Tcl_CreateChannel

Tcl_CreateChannel(3)        Tcl Library Procedures        Tcl_CreateChannel(3)



______________________________________________________________________________

NAME
       Tcl_CreateChannel, Tcl_GetChannelInstanceData, Tcl_GetChannelType,
       Tcl_GetChannelName, Tcl_GetChannelHandle, Tcl_GetChannelMode,
       Tcl_GetChannelBufferSize, Tcl_SetChannelBufferSize, Tcl_NotifyChannel,
       Tcl_BadChannelOption, Tcl_ChannelName, Tcl_ChannelVersion,
       Tcl_ChannelBlockModeProc, Tcl_ChannelCloseProc, Tcl_ChannelClose2Proc,
       Tcl_ChannelInputProc, Tcl_ChannelOutputProc, Tcl_ChannelSeekProc,
       Tcl_ChannelWideSeekProc, Tcl_ChannelTruncateProc,
       Tcl_ChannelSetOptionProc, Tcl_ChannelGetOptionProc,
       Tcl_ChannelWatchProc, Tcl_ChannelGetHandleProc, Tcl_ChannelFlushProc,
       Tcl_ChannelHandlerProc, Tcl_ChannelThreadActionProc,
       Tcl_IsChannelShared, Tcl_IsChannelRegistered, Tcl_CutChannel,
       Tcl_SpliceChannel, Tcl_IsChannelExisting, Tcl_ClearChannelHandlers,
       Tcl_GetChannelThread, Tcl_ChannelBuffered - procedures for creating and
       manipulating channels

SYNOPSIS
       #include <tcl.h>

       Tcl_Channel
       Tcl_CreateChannel(typePtr, channelName, instanceData, mask)

       ClientData
       Tcl_GetChannelInstanceData(channel)

       const Tcl_ChannelType *
       Tcl_GetChannelType(channel)

       const char *
       Tcl_GetChannelName(channel)

       int
       Tcl_GetChannelHandle(channel, direction, handlePtr)

       Tcl_ThreadId
       Tcl_GetChannelThread(channel)

       int
       Tcl_GetChannelMode(channel)

       int
       Tcl_GetChannelBufferSize(channel)

       Tcl_SetChannelBufferSize(channel, size)

       Tcl_NotifyChannel(channel, mask)

       int
       Tcl_BadChannelOption(interp, optionName, optionList)

       int
       Tcl_IsChannelShared(channel)

       int
       Tcl_IsChannelRegistered(interp, channel)

       int
       Tcl_IsChannelExisting(channelName)

       void
       Tcl_CutChannel(channel)

       void
       Tcl_SpliceChannel(channel)

       void
       Tcl_ClearChannelHandlers(channel)

       int
       Tcl_ChannelBuffered(channel)

       const char *
       Tcl_ChannelName(typePtr)

       Tcl_ChannelTypeVersion
       Tcl_ChannelVersion(typePtr)

       Tcl_DriverBlockModeProc *
       Tcl_ChannelBlockModeProc(typePtr)

       Tcl_DriverCloseProc *
       Tcl_ChannelCloseProc(typePtr)

       Tcl_DriverClose2Proc *
       Tcl_ChannelClose2Proc(typePtr)

       Tcl_DriverInputProc *
       Tcl_ChannelInputProc(typePtr)

       Tcl_DriverOutputProc *
       Tcl_ChannelOutputProc(typePtr)

       Tcl_DriverSeekProc *
       Tcl_ChannelSeekProc(typePtr)

       Tcl_DriverWideSeekProc *
       Tcl_ChannelWideSeekProc(typePtr)

       Tcl_DriverThreadActionProc *
       Tcl_ChannelThreadActionProc(typePtr)

       Tcl_DriverTruncateProc *
       Tcl_ChannelTruncateProc(typePtr)

       Tcl_DriverSetOptionProc *
       Tcl_ChannelSetOptionProc(typePtr)

       Tcl_DriverGetOptionProc *
       Tcl_ChannelGetOptionProc(typePtr)

       Tcl_DriverWatchProc *
       Tcl_ChannelWatchProc(typePtr)

