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<title>Ocamlnet 4 Reference Manual : Netmcore_heap</title>
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<h1>Module <a href="type_Netmcore_heap.html">Netmcore_heap</a></h1>
<pre><span id="MODULENetmcore_heap"><span class="keyword">module</span> Netmcore_heap</span>: <code class="code">sig</code> <a href="Netmcore_heap.html">..</a> <code class="code">end</code></pre><div class="info module top">
<div class="info-desc">
<p>Shared heaps of structured values</p>
<p>These heaps live in <a href="Netmcore_mempool.html"><code class="code">Netmcore_mempool</code></a>-type shared memory pools,
and can contain an arbitrary number of Ocaml values. These values
can be mutable, but special care has to be taken when modifying them.
The first value pushed onto the heap is called the <i>root element</i>.
All other values must be (directly or indirectly) reachable from the
root element.</p>
<p>Heaps are created with a certain initial size. The heaps remain
connected with the memory pool, and they are enlarged if necessary
by allocating more blocks in the pool.</p>
<p>As the heaps are shared between processes, it must be taken care
that no reference is made from shared heaps to normal process-local
memory. These references would only be valid in the process creating
them, and following such references from other processes would probably
crash the program (or at least return wrong values). In order to ensure
this, it is strictly forbidden to directly manipulate mutable
data structures. The <a href="Netmcore_heap.html#VALmodify"><code class="code">Netmcore_heap.modify</code></a> function has to be used,
as this function makes it possible to copy more values to the heap.
Unfortunately, there is nothing in the type system that would prevent
direct mutation. so this can only be ensured by the discipline of the
programmer.</p>
<p>The values of the heap are also garbage-collected: If all allocated
space is used and more values need to be added, it is first tried
to get rid of old unreachable values. The garbarge collection is done
by the process that happens to initiate the addition of the value
that does no more fit onto the heap. During garbage collection, no
other additions can be done, but read accesses are not prevented.
The garbage collector does not move values (addresses remain unchanged).</p>
<p>The garabage collector only considers values as reachable that are
reachable via the root element. It is not sufficient when a value
is only reachable via a process-specific reference.</p>
</div>
</div>
<hr width="100%">
<pre><span id="TYPEheap"><span class="keyword">type</span> <code class="type">'a</code> heap</span> </pre>
<div class="info ">
<div class="info-desc">
<p>A heap where the type of the root element is <code class="code">'a</code></p>
</div>
</div>
<pre><span id="TYPEdescr"><span class="keyword">type</span> <code class="type">'a</code> descr</span> </pre>
<div class="info ">
<div class="info-desc">
<p>A descriptor ("address") pointing to the heap. Descriptors
can be marshalled.</p>
</div>
</div>
<pre><span id="VALcreate_heap"><span class="keyword">val</span> create_heap</span> : <code class="type"><a href="Netmcore.html#TYPEres_id">Netmcore.res_id</a> -> int -> 'a -> 'a <a href="Netmcore_heap.html#TYPEheap">heap</a></code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">create_heap pool_id size root</code>: Creates a new heap with <code class="code">size</code>
bytes in the pool identified by <code class="code">pool_id</code>. This ID must refer
to a <a href="Netmcore_mempool.html"><code class="code">Netmcore_mempool</code></a>-managed pool.</p>
<p>The value <code class="code">root</code> is copied to the new heap. This is done by
deeply duplicating <code class="code">root</code> and all values pointed to by <code class="code">root</code>,
and storing these duplicates in the heap.</p>
<p>The possible types of value <code class="code">root</code> are restricted, see the <code class="code">add</code>
function for more.</p>
</div>
</div>
<pre><span id="VALminimum_size"><span class="keyword">val</span> minimum_size</span> : <code class="type">'a -> int</code></pre><div class="info ">
<div class="info-desc">
<p>Returns the <code class="code">size</code> value one must pass to <code class="code">create_heap</code> at minimum
to put this root element onto the heap.</p>
</div>
</div>
<pre><span id="VALroot"><span class="keyword">val</span> root</span> : <code class="type">'a <a href="Netmcore_heap.html#TYPEheap">heap</a> -> 'a</code></pre><div class="info ">
<div class="info-desc">
<p>Returns the root element</p>
</div>
</div>
<pre><span id="VALdescr_of_heap"><span class="keyword">val</span> descr_of_heap</span> : <code class="type">'a <a href="Netmcore_heap.html#TYPEheap">heap</a> -> 'a <a href="Netmcore_heap.html#TYPEdescr">descr</a></code></pre><div class="info ">
<div class="info-desc">
<p>Get the descriptor of a heap</p>
</div>
</div>
<pre><span id="VALheap_of_descr"><span class="keyword">val</span> heap_of_descr</span> : <code class="type"><a href="Netmcore.html#TYPEres_id">Netmcore.res_id</a> -> 'a <a href="Netmcore_heap.html#TYPEdescr">descr</a> -> 'a <a href="Netmcore_heap.html#TYPEheap">heap</a></code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">heap_of_descr pool d</code>:
Get the heap for a descriptor. This assumes that the heap still
exists.</p>
</div>
</div>
<pre><span id="TYPEmutator"><span class="keyword">type</span> <code class="type"></code>mutator</span> </pre>
<div class="info ">
<div class="info-desc">
<p>Mutators allow it to push new values onto the heap.</p>
<p>Caveat: pushed values are not considered as roots, and thus they
need immediately be attached to the existing data structure.
