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<h1>Module <a href="type_Netmcore.html">Netmcore</a></h1>
<pre><span id="MODULENetmcore"><span class="keyword">module</span> Netmcore</span>: <code class="code">sig</code> <a href="Netmcore.html">..</a> <code class="code">end</code></pre><div class="info module top">
<div class="info-desc">
<p>Multi-processing for compute jobs</p>
<p>This library allows it to develop parallel algorithms that can take
advantage of multiple CPU cores. It does not use Ocaml's multi-threading
feature because this would implicitly serialize all computations.
Instead, independent processes are created, and the communication
between processes is made as cheap and unproblematic as possible.</p>
<p>Please read <a href="Netmcore_basics.html"><code class="code">Netmcore_basics</code></a> for an introduction into using
this module. There is also <a href="Netmcore_tut.html"><code class="code">Netmcore_tut</code></a> with more advanced
techniques.</p>
<p>Before using this library, it is required to call <a href="Netmcore.html#VALstartup"><code class="code">Netmcore.startup</code></a>.
This turns the current process into the master process. The master
process has only a supervising function, and is responsible for
managing global resources, and for starting further worker processes.</p>
<p>The worker processes can start more workers. This is different from
creating a new thread, though: The new worker does not share memory
with its creator. It is also different from calling <code class="code">Unix.fork</code>,
because new workers are always subprocesses of the master process.
This means it is not initialized with a copy of the state of the
logical creator, but with its real parent process which is always
the master.</p>
<p>Compatibility with multi-threading: You may run into big trouble
when the master process starts further threads (after forking
thread-related resources are in an uncontrolled state). There is
no such problem in the worker processes. In this library,
however, nothing is done to ease the multi-threaded life, so you
should carefully check the compatibility first.</p>
<p><a href="Netmcore.html"><code class="code">Netmcore</code></a> controls the lifetime of certain system resources in
addition to worker processes:</p>
<ul>
<li>Temporary files</li>
<li>Shared memory objects</li>
<li>Named semaphores</li>
</ul>
<p>These objects have kernel persistence, and continue to exist when
the program ends. Because of this, there are two mechanisms to
control the lifetime, and to delete these objects finally: First,
if all using processes terminate normally, an object is deleted.
Second, in order to also catch abnormal terminations, these objects
are also managed by storing their names into an external file
"netplex.pmanage" (in the socket directory). When the program is
started the next time with the same socket directory, the objects
from the previous run are automatically deleted. The second mechanism
can be disabled by setting the</p>
<ul>
<li><code class="code">disable_pmanage</code> parameter for the <a href="Netmcore.html#VALstartup"><code class="code">Netmcore.startup</code></a> call, or by
setting the</li>
<li><code class="code">unlink</code> parameter in the same call. This second option only disables
the deletion, but the management file is updated.</li>
</ul>
</div>
</div>
<hr width="100%">
<h3 id="2_Typesandexceptions">Types and exceptions</h3>
<pre><span id="TYPEres_id"><span class="keyword">type</span> <code class="type"></code>res_id</span> = <code class="type">[ `Resource of int ]</code> </pre>
<div class="info ">
<div class="info-desc">
<p>This tagged integer identifies resources. This variant type will never
be extended.</p>
</div>
</div>
<pre><span id="TYPEprocess_id"><span class="keyword">type</span> <code class="type"></code>process_id</span> = <code class="type">[ `Process of int ]</code> </pre>
<div class="info ">
<div class="info-desc">
<p>This tagged integer identifies processes. This variant type will never
be extended.</p>
<p>Note that the int argument is not the Unix PID, but just a self-generated
identifier that is unique for the lifetime of the program.</p>
</div>
</div>
<pre><span id="TYPEcompute_resource_type"><span class="keyword">type</span> <code class="type"></code>compute_resource_type</span> = <code class="type">[ `File<br> | `Fork_point<br> | `Join_point<br> | `Posix_sem<br> | `Posix_shm<br> | `Posix_shm_preallocated<br> | `Posix_shm_preallocated_sc<br> | `Posix_shm_sc ]</code> </pre>
<pre><span id="TYPEinherit_request"><span class="keyword">type</span> <code class="type"></code>inherit_request</span> = <code class="type">[ `All | `Resources of <a href="Netmcore.html#TYPEres_id">res_id</a> list ]</code> </pre>