       Tcl_DriverGetHandleProc *
       Tcl_ChannelGetHandleProc(typePtr)

       Tcl_DriverFlushProc *
       Tcl_ChannelFlushProc(typePtr)

       Tcl_DriverHandlerProc *
       Tcl_ChannelHandlerProc(typePtr)


ARGUMENTS
       const Tcl_ChannelType *typePtr (in)              Points to a structure
                                                        containing the
                                                        addresses of
                                                        procedures that can be
                                                        called to perform I/O
                                                        and other functions on
                                                        the channel.

       const char *channelName (in)                     The name of this
                                                        channel, such as
                                                        file3; must not be in
                                                        use by any other
                                                        channel. Can be NULL,
                                                        in which case the
                                                        channel is created
                                                        without a name. If the
                                                        created channel is
                                                        assigned to one of the
                                                        standard channels
                                                        (stdin, stdout or
                                                        stderr), the assigned
                                                        channel name will be
                                                        the name of the
                                                        standard channel.

       ClientData instanceData (in)                     Arbitrary one-word
                                                        value to be associated
                                                        with this channel.
                                                        This value is passed
                                                        to procedures in
                                                        typePtr when they are
                                                        invoked.

       int mask (in)                                    OR-ed combination of
                                                        TCL_READABLE and
                                                        TCL_WRITABLE to
                                                        indicate whether a
                                                        channel is readable
                                                        and writable.

       Tcl_Channel channel (in)                         The channel to operate
                                                        on.

       int direction (in)                               TCL_READABLE means the
                                                        input handle is
                                                        wanted; TCL_WRITABLE
                                                        means the output
                                                        handle is wanted.

       ClientData *handlePtr (out)                      Points to the location
                                                        where the desired OS-
                                                        specific handle should
                                                        be stored.

       int size (in)                                    The size, in bytes, of
                                                        buffers to allocate in
                                                        this channel.

       int mask (in)                                    An OR-ed combination
                                                        of TCL_READABLE,
                                                        TCL_WRITABLE and
                                                        TCL_EXCEPTION that
                                                        indicates events that
                                                        have occurred on this
                                                        channel.

       Tcl_Interp *interp (in)                          Current interpreter.
                                                        (can be NULL)

       const char *optionName (in)                      Name of the invalid
                                                        option.

       const char *optionList (in)                      Specific options list
                                                        (space separated
                                                        words, without “-”) to
                                                        append to the standard
                                                        generic options list.
                                                        Can be NULL for
                                                        generic options error
                                                        message only.
______________________________________________________________________________

DESCRIPTION
       Tcl uses a two-layered channel architecture. It provides a generic
       upper layer to enable C and Tcl programs to perform input and output
       using the same APIs for a variety of files, devices, sockets etc. The
       generic C APIs are described in the manual entry for
       Tcl_OpenFileChannel.

       The lower layer provides type-specific channel drivers for each type of
       device supported on each platform.  This manual entry describes the C
       APIs used to communicate between the generic layer and the type-
       specific channel drivers.  It also explains how new types of channels
       can be added by providing new channel drivers.

       Channel drivers consist of a number of components: First, each channel
       driver provides a Tcl_ChannelType structure containing pointers to
       functions implementing the various operations used by the generic layer
       to communicate with the channel driver. The Tcl_ChannelType structure
       and the functions referenced by it are described in the section
       TCL_CHANNELTYPE, below.

       Second, channel drivers usually provide a Tcl command to create
       instances of that type of channel. For example, the Tcl open command
       creates channels that use the file and command channel drivers, and the
       Tcl socket command creates channels that use TCP sockets for network
       communication.

       Third, a channel driver optionally provides a C function to open
       channel instances of that type. For example, Tcl_OpenFileChannel opens
       a channel that uses the file channel driver, and Tcl_OpenTcpClient
       opens a channel that uses the TCP network protocol.  These creation
       functions typically use Tcl_CreateChannel internally to open the
       channel.

       To add a new type of channel you must implement a C API or a Tcl
       command that opens a channel by invoking Tcl_CreateChannel.  When your
       driver calls Tcl_CreateChannel it passes in a Tcl_ChannelType structure
       describing the driver's I/O procedures.  The generic layer will then
       invoke the functions referenced in that structure to perform operations
       on the channel.