Otherwise, the next push might trigger a garbage collection, and
the new value is deleted. If this is not possible, one can
call <code class="code">pin</code> instead (see below).</p>
</div>
</div>
<pre><span id="VALmodify"><span class="keyword">val</span> modify</span> : <code class="type">'a <a href="Netmcore_heap.html#TYPEheap">heap</a> -> (<a href="Netmcore_heap.html#TYPEmutator">mutator</a> -> 'r) -> 'r</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">modify h mutate</code>: This function locks the heap so that this process
has exclusive write access to it for the duration of the <code class="code">mutate</code>
function. The <code class="code">mutate</code> function is immediately called back, and
the argument of <code class="code">mutate</code> is the mutator <code class="code">m</code> that allows one to push
values onto the heap.</p>
<p>By calling <code class="code">add m x</code> from the body of <code class="code">mutate</code> one can create a copy
of <code class="code">x</code> that is stored in the heap.</p>
</div>
</div>
<pre><span id="VALadd"><span class="keyword">val</span> add</span> : <code class="type"><a href="Netmcore_heap.html#TYPEmutator">mutator</a> -> 'a -> 'a</code></pre><div class="info ">
<div class="info-desc">
<p>Pushes a new value onto the heap. This creates a deep copy of the
value.</p>
<p>Not all values can be pushed here. In particular, forbidden are:</p>
<ul>
<li>Functions</li>
<li>Objects</li>
<li>Unsupported custom blocks, e.g. <code class="code">in_channel</code> and <code class="code">out_channel</code>.
Supported custom blocks are only <code class="code">int32</code>, <code class="code">int64</code>, <code class="code">nativeint</code>,
and bigarrays.</li>
<li>Heaps (a heap cannot contain a heap)</li>
<li>Values containing semaphores and other synchronization primitives.
Explicitly allowed are dummy primitives like <a href="Netmcore_mutex.html#VALdummy"><code class="code">Netmcore_mutex.dummy</code></a>.</li>
</ul>
</div>
</div>
<pre><span id="VALadd_immutable"><span class="keyword">val</span> add_immutable</span> : <code class="type"><a href="Netmcore_heap.html#TYPEmutator">mutator</a> -> 'a -> 'a</code></pre><div class="info ">
<div class="info-desc">
<p>Pushes a new value onto the heap. This function must only be used
if the added value is immutable. An important optimization is applied
here: if parts of the value are already living on the heap, these
parts are not copied, but shared with the output value.</p>
<p>The same value restrictions apply as for <code class="code">add</code>. Note that
<code class="code">add_immutable</code> cannot be used if the value to copy lives in a different
heap of the same pool (as a whole or partially). In this case use
<code class="code">add</code>.</p>
</div>
</div>
<pre><span id="VALadd_uniform_array"><span class="keyword">val</span> add_uniform_array</span> : <code class="type"><a href="Netmcore_heap.html#TYPEmutator">mutator</a> -> int -> 'a -> 'a array</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">add_uniform_array m n x</code>: Pushes a new value with n elements onto
the heap. Each index position of the array is initialized with
the same copy of <code class="code">x</code>.</p>
<p>You should not call this function with <code class="code">n=0</code>, because this results in
a copied atom, which is an illegal representation in OCaml.</p>
</div>
</div>
<pre><span id="VALadd_init_array"><span class="keyword">val</span> add_init_array</span> : <code class="type"><a href="Netmcore_heap.html#TYPEmutator">mutator</a> -> int -> (int -> 'a) -> 'a array</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">add_init_array m n f</code>: Pushes a new value with n elements onto
the heap. The index position <code class="code">k</code> is inititialized by running