<pre><span id="TYPEcompute_resource_repr"><span class="keyword">type</span> <code class="type"></code>compute_resource_repr</span> = <code class="type">[ `File of string<br> | `Fork_point of<br> <a href="Netmcore.html#TYPEinherit_request">inherit_request</a> * <a href="Netplex_encap.html#TYPEencap">Netplex_encap.encap</a> -> <a href="Netmcore.html#TYPEprocess_id">process_id</a><br> | `Join_point of <a href="Netmcore.html#TYPEprocess_id">process_id</a> -> <a href="Netplex_encap.html#TYPEencap">Netplex_encap.encap</a> option<br> | `Posix_sem of string<br> | `Posix_shm of string<br> | `Posix_shm_preallocated of string * <a href="Netsys_mem.html#TYPEmemory">Netsys_mem.memory</a><br> | `Posix_shm_preallocated_sc of<br> string * <a href="Netsys_mem.html#TYPEmemory">Netsys_mem.memory</a> * <a href="Netsys_sem.html#TYPEcontainer">Netsys_sem.container</a><br> | `Posix_shm_sc of string * <a href="Netsys_sem.html#TYPEprefix">Netsys_sem.prefix</a> ]</code> </pre>
<div class="info ">
<div class="info-desc">
<p>Centrally managed resources include:</p>
<ul>
<li><code class="code">`File name</code>: (Temporary) file <code class="code">name</code> (absolute name)</li>
<li><code class="code">`Posix_shm name</code>: Shared memory objects with <code class="code">name</code></li>
<li><code class="code">`Posix_shm_sc(name,p)</code>: Shared memory objects with <code class="code">name</code>, and
attached container for semaphores with prefix <code class="code">p</code></li>
<li><code class="code">`Posix_shm_preallocated(name,m)</code>: Shared memory objects already
allocated by the master process. These objects are passed over
to the worker processes by inheritance, and are always mapped at
the same address. <code class="code">m</code> is the bigarray mapping the object.</li>
<li><code class="code">`Posix_shm_preallocated_sc(name,m.p)</code>: Same, plus attached
container for semaphores with prefix <code class="code">p</code></li>
<li><code class="code">`Posix_sem name</code>: Semaphores with <code class="code">name</code></li>
<li><code class="code">`Fork_point(inh,f)</code>: Fork points where <code class="code">let pid=f arg</code> fork a new process
with argument <code class="code">arg</code>. <code class="code">pid</code> is the process identifier. The list <code class="code">inh</code>
are resources inherited from the master.</li>
<li><code class="code">`Joint_point f</code>: Joint points where <code class="code">let res=f pid</code> wait until
the process <code class="code">pid</code> terminates. If <code class="code">res</code> is non-<code class="code">None</code> it is the
result value. If it is <code class="code">None</code>, no result was passed back
(including all pathological cases like crashes)</li>
</ul>
<p>Except fork and join points, these resources are also added to
the pmanage object of Netplex (see <a href="Netplex_cenv.html#VALpmanage"><code class="code">Netplex_cenv.pmanage</code></a> and
<a href="Netsys_pmanage.html"><code class="code">Netsys_pmanage</code></a>).</p>
</div>
</div>
<pre><span id="EXCEPTIONNo_resource"><span class="keyword">exception</span> No_resource</span> <span class="keyword">of</span> <code class="type"><a href="Netmcore.html#TYPEres_id">res_id</a></code></pre>
<div class="info ">
<div class="info-desc">
<p>No such resource, or no resource of the expected type</p>
</div>
</div>
<pre><span id="TYPEcompute_resource"><span class="keyword">class type</span> <a href="Netmcore.compute_resource-c.html">compute_resource</a></span> = <code class="code">object</code> <a href="Netmcore.compute_resource-c.html">..</a> <code class="code">end</code></pre><h3 id="2_Definingprocesses">Defining processes</h3><p>This is the lower-level version of the process API where arguments
and results of processes are dynamically typed. It may have some
uses when writing generic process managers, but for the
normal application the statically typed API in <a href="Netmcore_process.html"><code class="code">Netmcore_process</code></a>
is easier to use (and less verbose).</p>
<pre><span id="VALdef_process"><span class="keyword">val</span> def_process</span> : <code class="type">(<a href="Netplex_encap.html#TYPEencap">Netplex_encap.encap</a> -> <a href="Netplex_encap.html#TYPEencap">Netplex_encap.encap</a>) -><br> <a href="Netmcore.html#TYPEres_id">res_id</a> * <a href="Netmcore.html#TYPEres_id">res_id</a></code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">let fork_point, join_point = def_process f</code>:
Defines process types, i.e. ways of starting and finishing processes.
