Prepare for radical source tree reorganization. zack/build-layout-experiment

All top-level files and directories are moved into a temporary storage
directory, REORG.TODO, except for files that will certainly still
exist in their current form at top level when we're done (COPYING,
COPYING.LIB, LICENSES, NEWS, README), all old ChangeLog files (which
are moved to the new directory OldChangeLogs, instead), and the
generated file INSTALL (which is just deleted; in the new order, there
will be no generated files checked into version control).

1 files changed, 147 insertions, 0 deletions

diff --git a/REORG.TODO/hurd/hurd/userlink.h b/REORG.TODO/hurd/hurd/userlink.h
new file mode 100644
index 0000000000..4946402df5
--- /dev/null
+++ b/REORG.TODO/hurd/hurd/userlink.h
@@ -0,0 +1,147 @@
+/* Support for chains recording users of a resource; `struct hurd_userlink'.
+   Copyright (C) 1994-2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef	_HURD_USERLINK_H
+
+#define	_HURD_USERLINK_H	1
+#include <features.h>
+
+#define __need_NULL
+#include <stddef.h>
+
+#include <hurd/signal.h>
+#include <setjmp.h>
+
+
+/* This structure records a link in two doubly-linked lists.
+   We call these the per-resource user list and the per-thread
+   active-resource list.
+
+   Users of a given resource are recorded by their presence in a list
+   associated with that resource.  A user attaches his own link (in local
+   storage on his stack) to a shared chain at the time he begins using some
+   resource.  When finished with that resource, the user removes his link
+   from the chain.  If his link is the last (there are no other users of
+   the resource), and his chain has been detached from the shared cell (the
+   resource in the cell has been replaced), then the user deallocates the
+   resource that he used.
+
+   All uses of shared resources by a single thread are linked together by
+   its `active-resource' list; the head of this list is stored in the
+   per-thread sigstate structure.  When the thread makes a non-local exit
+   (i.e. longjmp), it will examine its active-resource list, and each link
+   residing in a stack frame being jumped out of will be unlinked from both
+   the resource's user list and the thread's active-resource list, and
+   deallocate the resource if that was the last user link for that resource.
+
+   NOTE: Access to a thread's active-resource list must always be done
+   inside a signal-proof critical section; the functions in this file
+   assume they are called inside a critical section, and do no locking of
+   their own.  Also important: the longjmp cleanup relies on all userlink
+   structures residing on the stack of the using thread.  */
+
+struct hurd_userlink
+  {
+    struct
+      {
+	struct hurd_userlink *next, **prevp;
+      } resource, thread;
+
+    /* This function is called when a non-local exit
+       unwinds the frame containing this link.  */
+    void (*cleanup) (void *cleanup_data, jmp_buf env, int val);
+    void *cleanup_data;
+  };
+
+
+#ifndef _HURD_USERLINK_H_EXTERN_INLINE
+#define _HURD_USERLINK_H_EXTERN_INLINE __extern_inline
+#endif
+
+
+/* Attach LINK to the chain of users at *CHAINP.  */
+
+_HURD_USERLINK_H_EXTERN_INLINE void
+_hurd_userlink_link (struct hurd_userlink **chainp,
+		     struct hurd_userlink *link)
+{
+  struct hurd_userlink **thread_chainp;
+
+  link->resource.next = *chainp;
+  if (link->resource.next)
+    link->resource.next->resource.prevp = &link->resource.next;
+  link->resource.prevp = chainp;
+  *chainp = link;
+
+  /* Also chain it on the current thread's list of active resources.  */
+  thread_chainp = &_hurd_self_sigstate ()->active_resources;
+  link->thread.next = *thread_chainp;
+  if (link->thread.next)
+    link->thread.next->thread.prevp = &link->thread.next;
+  link->thread.prevp = thread_chainp;
+  *thread_chainp = link;
+}
+
+
+/* Detach LINK from its chain.  Returns nonzero iff this was the
+   last user of the resource and it should be deallocated.  */
+
+_HURD_USERLINK_H_EXTERN_INLINE int
+_hurd_userlink_unlink (struct hurd_userlink *link)
+{
+  /* We should deallocate the resource used if this chain has been detached
+     from the cell (and thus has a nil `prevp'), and there is no next link
+     representing another user reference to the same resource. */
+  int dealloc = ! link->resource.next && ! link->resource.prevp;
+
+  /* Remove our link from the chain of current users.  */
+  if (link->resource.prevp)
+    *link->resource.prevp = link->resource.next;
+  if (link->resource.next)
+    link->resource.next->resource.prevp = link->resource.prevp;
+
+  /* Remove our link from the chain of currently active resources
+     for this thread.  */
+  *link->thread.prevp = link->thread.next;
+  if (link->thread.next)
+    link->thread.next->thread.prevp = link->thread.prevp;
+
+  return dealloc;
+}
+
+
+/* Clear all users from *CHAINP.  Call this when the resource *CHAINP
+   protects is changing.  If the return value is nonzero, no users are on
+   the chain and the caller should deallocate the resource.  If the return
+   value is zero, someone is still using the resource and they will
+   deallocate it when they are finished.  */
+
+_HURD_USERLINK_H_EXTERN_INLINE int
+_hurd_userlink_clear (struct hurd_userlink **chainp)
+{
+  if (*chainp == NULL)
+    return 1;
+
+  /* Detach the chain of current users from the cell.  The last user to
+     remove his link from that chain will deallocate the old resource.  */
+  (*chainp)->resource.prevp = NULL;
+  *chainp = NULL;
+  return 0;
+}
+
+#endif	/* hurd/userlink.h */