15b6757b26
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@51901 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
225 lines
8.9 KiB
C++
225 lines
8.9 KiB
C++
/////////////////////////////////////////////////////////////////////////////
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// Name: ipc
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// Purpose: topic overview
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// Author: wxWidgets team
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// RCS-ID: $Id$
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// Licence: wxWindows license
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/////////////////////////////////////////////////////////////////////////////
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/*!
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@page ipc_overview Interprocess communication overview
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Classes: #wxServer,
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#wxConnection,
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#wxClient
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wxWidgets has a number of different classes to help with
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interprocess communication and network programming. This section
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only discusses one family of classes -- the DDE-like protocol --
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but here's a list of other useful classes:
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#wxSocketEvent,
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#wxSocketBase,
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#wxSocketClient,
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#wxSocketServer: classes for the low-level TCP/IP API.
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#wxProtocol, #wxURL, #wxFTP, #wxHTTP: classes
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for programming popular Internet protocols.
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wxWidgets' DDE-like protocol is a high-level protocol based on
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Windows DDE. There are two implementations of this DDE-like
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protocol: one using real DDE running on Windows only, and another
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using TCP/IP (sockets) that runs on most platforms. Since the API
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and virtually all of the behaviour is the same apart from the
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names of the classes, you should find it easy to switch between
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the two implementations.
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Notice that by including @c wx/ipc.h you may define
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convenient synonyms for the IPC classes: @c wxServer for either
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@c wxDDEServer or @c wxTCPServer depending on whether
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DDE-based or socket-based implementation is used and the same
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thing for @c wxClient and @c wxConnection.
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By default, the DDE implementation is used under Windows. DDE works
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within one computer only. If you want to use IPC between
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different workstations you should define @c wxUSE_DDE_FOR_IPC as 0 before including this header -- this
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will force using TCP/IP implementation even under Windows.
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The following description refers to wx... but remember that the
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equivalent wxTCP... and wxDDE... classes can be used in much the
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same way.
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Three classes are central to the DDE-like API:
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wxClient. This represents the client application, and is used
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only within a client program.
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wxServer. This represents the server application, and is used
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only within a server program.
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wxConnection. This represents the connection from the
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client to the server - both the client and the server use an
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instance of this class, one per connection. Most DDE transactions
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operate on this object.
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Messages between applications are usually identified by three
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variables: connection object, topic name and item name. A data
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string is a fourth element of some messages. To create a
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connection (a conversation in Windows parlance), the client
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application uses wxClient::MakeConnection to send a message to the
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server object, with a string service name to identify the server
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and a topic name to identify the topic for the duration of the
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connection. Under Unix, the service name may be either an integer
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port identifier in which case an Internet domain socket will be
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used for the communications or a valid file name (which shouldn't
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exist and will be deleted afterwards) in which case a Unix domain
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socket is created.
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@b SECURITY NOTE: Using Internet domain sockets is extremely insecure for
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IPC as there is absolutely no access control for them, use Unix domain sockets
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whenever possible!
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The server then responds and either vetoes the connection or
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allows it. If allowed, both the server and client objects create
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wxConnection objects which persist until the connection is
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closed. The connection object is then used for sending and
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receiving subsequent messages between client and server -
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overriding virtual functions in your class derived from
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wxConnection allows you to handle the DDE messages.
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To create a working server, the programmer must:
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Derive a class from wxConnection, providing handlers for various messages sent to the server
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side of a wxConnection (e.g. OnExecute, OnRequest, OnPoke). Only
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the handlers actually required by the application need to be
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overridden.
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Derive a class from wxServer, overriding OnAcceptConnection
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to accept or reject a connection on the basis of the topic
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argument. This member must create and return an instance of the
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derived connection class if the connection is accepted.
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Create an instance of your server object and call Create to
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activate it, giving it a service name.
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To create a working client, the programmer must:
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Derive a class from wxConnection, providing handlers for various
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messages sent to the client side of a wxConnection (e.g.