The definition must be done in the master process, e.g. before the first
worker is started.</p>
<p>Once the process type is defined, new processes can be started,
and these processes will run the function <code class="code">f</code>. When <code class="code">f</code> is
finished, the process will terminate. Starting processes is possible
from other worker processes.</p>
<p><code class="code">f</code> is supplied with its argument by the process starter <code class="code">start</code>.
The result value of <code class="code">f</code> can be retrieved with <code class="code">join</code> (by any
process, but only the first <code class="code">join</code> for this process will be successful).</p>
<p>If <code class="code">f</code> throws exceptions, these will be caught and logged, but not
be passed back to the caller (which just gets <code class="code">None</code> as result
of <code class="code">join</code>). The same happens for any unplanned termination of the
process.</p>
<p>It is allowed to immediately release the <code class="code">join_point</code> if there is
no interest in catching the termination of started processes.</p>
<p>Here is an example how to define a process that takes a <code class="code">string</code>
argument and returns an <code class="code">int</code>:</p>
<pre class="codepre"><code class="code"> module String_encap = Netplex_encap.Make_encap(struct type t=string end)
module Int_encap = Netplex_encap.Make_encap(struct type t=int end)
let my_process_fork, my_process_join =
Netmcore.def_process
(fun s_encap ->
let (s:string) = String_encap.unwrap s_encap in
let (r:int) = ... in
Int_encap.wrap r
)
</code></pre>
<p>The wrapping and unwrapping is required for ensuring type-safety
(see <a href="Netplex_encap.html"><code class="code">Netplex_encap</code></a> for the details of the idea).</p>
<p>Calling this process is done with (also see below):</p>
<pre class="codepre"><code class="code"> let pid = Netmcore.start my_process_fork (String_encap.wrap s) in
let r_encap_opt = Netmcore.join my_process_join pid in
match r_encap_opt with
| None -> failwith "Something went wrong"
| Some r_encap -> Int_encap.unwrap r_encap
</code></pre></div>
</div>
<p>The following functions can also be called from worker processes
(i.e. Netplex containers)</p>
<pre><span id="VALstart"><span class="keyword">val</span> start</span> : <code class="type">?inherit_resources:<a href="Netmcore.html#TYPEinherit_request">inherit_request</a> -><br> <a href="Netmcore.html#TYPEres_id">res_id</a> -> <a href="Netplex_encap.html#TYPEencap">Netplex_encap.encap</a> -> <a href="Netmcore.html#TYPEprocess_id">process_id</a></code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">let pid = start fork_point arg</code>: Starts the process with the
given <code class="code">fork_point</code> and the argument <code class="code">arg</code>.</p>
<p>Raises <code class="code">No_resource</code> if there is no such resource.</p>
<p>The function returns a process identifier. This is not the Unix
PID, but a sequentially generated number that is unique for a
running program.</p>
<p>Option <code class="code">inherit_resources</code>: Certain resources are only accessible by
the process when they are inherited to it. This is the case for
<code class="code">`Posix_shm_preallocated</code>. This can be set to <code class="code">`All</code> to inherit
all inheritable resources, or to <code class="code">`Resources l</code> to only inherit
the resources of <code class="code">l</code>. By default, all resources are inherited.
