main: Add support for external threads attaching/detaching re context.

This commit allows to create an event loop context and keep a reference
to it in the caller application. After that, this and other threads
are allowed to attach to and detach from this context as needed. Threads
are synchronized by calling re_thread_enter/leave. The re context can
be destroyed by calling mem_deref.

This is useful to allow threads that are not running event loop to
invoke methods on an event loop context that is created and managed by
another thread.

include/re_main.h

@@ -4,6 +4,7 @@
  * Copyright (C) 2010 Creytiv.com
  */
 
+struct re;
 
 enum {
 #ifndef FD_READ
@@ -44,6 +45,10 @@ int   re_main(re_signal_h *signalh);
 void  re_cancel(void);
 int   re_debug(struct re_printf *pf, void *unused);
 
+int  re_alloc(struct re **rep);
+int  re_thread_attach(struct re *re);
+void re_thread_detach(void);
+
 int  re_thread_init(void);
 void re_thread_close(void);
 void re_thread_enter(void);

src/main/main.c

@@ -133,7 +133,7 @@ static void thread_destructor(void *arg)
 }
 
 
-static int re_alloc(struct re **rep)
+int re_alloc(struct re **rep)
 {
 	struct re *re;
 	int err;
@@ -1320,6 +1320,42 @@ void re_thread_leave(void)
 }
 
 
+/**
+ * Attach the current thread to re context
+ */
+int re_thread_attach(struct re *context)
+{
+	struct re *re;
+
+	if (!context)
+		return EINVAL;
+
+	call_once(&flag, re_once);
+
+	re = tss_get(key);
+	if (re) {
+		if (re != context)
+			return EALREADY;
+		return 0;
+	}
+
+	tss_set(key, context);
+
+	return 0;
+}
+
+
+/**
+ * Detach the current thread from re context
+ */
+void re_thread_detach(void)
+{
+	call_once(&flag, re_once);
+
+	tss_set(key, NULL);
+}
+
+
 /**
  * Set an external mutex for this thread
  *