thread, &user_main, NULL);
 
-       thread_start(&t);
+       thread_start(&user_thread);
 
        DBG();