Tcl_CreateFileHandler, Tcl_DeleteFileHandler - associate procedure callbacks
with files or devices (Unix only)
#include <tcl.h>
Tcl_CreateFileHandler(fd, mask, proc, clientData)
Tcl_DeleteFileHandler(fd)
- 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.
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.
fileevent(3tcl),
Tcl_CreateTimerHandler(3tcl),
Tcl_DoWhenIdle(3tcl)
callback, file, handler