--- AnyEvent-MP/MP.pm 2009/08/28 01:07:24 1.66 +++ AnyEvent-MP/MP.pm 2009/08/28 22:21:53 1.67 @@ -42,8 +42,10 @@ AnyEvent::MP - stable API, should work AnyEvent::MP::Intro - outdated - AnyEvent::MP::Kernel - WIP - AnyEvent::MP::Transport - mostly stable + AnyEvent::MP::Kernel - mostly stable + AnyEvent::MP::Global - mostly stable + AnyEvent::MP::Node - mostly stable, but internal anyways + AnyEvent::MP::Transport - mostly stable, but internal anyways stay tuned. @@ -52,14 +54,12 @@ This module (-family) implements a simple message passing framework. Despite its simplicity, you can securely message other processes running -on the same or other hosts. +on the same or other hosts, and you can supervise entities remotely. For an introduction to this module family, see the L -manual page. +manual page and the examples under F. -At the moment, this module family is severly broken and underdocumented, -so do not use. This was uploaded mainly to reserve the CPAN namespace - -stay tuned! +At the moment, this module family is a bit underdocumented. =head1 CONCEPTS @@ -73,22 +73,20 @@ some messages. Messages send to ports will not be queued, regardless of anything was listening for them or not. -=item port ID - C +=item port ID - C -A port ID is the concatenation of a noderef, a hash-mark (C<#>) as -separator, and a port name (a printable string of unspecified format). An -exception is the the node port, whose ID is identical to its node -reference. +A port ID is the concatenation of a node ID, a hash-mark (C<#>) as +separator, and a port name (a printable string of unspecified format). =item node A node is a single process containing at least one port - the node port, -which provides nodes to manage each other remotely, and to create new +which enables nodes to manage each other remotely, and to create new ports. -Nodes are either private (single-process only), slaves (can only talk to -public nodes, but do not need an open port) or public nodes (connectable -from any other node). +Nodes are either public (have one or more listening ports) or private +(no listening ports). Private nodes cannot talk to other private nodes +currently. =item node ID - C<[a-za-Z0-9_\-.:]+> @@ -116,6 +114,9 @@ error), they try to re-establish connections to some seednodes again to join the network. +Apart from being sued for seeding, seednodes are not special in any way - +every public node can be a seednode. + =back =head1 VARIABLES/FUNCTIONS @@ -140,7 +141,7 @@ our @EXPORT = qw( NODE $NODE *SELF node_of after - resolve_node initialise_node + initialise_node snd rcv mon mon_guard kil reg psub spawn port ); @@ -155,13 +156,13 @@ =item $thisnode = NODE / $NODE -The C function returns, and the C<$NODE> variable contains the node +The C function returns, and the C<$NODE> variable contains, the node ID of the node running in the current process. This value is initialised by a call to C. =item $nodeid = node_of $port -Extracts and returns the node ID part from a port ID or a node ID. +Extracts and returns the node ID from a port ID or a node ID. =item initialise_node $profile_name @@ -219,32 +220,37 @@ Contains the current port id while executing C callbacks or C blocks. -=item SELF, %SELF, @SELF... +=item *SELF, SELF, %SELF, @SELF... Due to some quirks in how perl exports variables, it is impossible to -just export C<$SELF>, all the symbols called C are exported by this +just export C<$SELF>, all the symbols named C are exported by this module, but only C<$SELF> is currently used. =item snd $port, type => @data =item snd $port, @msg -Send the given message to the given port ID, which can identify either -a local or a remote port, and must be a port ID. +Send the given message to the given port, which can identify either a +local or a remote port, and must be a port ID. -While the message can be about anything, it is highly recommended to use a -string as first element (a port ID, or some word that indicates a request -type etc.). - -The message data effectively becomes read-only after a call to this -function: modifying any argument is not allowed and can cause many -problems. +While the message can be almost anything, it is highly recommended to +use a string as first element (a port ID, or some word that indicates a +request type etc.) and to consist if only simple perl values (scalars, +arrays, hashes) - if you think you need to pass an object, think again. + +The message data logically becomes read-only after a call to this +function: modifying any argument (or values referenced by them) is +forbidden, as there can be considerable time between the call to C +and the time the message is actually being serialised - in fact, it might +never be copied as within the same process it is simply handed to the +receiving port. The type of data you can transfer depends on the transport protocol: when JSON is used, then only strings, numbers and arrays and hashes consisting of those are allowed (no objects). When Storable is used, then anything that Storable can serialise and deserialise is allowed, and for the local -node, anything can be passed. +node, anything can be passed. Best rely only on the common denominator of +these. =item $local_port = port @@ -430,28 +436,28 @@ } } -=item $guard = mon $port, $cb->(@reason) +=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies -=item $guard = mon $port, $rcvport +=item $guard = mon $port, $rcvport # kill $rcvport when $port dies -=item $guard = mon $port +=item $guard = mon $port # kill $SELF when $port dies -=item $guard = mon $port, $rcvport, @msg +=item $guard = mon $port, $rcvport, @msg # send a message when $port dies Monitor the given port and do something when the port is killed or messages to it were lost, and optionally return a guard that can be used to stop monitoring again. C effectively guarantees that, in the absence of hardware failures, -that after starting the monitor, either all messages sent to the port -will arrive, or the monitoring action will be invoked after possible -message loss has been detected. No messages will be lost "in between" -(after the first lost message no further messages will be received by the +after starting the monitor, either all messages sent to the port will +arrive, or the monitoring action will be invoked after possible message +loss has been detected. No messages will be lost "in between" (after +the first lost message no further messages will be received by the port). After the monitoring action was invoked, further messages might get delivered again. -Note