(This changed in Ocamlnet-3.5 - before, no resources were inherited,
which turned out to be quite dangerous as default.)</p>
</div>
</div>
<pre><span id="VALjoin"><span class="keyword">val</span> join</span> : <code class="type"><a href="Netmcore.html#TYPEres_id">res_id</a> -> <a href="Netmcore.html#TYPEprocess_id">process_id</a> -> <a href="Netplex_encap.html#TYPEencap">Netplex_encap.encap</a> option</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">let res_opt = join join_point pid</code>: Waits until the process <code class="code">pid</code>
is done, and returns the result value if any. You can only join
(or <code class="code">join_nowait</code>) once per process.</p>
<p>Raises <code class="code">No_resource</code> if there is no such resource.</p>
<p>It is not possible to call <code class="code">join</code> from the master process (as this
process must not block). You can, however, get the result of an
already terminated process with <code class="code">join_nowait</code>, e.g. after
<a href="Netmcore.html#VALrun"><code class="code">Netmcore.run</code></a> returned.</p>
</div>
</div>
<pre><span id="VALjoin_nowait"><span class="keyword">val</span> join_nowait</span> : <code class="type"><a href="Netmcore.html#TYPEres_id">res_id</a> -> <a href="Netmcore.html#TYPEprocess_id">process_id</a> -> <a href="Netplex_encap.html#TYPEencap">Netplex_encap.encap</a> option</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">let res_opt = join_nowait join_point pid</code>: Checks if the process <code class="code">pid</code>
is done, and returns the result value if so. Otherwise return <code class="code">None</code>.</p>
</div>
</div>
<h3 id="2_Managingresourcesfromworkerprocesses">Managing resources from worker processes</h3><p>The following functions can also be called from worker processes
(i.e. Netplex containers)</p>
<pre><span id="VALget_resource"><span class="keyword">val</span> get_resource</span> : <code class="type"><a href="Netmcore.html#TYPEres_id">res_id</a> -> <a href="Netmcore.compute_resource-c.html">compute_resource</a></code></pre><div class="info ">
<div class="info-desc">
<p>Retrieves the resource by ID. This implicitly also marks this resource
as being used by this process. Don't forget to call <code class="code">release</code> when
your are done with the resource.</p>
<p>Raises <code class="code">No_resource</code> if there is no such resource.</p>
</div>
</div>
<pre><span id="VALrelease"><span class="keyword">val</span> release</span> : <code class="type"><a href="Netmcore.html#TYPEres_id">res_id</a> -> unit</code></pre><div class="info ">
<div class="info-desc">
<p>Release the resource with this ID. (Same as calling the <code class="code">release</code>
method on the object.)</p>
</div>
</div>
<pre><span id="VALmanage_file"><span class="keyword">val</span> manage_file</span> : <code class="type">string -> <a href="Netmcore.compute_resource-c.html">compute_resource</a></code></pre><div class="info ">
<div class="info-desc">
<p>hands over a file to the manager</p>
</div>
</div>
<pre><span id="VALget_file"><span class="keyword">val</span> get_file</span> : <code class="type"><a href="Netmcore.html#TYPEres_id">res_id</a> -> string</code></pre><div class="info ">
<div class="info-desc">
<p>Gets the file with this ID (or raises <code class="code">No_resource</code>). As for
<code class="code">get_resource</code> the file is marked as being used by the process.</p>
</div>
</div>
<pre><span id="VALmanage_shm"><span class="keyword">val</span> manage_shm</span> : <code class="type">string -> <a href="Netmcore.compute_resource-c.html">compute_resource</a></code></pre><div class="info ">
<div class="info-desc">
<p>hands over a named shm object to the manager</p>
</div>
</div>
<pre><span id="VALmanage_shm_sc"><span class="keyword">val</span> manage_shm_sc</span> : <code class="type">string -> <a href="Netsys_sem.html#TYPEcontainer">Netsys_sem.container</a> -> <a href="Netmcore.compute_resource-c.html">compute_resource</a></code></pre><div class="info ">
<div class="info-desc">
<p>hands over a named shm object plus semaphore container to the manager</p>
</div>
</div>
<pre><span id="VALget_shm"><span class="keyword">val</span> get_shm</span> : <code class="type"><a href="Netmcore.html#TYPEres_id">res_id</a> -> string</code></pre><div class="info ">
<div class="info-desc">
<p>Gets the shm object with this ID (or raises <code class="code">No_resource</code>). As