       Tcl_CreateChannel opens a new channel and associates the supplied
       typePtr and instanceData with it. The channel is opened in the mode
       indicated by mask.  For a discussion of channel drivers, their
       operations and the Tcl_ChannelType structure, see the section
       TCL_CHANNELTYPE, below.

       Tcl_CreateChannel interacts with the code managing the standard
       channels. Once a standard channel was initialized either through a call
       to Tcl_GetStdChannel or a call to Tcl_SetStdChannel closing this
       standard channel will cause the next call to Tcl_CreateChannel to make
       the new channel the new standard channel too. See Tcl_StandardChannels
       for a general treatise about standard channels and the behavior of the
       Tcl library with regard to them.

       Tcl_GetChannelInstanceData returns the instance data associated with
       the channel in channel. This is the same as the instanceData argument
       in the call to Tcl_CreateChannel that created this channel.

       Tcl_GetChannelType returns a pointer to the Tcl_ChannelType structure
       used by the channel in the channel argument. This is the same as the
       typePtr argument in the call to Tcl_CreateChannel that created this
       channel.

       Tcl_GetChannelName returns a string containing the name associated with
       the channel, or NULL if the channelName argument to Tcl_CreateChannel
       was NULL.

       Tcl_GetChannelHandle places the OS-specific device handle associated
       with channel for the given direction in the location specified by
       handlePtr and returns TCL_OK.  If the channel does not have a device
       handle for the specified direction, then TCL_ERROR is returned instead.
       Different channel drivers will return different types of handle.  Refer
       to the manual entries for each driver to determine what type of handle
       is returned.

       Tcl_GetChannelThread returns the id of the thread currently managing
       the specified channel. This allows channel drivers to send their file
       events to the correct event queue even for a multi-threaded core.

       Tcl_GetChannelMode returns an OR-ed combination of TCL_READABLE and
       TCL_WRITABLE, indicating whether the channel is open for input and
       output.

       Tcl_GetChannelBufferSize returns the size, in bytes, of buffers
       allocated to store input or output in channel. If the value was not set
       by a previous call to Tcl_SetChannelBufferSize, described below, then
       the default value of 4096 is returned.

       Tcl_SetChannelBufferSize sets the size, in bytes, of buffers that will
       be allocated in subsequent operations on the channel to store input or
       output. The size argument should be between one and one million,
       allowing buffers of one byte to one million bytes. If size is outside
       this range, Tcl_SetChannelBufferSize sets the buffer size to 4096.

       Tcl_NotifyChannel is called by a channel driver to indicate to the
       generic layer that the events specified by mask have occurred on the
       channel.  Channel drivers are responsible for invoking this function
       whenever the channel handlers need to be called for the channel.  See
       WATCHPROC below for more details.

       Tcl_BadChannelOption is called from driver specific setOptionProc or
       getOptionProc to generate a complete error message.

       Tcl_ChannelBuffered returns the number of bytes of input currently
       buffered in the internal buffer (push back area) of the channel itself.
       It does not report about the data in the overall buffers for the stack
       of channels the supplied channel is part of.

       Tcl_IsChannelShared checks the refcount of the specified channel and
       returns whether the channel was shared among multiple interpreters
       (result == 1) or not (result == 0).

       Tcl_IsChannelRegistered checks whether the specified channel is
       registered in the given interpreter (result == 1) or not (result == 0).

       Tcl_IsChannelExisting checks whether a channel with the specified name
       is registered in the (thread)-global list of all channels (result == 1)
       or not (result == 0).

       Tcl_CutChannel removes the specified channel from the (thread)global
       list of all channels (of the current thread).  Application to a channel
       still registered in some interpreter is not allowed.  Also notifies the
       driver if the Tcl_ChannelType version is TCL_CHANNEL_VERSION_4 (or
       higher), and Tcl_DriverThreadActionProc is defined for it.

       Tcl_SpliceChannel adds the specified channel to the (thread)global list
       of all channels (of the current thread).  Application to a channel
       registered in some interpreter is not allowed.  Also notifies the
       driver if the Tcl_ChannelType version is TCL_CHANNEL_VERSION_4 (or
       higher), and Tcl_DriverThreadActionProc is defined for it.

