Tcl_CreateFileHandler(3) Tcl Library Procedures Tcl_CreateFileHandler(3)

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NAME

Tcl_CreateFileHandler, Tcl_DeleteFileHandler - associate procedure
callbacks with files or devices (Unix only)

SYNOPSIS

#include <tcl.h>

Tcl_CreateFileHandler(fd, mask, proc, clientData)

Tcl_DeleteFileHandler(fd)

ARGUMENTS

int fd (in) Unix file descriptor for an
open file or device.

int mask (in) Conditions under which proc
should be called: OR-ed
combination of TCL_READABLE,
TCL_WRITABLE, and
TCL_EXCEPTION. May be set to 0
to temporarily disable a
handler.

Tcl_FileProc *proc (in) Procedure to invoke whenever
the file or device indicated by
file meets the conditions
specified by mask.

ClientData clientData (in) Arbitrary one-word value to
pass to proc.
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DESCRIPTION

Tcl_CreateFileHandler arranges for proc to be invoked in the future
whenever I/O becomes possible on a file or an exceptional condition
exists for the file. The file is indicated by fd, and the conditions
of interest are indicated by mask. For example, if mask is
TCL_READABLE, proc will be called when the file is readable. The
callback to proc is made by Tcl_DoOneEvent, so Tcl_CreateFileHandler
is only useful in programs that dispatch events through
Tcl_DoOneEvent or through Tcl commands such as vwait.

Proc should have arguments and result that match the type
Tcl_FileProc:

typedef void Tcl_FileProc(
ClientData clientData,
int mask);

The clientData parameter to proc is a copy of the clientData argument
given to Tcl_CreateFileHandler when the callback was created.
Typically, clientData points to a data structure containing
application-specific information about the file. Mask is an integer
mask indicating which of the requested conditions actually exists for
the file; it will contain a subset of the bits in the mask argument
to Tcl_CreateFileHandler.

There may exist only one handler for a given file at a given time.
If Tcl_CreateFileHandler is called when a handler already exists for
fd, then the new callback replaces the information that was
previously recorded.

Tcl_DeleteFileHandler may be called to delete the file handler for
fd; if no handler exists for the file given by fd then the procedure
has no effect.

The purpose of file handlers is to enable an application to respond
to events while waiting for files to become ready for I/O. For this
to work correctly, the application may need to use non-blocking I/O
operations on the files for which handlers are declared. Otherwise
the application may block if it reads or writes too much data; while
waiting for the I/O to complete the application will not be able to
service other events. Use Tcl_SetChannelOption with -blocking to set
the channel into blocking or nonblocking mode as required.

Note that these interfaces are only supported by the Unix
implementation of the Tcl notifier.

SEE ALSO

fileevent(n), Tcl_CreateTimerHandler(3), Tcl_DoWhenIdle(3)

KEYWORDS

callback, file, handler

Tcl 8.0 Tcl_CreateFileHandler(3)