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OnAdvise). Only the handlers actually required by the application
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need to be overridden.
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Derive a class from wxClient, overriding OnMakeConnection to
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create and return an instance of the derived connection class.
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Create an instance of your client object.
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When appropriate, create a new connection using
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wxClient::MakeConnection,
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with arguments host name (processed in Unix only, use 'localhost'
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for local computer), service name, and topic name for this
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connection. The client object will call
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#OnMakeConnection to create
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a connection object of the derived class if the connection is
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successful.
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Use the wxConnection member functions to send messages to the server.
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@ref datatransfer_overview
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#Examples
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@ref ddedetails_overview
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@section datatransfer Data transfer
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These are the ways that data can be transferred from one
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application to another. These are methods of wxConnection.
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@b Execute: the client calls the server with a data string representing
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a command to be executed. This succeeds or fails, depending on the
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server's willingness to answer. If the client wants to find the result
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of the Execute command other than success or failure, it has to explicitly
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call Request.
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@b Request: the client asks the server for a particular data string
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associated with a given item string. If the server is unwilling to
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reply, the return value is @NULL. Otherwise, the return value is a string
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(actually a pointer to the connection buffer, so it should not be
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deallocated by the application).
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@b Poke: The client sends a data string associated with an item
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string directly to the server. This succeeds or fails.
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@b Advise: The client asks to be advised of any change in data
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associated with a particular item. If the server agrees, the server will
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send an OnAdvise message to the client along with the item and data.
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The default data type is wxCF_TEXT (ASCII text), and the default data
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size is the length of the null-terminated string. Windows-specific data
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types could also be used on the PC.
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@section ipcexamples Examples
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See the sample programs @e server and @e client in the IPC
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samples directory. Run the server, then the client. This demonstrates
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using the Execute, Request, and Poke commands from the client, together
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with an Advise loop: selecting an item in the server list box causes
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that item to be highlighted in the client list box.
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@section ddedetails More DDE details
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A wxClient object initiates the client part of a client-server
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DDE-like (Dynamic Data Exchange) conversation (available in both
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Windows and Unix).
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To create a client which can communicate with a suitable server,
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you need to derive a class from wxConnection and another from
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wxClient. The custom wxConnection class will receive
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communications in a 'conversation' with a server. and the custom
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wxServer is required so that a user-overridden
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wxClient::OnMakeConnection
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member can return a wxConnection of the required class, when a
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connection is made.
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For example:
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@code
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class MyConnection: public wxConnection {
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public:
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MyConnection(void)::wxConnection() {}
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~MyConnection(void) { }
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bool OnAdvise(const wxString& topic, const wxString& item, char *data, int size, wxIPCFormat format)
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{ wxMessageBox(topic, data); }
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};
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class MyClient: public wxClient {
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public:
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MyClient(void) {}
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wxConnectionBase *OnMakeConnection(void) { return new MyConnection; }
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};
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@endcode
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Here, @b MyConnection will respond to
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#OnAdvise messages sent by the
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server by displaying a message box.
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When the client application starts, it must create an instance of
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the derived wxClient. In the following, command line arguments
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are used to pass the host name (the name of the machine the
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server is running on) and the server name (identifying the server
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process). Calling
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wxClient::MakeConnection
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implicitly creates an instance of @b MyConnection if the
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request for a connection is accepted, and the client then
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requests an @e Advise loop from the server (an Advise loop is
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where the server calls the client when data has changed).
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@code
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wxString server = "4242";
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wxString hostName;
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wxGetHostName(hostName);
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// Create a new client
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MyClient *client = new MyClient;
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connection = (MyConnection *)client-MakeConnection(hostName, server, "IPC TEST");
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if (!connection)
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{
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wxMessageBox("Failed to make connection to server", "Client Demo Error");
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return @NULL;
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}
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connection-StartAdvise("Item");
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@endcode
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*/
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