       Tcl_ClearChannelHandlers removes all channel handlers and event scripts
       associated with the specified channel, thus shutting down all event
       processing for this channel.

TCL_CHANNELTYPE
       A channel driver provides a Tcl_ChannelType structure that contains
       pointers to functions that implement the various operations on a
       channel; these operations are invoked as needed by the generic layer.
       The structure was versioned starting in Tcl 8.3.2/8.4 to correct a
       problem with stacked channel drivers.  See the OLD CHANNEL TYPES
       section below for details about the old structure.

       The Tcl_ChannelType structure contains the following fields:

              typedef struct Tcl_ChannelType {
                      const char *typeName;
                      Tcl_ChannelTypeVersion version;
                      Tcl_DriverCloseProc *closeProc;
                      Tcl_DriverInputProc *inputProc;
                      Tcl_DriverOutputProc *outputProc;
                      Tcl_DriverSeekProc *seekProc;
                      Tcl_DriverSetOptionProc *setOptionProc;
                      Tcl_DriverGetOptionProc *getOptionProc;
                      Tcl_DriverWatchProc *watchProc;
                      Tcl_DriverGetHandleProc *getHandleProc;
                      Tcl_DriverClose2Proc *close2Proc;
                      Tcl_DriverBlockModeProc *blockModeProc;
                      Tcl_DriverFlushProc *flushProc;
                      Tcl_DriverHandlerProc *handlerProc;
                      Tcl_DriverWideSeekProc *wideSeekProc;
                      Tcl_DriverThreadActionProc *threadActionProc;
                      Tcl_DriverTruncateProc *truncateProc;
              } Tcl_ChannelType;

       It is not necessary to provide implementations for all channel
       operations.  Those which are not necessary may be set to NULL in the
       struct: blockModeProc, seekProc, setOptionProc, getOptionProc,
       getHandleProc, and close2Proc, in addition to flushProc, handlerProc,
       threadActionProc, and truncateProc.  Other functions that cannot be
       implemented in a meaningful way should return EINVAL when called, to
       indicate that the operations they represent are not available. Also
       note that wideSeekProc can be NULL if seekProc is.

       The user should only use the above structure for Tcl_ChannelType
       instantiation.  When referencing fields in a Tcl_ChannelType structure,
       the following functions should be used to obtain the values:
       Tcl_ChannelName, Tcl_ChannelVersion, Tcl_ChannelBlockModeProc,
       Tcl_ChannelCloseProc, Tcl_ChannelClose2Proc, Tcl_ChannelInputProc,
       Tcl_ChannelOutputProc, Tcl_ChannelSeekProc, Tcl_ChannelWideSeekProc,
       Tcl_ChannelThreadActionProc, Tcl_ChannelTruncateProc,
       Tcl_ChannelSetOptionProc, Tcl_ChannelGetOptionProc,
       Tcl_ChannelWatchProc, Tcl_ChannelGetHandleProc, Tcl_ChannelFlushProc,
       or Tcl_ChannelHandlerProc.

       The change to the structures was made in such a way that standard
       channel types are binary compatible.  However, channel types that use
       stacked channels (i.e. TLS, Trf) have new versions to correspond to the
       above change since the previous code for stacked channels had problems.

   TYPENAME
       The typeName field contains a null-terminated string that identifies
       the type of the device implemented by this driver, e.g.  file or
       socket.

       This value can be retrieved with Tcl_ChannelName, which returns a
       pointer to the string.

   VERSION
       The version field should be set to the version of the structure that
       you require. TCL_CHANNEL_VERSION_2 is the minimum recommended.
       TCL_CHANNEL_VERSION_3 must be set to specify the wideSeekProc member.
       TCL_CHANNEL_VERSION_4 must be set to specify the threadActionProc
       member (includes wideSeekProc).  TCL_CHANNEL_VERSION_5 must be set to
       specify the truncateProc members (includes wideSeekProc and
       threadActionProc).  If it is not set to any of these, then this
       Tcl_ChannelType is assumed to have the original structure.  See OLD
       CHANNEL TYPES for more details.  While Tcl will recognize and function
       with either structures, stacked channels must be of at least
       TCL_CHANNEL_VERSION_2 to function correctly.