<code class="code">f k</code> and pushing the copy of this onto the heap.</p>
<p>You should not call this function with <code class="code">n=0</code>, because this results in
a copied atom, which is an illegal representation in OCaml.</p>
</div>
</div>
<pre><span id="VALadd_some"><span class="keyword">val</span> add_some</span> : <code class="type"><a href="Netmcore_heap.html#TYPEmutator">mutator</a> -> 'a -> 'a option</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">add_some mut x</code>: Returns <code class="code">Some x</code> where the O'Caml value representing
<code class="code">Some</code> is allocated in the heap using <code class="code">mut</code>. It is assumed that <code class="code">x</code> is
already a resident of the heap. This means <code class="code">x</code> is not copied!</p>
</div>
</div>
<pre><span id="VALadd_string"><span class="keyword">val</span> add_string</span> : <code class="type"><a href="Netmcore_heap.html#TYPEmutator">mutator</a> -> int -> string</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">let s = add_string mut len</code>: Adds an uninitialized string of length
<code class="code">len</code> to the heap using <code class="code">mut</code>, and returns the string</p>
</div>
</div>
<pre><span id="VALpin"><span class="keyword">val</span> pin</span> : <code class="type"><a href="Netmcore_heap.html#TYPEmutator">mutator</a> -> 'a -> unit</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">pin m x</code>: Pins a shared value <code class="code">x</code> so it cannot be deleted by
the garbage collector. The value remains pinned for the lifetime
of the mutator <code class="code">m</code> (i.e. the runtime of the <code class="code">modify</code> function).</p>
<p>Pinning is relatively expensive if done in masses, and should be
avoided if possible.</p>
</div>
</div>
<pre><span id="VALcopy"><span class="keyword">val</span> copy</span> : <code class="type">'a -> 'a</code></pre><div class="info ">
<div class="info-desc">
<p>Creates a deep copy of the input value, and stores the duplicate
in normal process memory.</p>
</div>
</div>
<pre><span id="VALwith_value"><span class="keyword">val</span> with_value</span> : <code class="type">'a <a href="Netmcore_heap.html#TYPEheap">heap</a> -> (unit -> 'b) -> ('b -> 'c) -> 'c</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">with_value h find process</code>: Logically, this runs
<code class="code">process (find ())</code> and returns the result. While <code class="code">find</code> is being
executed, the heap is write-locked. This returns a value <code class="code">x</code>.
While <code class="code">process</code> is being executed, the value <code class="code">x</code> is temporarily
added to the set of reachable values, so that a parallely running
garbage collection will not delete it.</p>
<p>Note that <code class="code">x</code> <b>must</b> reside in the heap!</p>
<p>Calling <code class="code">modify</code> from <code class="code">find</code> will cause a deadlock. Calling
it from <code class="code">process</code> is allowed.</p>
</div>
</div>
<pre><span id="VALwith_value_2"><span class="keyword">val</span> with_value_2</span> : <code class="type">'a <a href="Netmcore_heap.html#TYPEheap">heap</a> -> (unit -> 'b * 'c) -> ('b * 'c -> 'z) -> 'z</code></pre>
<pre><span id="VALwith_value_3"><span class="keyword">val</span> with_value_3</span> : <code class="type">'a <a href="Netmcore_heap.html#TYPEheap">heap</a> -> (unit -> 'b * 'c * 'd) -> ('b * 'c * 'd -> 'z) -> 'z</code></pre>
<pre><span id="VALwith_value_4"><span class="keyword">val</span> with_value_4</span> : <code class="type">'a <a href="Netmcore_heap.html#TYPEheap">heap</a> -><br> (unit -> 'b * 'c * 'd * 'e) -> ('b * 'c * 'd * 'e -> 'z) -> 'z</code></pre>
