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 tem-
porarily 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(
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 infor-
mation 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.