       This value can be retrieved with Tcl_ChannelVersion, which returns one
       of TCL_CHANNEL_VERSION_5, TCL_CHANNEL_VERSION_4, TCL_CHANNEL_VERSION_3,
       TCL_CHANNEL_VERSION_2 or TCL_CHANNEL_VERSION_1.

   BLOCKMODEPROC
       The blockModeProc field contains the address of a function called by
       the generic layer to set blocking and nonblocking mode on the device.
       BlockModeProc should match the following prototype:

              typedef int Tcl_DriverBlockModeProc(
                      ClientData instanceData,
                      int mode);

       The instanceData is the same as the value passed to Tcl_CreateChannel
       when this channel was created.  The mode argument is either
       TCL_MODE_BLOCKING or TCL_MODE_NONBLOCKING to set the device into
       blocking or nonblocking mode. The function should return zero if the
       operation was successful, or a nonzero POSIX error code if the
       operation failed.

       If the operation is successful, the function can modify the supplied
       instanceData to record that the channel entered blocking or nonblocking
       mode and to implement the blocking or nonblocking behavior.  For some
       device types, the blocking and nonblocking behavior can be implemented
       by the underlying operating system; for other device types, the
       behavior must be emulated in the channel driver.

       This value can be retrieved with Tcl_ChannelBlockModeProc, which
       returns a pointer to the function.

       A channel driver not supplying a blockModeProc has to be very, very
       careful. It has to tell the generic layer exactly which blocking mode
       is acceptable to it, and should this also document for the user so that
       the blocking mode of the channel is not changed to an unacceptable
       value. Any confusion here may lead the interpreter into a (spurious and
       difficult to find) deadlock.

   CLOSEPROC AND CLOSE2PROC
       The closeProc field contains the address of a function called by the
       generic layer to clean up driver-related information when the channel
       is closed. CloseProc must match the following prototype:

              typedef int Tcl_DriverCloseProc(
                      ClientData instanceData,
                      Tcl_Interp *interp);

       The instanceData argument is the same as the value provided to
       Tcl_CreateChannel when the channel was created. The function should
       release any storage maintained by the channel driver for this channel,
       and close the input and output devices encapsulated by this channel.
       All queued output will have been flushed to the device before this
       function is called, and no further driver operations will be invoked on
       this instance after calling the closeProc. If the close operation is
       successful, the procedure should return zero; otherwise it should
       return a nonzero POSIX error code. In addition, if an error occurs and
       interp is not NULL, the procedure should store an error message in the
       interpreter's result.

       Alternatively, channels that support closing the read and write sides
       independently may set closeProc to TCL_CLOSE2PROC and set close2Proc to
       the address of a function that matches the following prototype:

              typedef int Tcl_DriverClose2Proc(
                      ClientData instanceData,
                      Tcl_Interp *interp,
                      int flags);

       The close2Proc will be called with flags set to an OR'ed combination of
       TCL_CLOSE_READ or TCL_CLOSE_WRITE to indicate that the driver should
       close the read and/or write side of the channel.  The channel driver
       may be invoked to perform additional operations on the channel after
       close2Proc is called to close one or both sides of the channel.  If
       flags is 0 (zero), the driver should close the channel in the manner
       described above for closeProc.  No further operations will be invoked
       on this instance after close2Proc is called with all flags cleared.  In
       all cases, the close2Proc function should return zero if the close
       operation was successful; otherwise it should return a nonzero POSIX
       error code. In addition, if an error occurs and interp is not NULL, the
       procedure should store an error message in the interpreter's result.

       The closeProc and close2Proc values can be retrieved with
       Tcl_ChannelCloseProc or Tcl_ChannelClose2Proc, which return a pointer
       to the respective function.

