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<link title="Regexp" rel="Chapter" href="Regexp.html"><title>Ocamlnet 3 Reference Manual : Netmcore_mempool</title>
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<h1>Module <a href="type_Netmcore_mempool.html">Netmcore_mempool</a></h1>
<pre><span class="keyword">module</span> Netmcore_mempool: <code class="code">sig</code> <a href="Netmcore_mempool.html">..</a> <code class="code">end</code></pre><div class="info">
Memory pools
<p>
A memory pool is a block of shared memory that is set aside for storing
shared data structures. The pool needs to be created before the
worker processes are forked off that are going to use the pool.
The worker processes do not map the pool to some random address,
but rather the processes inherit the pool from the common master
process which ensures that all processes will see the pool at
the same address.
<p>
In order to allow inheritance, the function <a href="Netmcore.html#VALstart"><code class="code">Netmcore.start</code></a>
for starting workers needs to get an additional argument
<code class="code">~inherit_resources</code>. The resource ID of the pool must be put
into this list - otherwise the worker does not get access to
the pool.
<p>
It is not possible to enlarge the pool later (because of the
inheritance method for making the pool accessible). It is advised
to make the pool large enough for all possible data cases, and
to let the user configure this size.<br>
</div>
<hr width="100%">
<pre><span id="EXCEPTIONOut_of_pool_memory"><span class="keyword">exception</span> Out_of_pool_memory</span></pre>
<pre><span id="VALcreate_mempool"><span class="keyword">val</span> create_mempool</span> : <code class="type">?alloc_really:bool -> int -> <a href="Netmcore.html#TYPEres_id">Netmcore.res_id</a></code></pre><div class="info">
Creates the memory pool as shared memory object of the passed size
(rounded up to the next multiple of pages) and returns the resource ID.
<p>
Note that the process calling this function cannot use the pool,
but only worker processes that are forked later. It is possible
to call <code class="code">create_mempool</code> before running <a href="Netmcore.html#VALstartup"><code class="code">Netmcore.startup</code></a>.
<p>
Option <code class="code">alloc_really</code>: On some operating systems (namely Linux)
shared memory is not fully included into the memory bookkeeping
as long as nothing is written into it (so-called
overcommitment). This means that the memory is not reserved, and
when something is written for the first time, it might happen
that the system cannot grant the request. The consequence is a
bus error. By setting <code class="code">alloc_really</code> to true, all allocated
memory pages are immediately written to, and thus the problem is
avoided (or better, if memory is really tight, you get the bus
error now immediately, at least).
<p>
<b>Note that memory pools have kernel persistence! They are not
automatically deleted when the process finishes. Call <code class="code">unlink_mempool</code>
to delete memory pools.</b><br>
</div>
<pre><span id="VALalloc_mem"><span class="keyword">val</span> alloc_mem</span> : <code class="type"><a href="Netmcore.html#TYPEres_id">Netmcore.res_id</a> -> int -> <a href="Netsys_mem.html#TYPEmemory">Netsys_mem.memory</a></code></pre><div class="info">
Allocate memory in this pool. The passed int the size of the
returned <code class="code">memory</code> object. The size is rounded up to the next
multiple of pages.
<p>
Blocks are actually allocated in units of pages.
<p>
Raises <code class="code">Out_of_pool_memory</code> if there is not enough contiguous
space in the pool.<br>
</div>
<pre><span id="VALsize_mem"><span class="keyword">val</span> size_mem</span> : <code class="type"><a href="Netmcore.html#TYPEres_id">Netmcore.res_id</a> -> <a href="Netsys_mem.html#TYPEmemory">Netsys_mem.memory</a> -> int</code></pre><div class="info">
Returns the size of this block, or raises <code class="code">Not_found</code><br>
</div>
<pre><span id="VALsize_mem_at_addr"><span class="keyword">val</span> size_mem_at_addr</span> : <code class="type"><a href="Netmcore.html#TYPEres_id">Netmcore.res_id</a> -> nativeint -> int</code></pre><div class="info">
Returns the size of the block at this address, or raises <code class="code">Not_found</code><br>
</div>
<pre><span id="VALfree_mem"><span class="keyword">val</span> free_mem</span> : <code class="type"><a href="Netmcore.html#TYPEres_id">Netmcore.res_id</a> -> <a href="Netsys_mem.html#TYPEmemory">Netsys_mem.memory</a> -> unit</code></pre><div class="info">
Frees this allocated block<br>
</div>
<pre><span id="VALstats"><span class="keyword">val</span> stats</span> : <code class="type"><a href="Netmcore.html#TYPEres_id">Netmcore.res_id</a> -> int * int * int</code></pre><div class="info">
Returns <code class="code">(total, free, contiguous)</code> where<ul>
<li><code class="code">total</code> is the total size of the pool</li>
<li><code class="code">free</code> is the number of free bytes</li>
<li><code class="code">contiguous</code> is the size of the largest contiguous free block</li>
</ul>
<br>
</div>
<pre><span id="VALdebug_info"><span class="keyword">val</span> debug_info</span> : <code class="type"><a href="Netmcore.html#TYPEres_id">Netmcore.res_id</a> -> string</code></pre><div class="info">
Returns a string describing the allocations etc.<br>
</div>
<pre><span id="VALshm_name"><span class="keyword">val</span> shm_name</span> : <code class="type"><a href="Netmcore.html#TYPEres_id">Netmcore.res_id</a> -> string</code></pre><div class="info">
Returns the name of the shared memory object<br>
</div>
<pre><span id="VALsem_container"><span class="keyword">val</span> sem_container</span> : <code class="type"><a href="Netmcore.html#TYPEres_id">Netmcore.res_id</a> -> <a href="Netsys_sem.html#TYPEcontainer">Netsys_sem.container</a></code></pre><div class="info">
Returns the semaphore container<br>
</div>
<pre><span id="VALunlink_mempool"><span class="keyword">val</span> unlink_mempool</span> : <code class="type"><a href="Netmcore.html#TYPEres_id">Netmcore.res_id</a> -> unit</code></pre><div class="info">
Deletes the persistent objects of this pool<br>
</div>
<pre><span class="keyword">module</span> <a href="Netmcore_mempool.Debug.html">Debug</a>: <code class="code">sig</code> <a href="Netmcore_mempool.Debug.html">..</a> <code class="code">end</code></pre></body></html>