that monitoring-actions are one-shot: once released, they are removed -and will not trigger again. +Note that monitoring-actions are one-shot: once messages are lost (and a +monitoring alert was raised), they are removed and will not trigger again. In the first form (callback), the callback is simply called with any number of C<@reason> elements (no @reason means that the port was deleted @@ -523,10 +529,10 @@ Optionally returns a guard that will stop the monitoring. This function is useful when you create e.g. timers or other watchers and -want to free them when the port gets killed: +want to free them when the port gets killed (note the use of C): $port->rcv (start => sub { - my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub { + my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub { undef $timer if 0.9 < rand; }); }); @@ -545,11 +551,12 @@ Kill the specified port with the given C<@reason>. -If no C<@reason> is specified, then the port is killed "normally" (linked -ports will not be kileld, or even notified). +If no C<@reason> is specified, then the port is killed "normally" (ports +monitoring other ports will not necessarily die because a port dies +"normally"). Otherwise, linked ports get killed with the same reason (second form of -C, see below). +C, see above). Runtime errors while evaluating C callbacks or inside C blocks will be reported as reason C<< die => $@ >>. @@ -564,13 +571,13 @@ Creates a port on the node C<$node> (which can also be a port ID, in which case it's the node where that port resides). -The port ID of the newly created port is return immediately, and it is -permissible to immediately start sending messages or monitor the port. +The port ID of the newly created port is returned immediately, and it is +possible to immediately start sending messages or to monitor the port. -After the port has been created, the init function is -called. This function must be a fully-qualified function name -(e.g. C). To specify a function in the main -program, use C<::name>. +After the port has been created, the init function is called on the remote +node, in the same context as a C callback. This function must be a +fully-qualified function name (e.g. C). To +specify a function in the main program, use C<::name>. If the function doesn't exist, then the node tries to C the package, then the package above the package and so on (e.g. @@ -580,9 +587,10 @@ The init function is then called with the newly-created port as context object (C<$SELF>) and the C<@initdata> values as arguments. -A common idiom is to pass your own port, monitor the spawned port, and -in the init function, monitor the original port. This two-way monitoring -ensures that both ports get cleaned up when there is a problem. +A common idiom is to pass a local port, immediately monitor the spawned +port, and in the remote init function, immediately monitor the passed +local port. This two-way monitoring ensures that both ports get cleaned up +when there is a problem. Example: spawn a chat server port on C<$othernode>. @@ -634,7 +642,9 @@ Either sends the given message, or call the given callback, after the specified number of seconds. -This is simply a utility function that come sin handy at times. +This is simply a utility function that comes in handy at times - the +AnyEvent::MP author is not convinced of the wisdom of having it, though, +so it may go away in the future. =cut @@ -735,7 +745,8 @@ The AEMP protocol, unlike the Erlang protocol, supports both programming language independent text-only protocols (good for debugging) and binary, -language-specific serialisers (e.g. Storable). +language-specific serialisers (e.g. Storable). By default, unless TLS is +used, the protocol is actually completely text-based. It has also been carefully designed to be implementable in other languages with a minimum of work while gracefully degrading functionality to make the @@ -751,14 +762,14 @@ =item * Erlang tries to hide remote/local connections, AEMP does not. -Monitoring in Erlang is not an indicator of process death/crashes, -as linking is (except linking is unreliable in Erlang). +Monitoring in Erlang is not an indicator of process death/crashes, in the +same way as linking is (except linking is unreliable in Erlang). In AEMP, you don't "look up" registered port names or send to named ports that might or might not be persistent. Instead, you normally spawn a port -on the remote node. The init function monitors the you, and you monitor -the remote port. Since both monitors are local to the node, they are much -more reliable. +on the remote node. The init function monitors you, and you monitor the +remote port. Since both monitors are local to the node, they are much more +reliable (no need for C). This also saves round-trips and avoids sending messages to the wrong port (hard to do in Erlang). @@ -769,29 +780,29 @@ =over 4 -=item Why strings for ports and noderefs, why not objects? +=item Why strings for port and node IDs, why not objects? We considered "objects", but found that the actual number of methods -thatc an be called are very low. Since port IDs and noderefs travel over +that can be called are quite low. Since port and node IDs travel over the network frequently, the serialising/deserialising would add lots of -overhead, as well as having to keep a proxy object. +overhead, as well as having to keep a proxy object everywhere. Strings can easily be printed, easily serialised etc. and need no special procedures to be "valid". -And a a miniport consists of a single closure stored in a global hash - it -can't become much cheaper. +And as a result, a miniport consists of a single closure stored in a +global hash - it can't become much cheaper. -=item Why favour JSON, why not real serialising format such as Storable? +=item Why favour JSON, why not a real serialising format such as Storable? In fact, any AnyEvent::MP node will happily accept Storable as framing format, but currently there is no way to make a node use Storable by -default. +default (although all nodes will accept it). The default framing protocol is JSON because a) JSON::XS is many times faster for small messages and b) most importantly, after years of experience we found that object serialisation is causing more problems -than it gains: Just like function calls, objects simply do not travel +than it solves: Just like function calls, objects simply do not travel easily over the network, mostly because they will always be a copy, so you always have to re-think your design.