   INPUTPROC
       The inputProc field contains the address of a function called by the
       generic layer to read data from the file or device and store it in an
       internal buffer. InputProc must match the following prototype:

              typedef int Tcl_DriverInputProc(
                      ClientData instanceData,
                      char *buf,
                      int bufSize,
                      int *errorCodePtr);

       InstanceData is the same as the value passed to Tcl_CreateChannel when
       the channel was created.  The buf argument points to an array of bytes
       in which to store input from the device, and the bufSize argument
       indicates how many bytes are available at buf.

       The errorCodePtr argument points to an integer variable provided by the
       generic layer. If an error occurs, the function should set the variable
       to a POSIX error code that identifies the error that occurred.

       The function should read data from the input device encapsulated by the
       channel and store it at buf.  On success, the function should return a
       nonnegative integer indicating how many bytes were read from the input
       device and stored at buf. On error, the function should return -1. If
       an error occurs after some data has been read from the device, that
       data is lost.

       If inputProc can determine that the input device has some data
       available but less than requested by the bufSize argument, the function
       should only attempt to read as much data as is available and return
       without blocking. If the input device has no data available whatsoever
       and the channel is in nonblocking mode, the function should return an
       EAGAIN error. If the input device has no data available whatsoever and
       the channel is in blocking mode, the function should block for the
       shortest possible time until at least one byte of data can be read from
       the device; then, it should return as much data as it can read without
       blocking.

       This value can be retrieved with Tcl_ChannelInputProc, which returns a
       pointer to the function.

   OUTPUTPROC
       The outputProc field contains the address of a function called by the
       generic layer to transfer data from an internal buffer to the output
       device.  OutputProc must match the following prototype:

              typedef int Tcl_DriverOutputProc(
                      ClientData instanceData,
                      const char *buf,
                      int toWrite,
                      int *errorCodePtr);

       InstanceData is the same as the value passed to Tcl_CreateChannel when
       the channel was created. The buf argument contains an array of bytes to
       be written to the device, and the toWrite argument indicates how many
       bytes are to be written from the buf argument.

       The errorCodePtr argument points to an integer variable provided by the
       generic layer. If an error occurs, the function should set this
       variable to a POSIX error code that identifies the error.

       The function should write the data at buf to the output device
       encapsulated by the channel. On success, the function should return a
       nonnegative integer indicating how many bytes were written to the
       output device.  The return value is normally the same as toWrite, but
       may be less in some cases such as if the output operation is
       interrupted by a signal. If an error occurs the function should return
       -1.  In case of error, some data may have been written to the device.

       If the channel is nonblocking and the output device is unable to absorb
       any data whatsoever, the function should return -1 with an EAGAIN error
       without writing any data.

       This value can be retrieved with Tcl_ChannelOutputProc, which returns a
       pointer to the function.

   SEEKPROC AND WIDESEEKPROC
       The seekProc field contains the address of a function called by the
       generic layer to move the access point at which subsequent input or
       output operations will be applied. SeekProc must match the following
       prototype:

              typedef int Tcl_DriverSeekProc(
                      ClientData instanceData,
                      long offset,
                      int seekMode,
                      int *errorCodePtr);

       The instanceData argument is the same as the value given to
       Tcl_CreateChannel when this channel was created.  Offset and seekMode
       have the same meaning as for the Tcl_Seek procedure (described in the
       manual entry for Tcl_OpenFileChannel).

       The errorCodePtr argument points to an integer variable provided by the
       generic layer for returning errno values from the function.  The
       function should set this variable to a POSIX error code if an error
       occurs.  The function should store an EINVAL error code if the channel
       type does not implement seeking.

       The return value is the new access point or -1 in case of error. If an
       error occurred, the function should not move the access point.

       If there is a non-NULL seekProc field, the wideSeekProc field may
       contain the address of an alternative function to use which handles
       wide (i.e. larger than 32-bit) offsets, so allowing seeks within files
       larger than 2GB.  The wideSeekProc will be called in preference to the
       seekProc, but both must be defined if the wideSeekProc is defined.
       WideSeekProc must match the following prototype:

              typedef Tcl_WideInt Tcl_DriverWideSeekProc(
                      ClientData instanceData,
                      Tcl_WideInt offset,
                      int seekMode,
                      int *errorCodePtr);

       The arguments and return values mean the same thing as with seekProc
       above, except that the type of offsets and the return type are
       different.

