Fix error path if realloc call fails.

[ocaml-ancient.git] / ancient.mli

diff --git a/ancient.mli b/ancient.mli
index 50d6c8a..ed3e680 100644 (file)
--- a/ancient.mli
+++ b/ancient.mli
@@ -1,6 +1,4 @@
-(** Mark objects as 'ancient' so they are taken out of the OCaml heap.
-  * $Id: ancient.mli,v 1.3 2006-09-27 18:39:44 rich Exp $
-  *)
+(** Mark objects as 'ancient' so they are taken out of the OCaml heap. *)
 
 type 'a ancient
 
@@ -30,18 +28,43 @@ val delete : 'a ancient -> unit
     * Forgetting to delete an ancient object results in a memory leak.
     *)
 
+val is_ancient : 'a -> bool
+  (** [is_ancient ptr] returns true if [ptr] is an object on the ancient
+    * heap.
+    *)
+
+val address_of : 'a -> nativeint
+  (** [address_of obj] returns the address of [obj], or [0n] if [obj]
+    * is not a block.
+    *)
+
 (** {6 Shared memory mappings} *)
 
 type md
   (** Memory descriptor handle. *)
 
-val attach : Unix.file_descr -> md
-  (** [attach fd] attaches to a new or existing file which may contain
-    * shared objects.
+val attach : Unix.file_descr -> nativeint -> md
+  (** [attach fd baseaddr] attaches to a new or existing file
+    * which may contain shared objects.
     *
     * Initially [fd] should be a read/writable, zero-length file
-    * (see {!Unix.openfile}).  One or more objects can then be
-    * shared in this file using {!Unix.share}.
+    * (for example you could create this using {!Unix.openfile} and
+    * passing the flags [O_RDWR], [O_TRUNC], [O_CREAT]).
+    * One or more objects can then be shared in this file
+    * using {!Unix.share}.
+    *
+    * For new files, [baseaddr] specifies the virtual address to
+    * map the file.  Specifying [Nativeint.zero] ([0n]) here lets [mmap(2)]
+    * choose this, but on some platforms (notably Linux/AMD64)
+    * [mmap] chooses very unwisely, tending to map the memory
+    * just before [libc] with hardly any headroom to grow.  If
+    * you encounter this sort of problem (usually a segfault or
+    * illegal instruction inside libc), then look at [/proc/PID/maps]
+    * and choose a more suitable address.
+    *
+    * If the file was created previously, then the [baseaddr] is
+    * ignored.  The underlying [mmalloc] library will map the
+    * file in at the same place as before.
     *)
 
 val detach : md -> unit
@@ -57,10 +80,8 @@ val share : md -> int -> 'a -> 'a ancient
     * other OCaml processes which can access the underlying
     * file.  See {!Ancient.attach}, {!Ancient.detach}.
     *
-    * More than one object can be stored in a file.  They are
-    * indexed using integers in the range [0..1023] (the limit
-    * is hard-coded in [mmalloc/mmprivate.h]).  The [key] parameter
-    * controls which object is written/overwritten by [share].
+    * More than one object can be stored in a file.  The [key]
+    * parameter controls which object is written/overwritten by [share].
     * If you do not wish to use this feature, just pass [0]
     * as the key.
     *
@@ -72,19 +93,38 @@ val share : md -> int -> 'a -> 'a ancient
     * The underlying [mmalloc] library does not do any sort of
     * locking, so all calls to [share] must ensure that they have
     * exclusive access to the underlying file while in progress.
+    * (Other processes should not even call {!Ancient.get} while
+    * this is happening, but it seems safe to be just reading an
+    * ancient object from the file).
     *)
 
 val get : md -> int -> 'a ancient
   (** [get md key] returns the object indexed by [key] in the
     * attached file.
     *
-    * The key is in the range [0..1023] (the limit is hard-coded in
-    * [mmalloc/mmprivate.h]).
+    * For details of the [key] parameter see {!Ancient.share}.
     *
     * You need to annotate the returned object with the correct
     * type.  As with the Marshal module, there is no type checking,
     * and setting the wrong type will likely cause a segfault
-    * or undefined behaviour.
+    * or undefined behaviour.  Note that the returned object has
+    * type [sometype ancient], not just [sometype].
     *
     * @raises [Not_found] if no object is associated with the key.
     *)
+
+(** {6 Additional information} *)
+
+type info = {
+  i_size : int;                                (** Allocated size, bytes. *)
+}
+  (** Extra information fields.  See {!Ancient.mark_info} and
+    * {!Ancient.share_info}.
+    *)
+
+val mark_info : 'a -> 'a ancient * info
+  (** Same as {!Ancient.mark}, but also returns some extra information. *)
+
+val share_info : md -> int -> 'a -> 'a ancient * info
+  (** Same as {!Ancient.share}, but also returns some extra information. *)
+