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Tcl_CreateFileHandler(3) Tcl Library Procedures Tcl_CreateFileHandler(3)
Tcl_CreateFileHandler, Tcl_DeleteFileHandler - associate procedure
callbacks with files or devices (Unix only)
Tcl_CreateFileHandler(fd, mask, proc, clientData)
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
ClientData clientData (in) Arbitrary one-word value to pass
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(
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
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
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
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(n), Tcl_CreateTimerHandler(3), Tcl_DoWhenIdle(3)
callback, file, handler
Tcl 8.0 Tcl_CreateFileHandler(3)