xpamainloop(3) [debian man page]
xpamainloop(3) SAORD Documentation xpamainloop(3) NAME
XPAMainLoop - optional main loop for XPA SYNOPSIS
#include <xpa.h> void XPAMainLoop(); DESCRIPTION
Once XPA access points have been defined, a program must enter an event loop to watch for requests from external programs. This can be done in a variety of ways, depending on whether the event loop is processing events other than XPA events. In cases where there are no non-XPA events to be processed, the program can simply call the XPAMainLoop() event loop. This loop is implemented essentially as follows (error checking is simplified in this example): FD_ZERO(&readfds); while( XPAAddSelect(NULL, &readfds) ){ if( sgot = select(swidth, &readfds, NULL, NULL, NULL) >0 ) XPAProcessSelect(&readfds, 0); else break; FD_ZERO(&readfds); } The XPAAddSelect() routine sets up the select() readfds variable so that select() will wait for I/O on all the active XPA channels. It returns the number of XPAs that are active; the loop will end when there are no active XPAs. The standard select() routine is called to wait for an external I/O request. Since no timeout struct is passed in argument 5, the select() call hangs until there is an external request. When an external I/O request is made, the XPAProcessSelect() routine is executed to process the pending requests. In this rou- tine, the maxreq value determines how many requests will be processed: if maxreq <=0, then all currently pending requests will be pro- cessed. Otherwise, up to maxreq requests will be processed. (The most usual values for maxreq is 0 to process all requests.) If a program has its own Unix select() loop, then XPA access points can be added to it by using a variation of the standard XPAMainLoop: XPAAddSelect(xpa, &readfds); [app-specific ...] if( select(width, &readfds, ...) ){ XPAProcessSelect(&readfds, maxreq); [app-specific ...] FD_ZERO(&readfds); } XPAAddSelect() is called before select() to add the access points. If the first argument is NULL, then all active XPA access points are added. Otherwise only the specified access point is added. After select() is called, the XPAProcessSelect() routine can be called to process XPA requests. Once again, the maxreq value determines how many requests will be processed: if maxreq <=0, then all currently pend- ing requests will be processed. Otherwise, up to maxreq requests will be processed. XPA access points can be added to Xt event loops (using XtAppMainLoop()) and Tcl/Tk event loops (using vwait and the Tk loop). When using XPA with these event loops, you only need to call: int XPAXtAddInput(XtAppContext app, XPA xpa) or int XPATclAddInput(XPA xpa) respectively before entering the loop. SEE ALSO
See xpa(7) for a list of XPA help pages version 2.1.14 June 7, 2012 xpamainloop(3)
Check Out this Related Man Page
xpaintro(7) SAORD Documentation xpaintro(7) NAME
XPAIntro - Introduction to the XPA Messaging System SYNOPSIS
A brief introduction to the XPA messaging system, which provides seamless communication between all kinds of Unix event-driven programs, including X programs, Tcl/Tk programs, and Perl programs. DESCRIPTION
The XPA messaging system provides seamless communication between all kinds of Unix programs, including X programs, Tcl/Tk programs, and Perl programs. It also provides an easy way for users to communicate with these XPA-enabled programs by executing XPA client commands in the shell or by utilizing such commands in scripts. Because XPA works both at the programming level and the shell level, it is a powerful tool for unifying any analysis environment: users and programmers have great flexibility in choosing the best level or levels at which to access XPA services, and client access can be extended or modified easily at any time. A program becomes an XPA-enabled server by defining named points of public access through which data and commands can be exchanged with other client programs (and users). Using standard TCP sockets as a transport mechanism, XPA supports both single-point and broadcast mes- saging to and from these servers. It supports direct communication between clients and servers, or indirect communication via an interme- diate message bus emulation program. Host-based access control is implemented, as is as the ability to communicate with XPA servers across a network. XPA implements a layered interface that is designed to be useful both to software developers and to users. The interface consists of a library of XPA client and server routines for use in programs and a suite of high-level user programs built on top of these libraries. Using the XPA library, access points can be added to Tcl/Tk programs, Xt programs, or to Unix programs that use the XPA event loop or any event loop based on select(). Client access subroutines can be added to any Tcl/Tk or Unix program. Client access also is supported at the command line via a suite of high-level programs. The major components of the XPA layered interface are: o A set of XPA server routines, centered on XPANew(), which are used by XPA server programs to tag public access points with string iden- tifiers and to register send and receive callbacks for these access points. o A set of XPA client routines, centered on the XPASet() and XPAGet(), which are used by external client applications to exchange data and commands with an XPA server. o High-level programs, centered on xpaset and xpaget, which allow data and information to be exchanged with XPA server programs from the command line and from scripts. These programs have the command syntax: [data] | xpaset [qualifiers ...] xpaget [qualifiers ...] o An XPA name server program, xpans, through which XPA access point names are registered by servers and distributed to clients. Defining an XPA access point is easy: a server application calls XPANew(), XPACmdNew(), or the experimental XPAInfoNew() routine to create a named public access point. An XPA service can specify "send" and "receive" callback procedures (or an "info" procedure in the case of XPAInfoNew()) to be executed by the program when an external process either sends data or commands to this access point or requests data or information from this access point. Either of the callbacks can be omitted, so that a particular access point can be specified as read-only, read-write, or write-only. Application-specific client data can be associated with these callbacks. Having defined one or more public access points in this way, an XPA server program enters its usual event loop (or uses the standard XPA event loop). Clients communicate with these XPA public access points using programs such as xpaget, xpaset, and xpainfo (at the command line), or rou- tines such as XPAGet(), XPASet(), and XPAInfo() within a program. Both methods require specification of the name of the access point. The xpaget program returns data or other information from an XPA server to its standard output, while the xpaset program sends data or commands from its standard input to an XPA application. The corresponding API routines set/get data to/from memory, returning error messages and other info as needed. If a template is used to specify the access point name (e.g., "ds9*"), then communication will take place with all servers matching that template. Please note that XPA currently is not thread-safe. All XPA calls must be in the same thread. SEE ALSO
See xpa(7) for a list of XPA help pages version 2.1.14 June 7, 2012 xpaintro(7)