for <code class="code">get_resource</code> the shm object is marked as being used by the process.</p>
</div>
</div>
<pre><span id="VALget_sem_container"><span class="keyword">val</span> get_sem_container</span> : <code class="type"><a href="Netmcore.html#TYPEres_id">res_id</a> -> <a href="Netsys_sem.html#TYPEcontainer">Netsys_sem.container</a></code></pre><div class="info ">
<div class="info-desc">
<p>Get the semaphore container</p>
</div>
</div>
<p>Shared memory objects can be created with <a href="Netsys_posix.html#VALshm_create"><code class="code">Netsys_posix.shm_create</code></a>,
and opened with <a href="Netsys_posix.html#VALshm_open"><code class="code">Netsys_posix.shm_open</code></a>.</p>
<pre><span id="VALcreate_preallocated_shm"><span class="keyword">val</span> create_preallocated_shm</span> : <code class="type">?value_area:bool -> string -> int -> <a href="Netmcore.html#TYPEres_id">res_id</a> * string</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">create_preallocated_shm prefix size</code>: Creates a new preallocated
shm object with a unique name based on <code class="code">prefix</code>, and a length of
<code class="code">size</code> bytes. The object is created and mapped into the master
process, and will be available to any newly started process when
the resource ID is inherited to the process.</p>
<p>Returns <code class="code">(res_id,shm_name)</code> where <code class="code">res_id</code> identifies the new
resource, and <code class="code">shm_name</code> is the name of the POSIX shared memory
object.</p>
<p>Note that the process calling this function cannot look up this
resource (using <code class="code">get_shm</code> or <code class="code">get_resource</code>) because the shm
block cannot be mapped at the right address. Nevertheless, the calling
process counts as a user of the object, and needs to release
the object.</p>
<p>Option <code class="code">value_area</code>: if set, the new memory is marked as value
area, so the ocaml runtime allows value comparisons in this
memory area.</p>
</div>
</div>
<pre><span id="VALcreate_preallocated_shm_sc"><span class="keyword">val</span> create_preallocated_shm_sc</span> : <code class="type">?value_area:bool -><br> string -> int -> <a href="Netmcore.html#TYPEres_id">res_id</a> * string * <a href="Netsys_sem.html#TYPEcontainer">Netsys_sem.container</a></code></pre><div class="info ">
<div class="info-desc">
<p>Same as <code class="code">create_preallocated_shm</code> with the extension that
a semaphore container is also allocated and returned</p>
</div>
</div>
<pre><span id="VALmanage_sem"><span class="keyword">val</span> manage_sem</span> : <code class="type">string -> <a href="Netmcore.compute_resource-c.html">compute_resource</a></code></pre><div class="info ">
<div class="info-desc">
<p>hands over a named semaphore to the manager</p>
</div>
</div>
<pre><span id="VALget_sem"><span class="keyword">val</span> get_sem</span> : <code class="type"><a href="Netmcore.html#TYPEres_id">res_id</a> -> string</code></pre><div class="info ">
<div class="info-desc">
<p>gets the semaphore with this ID (or raises <code class="code">No_resource</code>). As
for <code class="code">get_resource</code> the semaphore is marked as being used by the process.</p>
</div>
</div>
<p>Semaphores can be opened with <a href="Netsys_posix.html#VALsem_open"><code class="code">Netsys_posix.sem_open</code></a>, and
created with <a href="Netsys_posix.html#VALsem_create"><code class="code">Netsys_posix.sem_create</code></a>.</p>
<pre><span id="VALself_process_id"><span class="keyword">val</span> self_process_id</span> : <code class="type">unit -> <a href="Netmcore.html#TYPEprocess_id">process_id</a></code></pre><div class="info ">
<div class="info-desc">
<p>Returns the process ID of a worker</p>
</div>
</div>
<h3 id="2_Initializationandsystemstart">Initialization and system start</h3><p>This module can either be used as Netplex plugin and integrated into
any existing Netplex program, or it can be started in stand-alone mode</p>
<pre><span id="VALadd_plugins"><span class="keyword">val</span> add_plugins</span> : <code class="type"><a href="Netplex_types.controller-c.html">Netplex_types.controller</a> -> unit</code></pre><div class="info ">
<div class="info-desc">
<p>To enable compute processes for any Netplex program, call this
function with the controller object as argument. This can e.g.