       The seekProc value can be retrieved with Tcl_ChannelSeekProc, which
       returns a pointer to the function, and similarly the wideSeekProc can
       be retrieved with Tcl_ChannelWideSeekProc.

   SETOPTIONPROC
       The setOptionProc field contains the address of a function called by
       the generic layer to set a channel type specific option on a channel.
       setOptionProc must match the following prototype:

              typedef int Tcl_DriverSetOptionProc(
                      ClientData instanceData,
                      Tcl_Interp *interp,
                      const char *optionName,
                      const char *newValue);

       optionName is the name of an option to set, and newValue is the new
       value for that option, as a string. The instanceData is the same as the
       value given to Tcl_CreateChannel when this channel was created. The
       function should do whatever channel type specific action is required to
       implement the new value of the option.

       Some options are handled by the generic code and this function is never
       called to set them, e.g. -blockmode. Other options are specific to each
       channel type and the setOptionProc procedure of the channel driver will
       get called to implement them. The setOptionProc field can be NULL,
       which indicates that this channel type supports no type specific
       options.

       If the option value is successfully modified to the new value, the
       function returns TCL_OK.  It should call Tcl_BadChannelOption which
       itself returns TCL_ERROR if the optionName is unrecognized.  If
       newValue specifies a value for the option that is not supported or if a
       system call error occurs, the function should leave an error message in
       the result field of interp if interp is not NULL. The function should
       also call Tcl_SetErrno to store an appropriate POSIX error code.

       This value can be retrieved with Tcl_ChannelSetOptionProc, which
       returns a pointer to the function.

   GETOPTIONPROC
       The getOptionProc field contains the address of a function called by
       the generic layer to get the value of a channel type specific option on
       a channel. getOptionProc must match the following prototype:

              typedef int Tcl_DriverGetOptionProc(
                      ClientData instanceData,
                      Tcl_Interp *interp,
                      const char *optionName,
                      Tcl_DString *optionValue);

       OptionName is the name of an option supported by this type of channel.
       If the option name is not NULL, the function stores its current value,
       as a string, in the Tcl dynamic string optionValue.  If optionName is
       NULL, the function stores in optionValue an alternating list of all
       supported options and their current values.  On success, the function
       returns TCL_OK.  It should call Tcl_BadChannelOption which itself
       returns TCL_ERROR if the optionName is unrecognized. If a system call
       error occurs, the function should leave an error message in the result
       of interp if interp is not NULL. The function should also call
       Tcl_SetErrno to store an appropriate POSIX error code.

       Some options are handled by the generic code and this function is never
       called to retrieve their value, e.g. -blockmode. Other options are
       specific to each channel type and the getOptionProc procedure of the
       channel driver will get called to implement them. The getOptionProc
       field can be NULL, which indicates that this channel type supports no
       type specific options.

       This value can be retrieved with Tcl_ChannelGetOptionProc, which
       returns a pointer to the function.

   WATCHPROC
       The watchProc field contains the address of a function called by the
       generic layer to initialize the event notification mechanism to notice
       events of interest on this channel.  WatchProc should match the
       following prototype:

              typedef void Tcl_DriverWatchProc(
                      ClientData instanceData,
                      int mask);

       The instanceData is the same as the value passed to Tcl_CreateChannel
       when this channel was created. The mask argument is an OR-ed
       combination of TCL_READABLE, TCL_WRITABLE and TCL_EXCEPTION; it
       indicates events the caller is interested in noticing on this channel.

       The function should initialize device type specific mechanisms to
       notice when an event of interest is present on the channel.  When one
       or more of the designated events occurs on the channel, the channel
       driver is responsible for calling Tcl_NotifyChannel to inform the
       generic channel module.  The driver should take care not to starve
       other channel drivers or sources of callbacks by invoking
       Tcl_NotifyChannel too frequently.  Fairness can be insured by using the
       Tcl event queue to allow the channel event to be scheduled in sequence
       with other events.  See the description of Tcl_QueueEvent for details
       on how to queue an event.

       This value can be retrieved with Tcl_ChannelWatchProc, which returns a
       pointer to the function.