<pre><span id="VALwith_value_5"><span class="keyword">val</span> with_value_5</span> : <code class="type">'a <a href="Netmcore_heap.html#TYPEheap">heap</a> -><br> (unit -> 'b * 'c * 'd * 'e * 'f) -> ('b * 'c * 'd * 'e * 'f -> 'z) -> 'z</code></pre><div class="info ">
<div class="info-desc">
<p>Same as <code class="code">with_value</code>, but a tuple of values can be passed down</p>
</div>
</div>
<pre><span id="VALwith_value_n"><span class="keyword">val</span> with_value_n</span> : <code class="type">'a <a href="Netmcore_heap.html#TYPEheap">heap</a> -> (unit -> 'b list) -> ('b list -> 'c) -> 'c</code></pre><div class="info ">
<div class="info-desc">
<p>Same as <code class="code">with_value</code>, but a list of values can be passed down</p>
</div>
</div>
<pre><span id="VALdestroy"><span class="keyword">val</span> destroy</span> : <code class="type">'a <a href="Netmcore_heap.html#TYPEheap">heap</a> -> unit</code></pre><div class="info ">
<div class="info-desc">
<p>Destroys the heap and gives the memory back to the pool</p>
</div>
</div>
<pre><span id="VALgc"><span class="keyword">val</span> gc</span> : <code class="type">'a <a href="Netmcore_heap.html#TYPEheap">heap</a> -> unit</code></pre><div class="info ">
<div class="info-desc">
<p>Lock the heap and do a GC pass</p>
</div>
</div>
<pre><span id="VALpool"><span class="keyword">val</span> pool</span> : <code class="type">'a <a href="Netmcore_heap.html#TYPEheap">heap</a> -> <a href="Netmcore.html#TYPEres_id">Netmcore.res_id</a></code></pre><div class="info ">
<div class="info-desc">
<p>Return the pool ID</p>
</div>
</div>
<pre><span id="VALmut_pool"><span class="keyword">val</span> mut_pool</span> : <code class="type"><a href="Netmcore_heap.html#TYPEmutator">mutator</a> -> <a href="Netmcore.html#TYPEres_id">Netmcore.res_id</a></code></pre><div class="info ">
<div class="info-desc">
<p>Return the pool ID</p>
</div>
</div>
<pre><span id="VALsem_container"><span class="keyword">val</span> sem_container</span> : <code class="type">'a <a href="Netmcore_heap.html#TYPEheap">heap</a> -> <a href="Netsys_sem.html#TYPEcontainer">Netsys_sem.container</a></code></pre><div class="info ">
<div class="info-desc">
<p>Return the semaphore container</p>
</div>
</div>
<pre><span id="VALmut_sem_container"><span class="keyword">val</span> mut_sem_container</span> : <code class="type"><a href="Netmcore_heap.html#TYPEmutator">mutator</a> -> <a href="Netsys_sem.html#TYPEcontainer">Netsys_sem.container</a></code></pre><div class="info ">
<div class="info-desc">
<p>Return the semaphore container</p>
</div>
</div>
<pre><span id="VALdebug_info"><span class="keyword">val</span> debug_info</span> : <code class="type">'a <a href="Netmcore_heap.html#TYPEheap">heap</a> -> string</code></pre><div class="info ">
<div class="info-desc">
<p>Returns a multi-line debug string</p>
</div>
</div>
<h3 id="2_ExampleMutableVariable">Example: Mutable Variable</h3>
<p>This example creates a heap that stores a single value. (This is
available as <a href="Netmcore_ref.html"><code class="code">Netmcore_ref</code></a>.)</p>
<pre class="codepre"><code class="code"> let shared_ref x =
(* The shm version of [ref x] *)
let r = ref x in
let init_size = minimum_size r in
let hp = create_heap pool_id init_size r in
hp
let deref sref =
(* The shm version of [!] *)
!(root sref)
let assign sref x =
(* The shm version of [:=] - however, a copy of x is done *)
modify sref
(fun add ->
(root sref) := add x
)
</code></pre>
<pre><span id="MODULEDebug"><span class="keyword">module</span> <a href="Netmcore_heap.Debug.html">Debug</a></span>: <code class="code">sig</code> <a href="Netmcore_heap.Debug.html">..</a> <code class="code">end</code></pre></body></html>
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