be done in the <code class="code">post_add_hook</code> of the processor.</p>
</div>
</div>
<pre><span id="VALstartup"><span class="keyword">val</span> startup</span> : <code class="type">socket_directory:string -><br> ?pidfile:string -><br> ?init_ctrl:(<a href="Netplex_types.controller-c.html">Netplex_types.controller</a> -> unit) -><br> ?disable_pmanage:bool -><br> ?no_unlink:bool -> first_process:('a -> <a href="Netmcore.html#TYPEprocess_id">process_id</a>) -> 'a -> unit</code></pre><div class="info ">
<div class="info-desc">
<p>This function makes the current process the master process.
It starts immediately a new worker process, called the
first process. The <code class="code">startup</code> function returns first when this
process is finished, in which case the whole Netplex system is
shut down (which may lead to killing the remaining processes,
following the usual shutdown procedure).</p>
<p>The first process is created by calling <code class="code">first_process</code> at the
right moment. This function normally just invokes <code class="code">start</code>.</p>
<p>Passing a <code class="code">socket_directory</code> is mandatory. This directory will
contain helper files. The must be a separate <code class="code">socket_directory</code>
for each running Computeplex instance.</p>
<p><code class="code">pidfile</code>: If passed, the Unix PID of the master process is written
to this file.</p>
<p><code class="code">disable_pmanage</code>: Disable that persistent kernel objects are
managed via the "netplex.pmanage" file in the socket directory.</p>
<p><code class="code">no_unlink</code>: Disable that old persistent kernel objects are deleted at
startup. This may be useful when <code class="code">startup</code> is called a second time
from the same program.</p>
</div>
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<pre><span id="VALrun"><span class="keyword">val</span> run</span> : <code class="type">socket_directory:string -><br> ?pidfile:string -><br> ?init_ctrl:(<a href="Netplex_types.controller-c.html">Netplex_types.controller</a> -> unit) -><br> ?disable_pmanage:bool -><br> ?no_unlink:bool -><br> first_process:('a -> <a href="Netmcore.html#TYPEprocess_id">process_id</a>) -><br> extract_result:(<a href="Netplex_types.controller-c.html">Netplex_types.controller</a> -> <a href="Netmcore.html#TYPEprocess_id">process_id</a> -> 'b) -><br> 'a -> 'b</code></pre><div class="info ">
<div class="info-desc">
<p>This function fixes a design error in <code class="code">startup</code>, namely that it was
difficult to get the result of the process(es) back. Here, the
additional callback <code class="code">extract_result</code> can be used to retrieve the
results from processes, especially from the first process.</p>
<p>You need to call <a href="Netmcore.html#VALjoin_nowait"><code class="code">Netmcore.join_nowait</code></a> to get the results from
processes.</p>
<p>The result of <code class="code">extract_result</code> is the result of <code class="code">run</code>.</p>
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<pre><span id="VALdestroy_resources"><span class="keyword">val</span> destroy_resources</span> : <code class="type">unit -> unit</code></pre><div class="info ">
<div class="info-desc">
<p>Destroys all resources that may be left</p>
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<pre><span id="MODULEDebug"><span class="keyword">module</span> <a href="Netmcore.Debug.html">Debug</a></span>: <code class="code">sig</code> <a href="Netmcore.Debug.html">..</a> <code class="code">end</code></pre></body></html>
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