* For each userland team the kernel creates an area in the userland

address space that is fully locked and marked B_KERNEL_AREA. It can
  thus be accessed by the kernel without additional checks.
* For each userland thread we do create a user_thread structure in that
  area. The structure is accessible from userland via TLS, using the
  private get_user_thread() function.
* Introduced private userland functions [un]defer_signals(). They can be
  used to cheaply disable/re-enable signal delivery. They use the
  user_thread::defer_signals/pending_signals fields which are
  checked/updated by the kernel.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@25451 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/libroot/user_thread.h

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2008, Ingo Weinhold, [email protected].
+ * Distributed under the terms of the MIT License.
+ */
+#ifndef _LIBROOT_USER_THREAD_H
+#define _LIBROOT_USER_THREAD_H
+
+#include <OS.h>
+#include <TLS.h>
+
+#include <tls.h>		/* kernel header */
+
+
+struct user_thread {
+	int32			defer_signals;		// counter; 0 == signals allowed
+	uint32			pending_signals;	// signals that are pending, when
+										// signals are deferred
+	status_t		wait_status;
+};
+
+
+static inline user_thread*
+get_user_thread()
+{
+	return (user_thread*)tls_get(TLS_USER_THREAD_SLOT);
+}
+
+
+static void inline
+defer_signals()
+{
+	get_user_thread()->defer_signals++;
+}
+
+
+static void inline
+undefer_signals()
+{
+	user_thread* thread = get_user_thread();
+	if (--thread->defer_signals == 0 && thread->pending_signals != 0) {
+		// signals shall no longer be deferred -- call a dummy syscall to handle
+		// the pending ones
+		is_computer_on();
+	}
+}
+
+
+#endif	/* _LIBROOT_USER_THREAD_H */