   GETHANDLEPROC
       The getHandleProc field contains the address of a function called by
       the generic layer to retrieve a device-specific handle from the
       channel.  GetHandleProc should match the following prototype:

              typedef int Tcl_DriverGetHandleProc(
                      ClientData instanceData,
                      int direction,
                      ClientData *handlePtr);

       InstanceData is the same as the value passed to Tcl_CreateChannel when
       this channel was created. The direction argument is either TCL_READABLE
       to retrieve the handle used for input, or TCL_WRITABLE to retrieve the
       handle used for output.

       If the channel implementation has device-specific handles, the function
       should retrieve the appropriate handle associated with the channel,
       according the direction argument.  The handle should be stored in the
       location referred to by handlePtr, and TCL_OK should be returned.  If
       the channel is not open for the specified direction, or if the channel
       implementation does not use device handles, the function should return
       TCL_ERROR.

       This value can be retrieved with Tcl_ChannelGetHandleProc, which
       returns a pointer to the function.

   FLUSHPROC
       The flushProc field is currently reserved for future use.  It should be
       set to NULL.  FlushProc should match the following prototype:

              typedef int Tcl_DriverFlushProc(
                      ClientData instanceData);

       This value can be retrieved with Tcl_ChannelFlushProc, which returns a
       pointer to the function.

   HANDLERPROC
       The handlerProc field contains the address of a function called by the
       generic layer to notify the channel that an event occurred.  It should
       be defined for stacked channel drivers that wish to be notified of
       events that occur on the underlying (stacked) channel.  HandlerProc
       should match the following prototype:

              typedef int Tcl_DriverHandlerProc(
                      ClientData instanceData,
                      int interestMask);

       InstanceData is the same as the value passed to Tcl_CreateChannel when
       this channel was created.  The interestMask is an OR-ed combination of
       TCL_READABLE or TCL_WRITABLE; it indicates what type of event occurred
       on this channel.

       This value can be retrieved with Tcl_ChannelHandlerProc, which returns
       a pointer to the function.


   THREADACTIONPROC
       The threadActionProc field contains the address of the function called
       by the generic layer when a channel is created, closed, or going to
       move to a different thread, i.e. whenever thread-specific driver state
       might have to initialized or updated. It can be NULL.  The action
       TCL_CHANNEL_THREAD_REMOVE is used to notify the driver that it should
       update or remove any thread-specific data it might be maintaining for
       the channel.

       The action TCL_CHANNEL_THREAD_INSERT is used to notify the driver that
       it should update or initialize any thread-specific data it might be
       maintaining using the calling thread as the associate. See
       Tcl_CutChannel and Tcl_SpliceChannel for more detail.

              typedef void Tcl_DriverThreadActionProc(
                      ClientData instanceData,
                      int action);

       InstanceData is the same as the value passed to Tcl_CreateChannel when
       this channel was created.

       These values can be retrieved with Tcl_ChannelThreadActionProc, which
       returns a pointer to the function.

   TRUNCATEPROC
       The truncateProc field contains the address of the function called by
       the generic layer when a channel is truncated to some length. It can be
       NULL.

              typedef int Tcl_DriverTruncateProc(
                      ClientData instanceData,
                      Tcl_WideInt length);

       InstanceData is the same as the value passed to Tcl_CreateChannel when
       this channel was created, and length is the new length of the
       underlying file, which should not be negative. The result should be 0
       on success or an errno code (suitable for use with Tcl_SetErrno) on
       failure.

       These values can be retrieved with Tcl_ChannelTruncateProc, which
       returns a pointer to the function.

TCL_BADCHANNELOPTION
       This procedure generates a “bad option” error message in an (optional)
       interpreter.  It is used by channel drivers when an invalid Set/Get
       option is requested. Its purpose is to concatenate the generic options
       list to the specific ones and factorize the generic options error
       message string.

       It always returns TCL_ERROR

       An error message is generated in interp's result value to indicate that
       a command was invoked with a bad option.  The message has the form
                  bad option "blah": should be one of
                  <...generic options...>+<...specific options...>
       so you get for instance:
                  bad option "-blah": should be one of -blocking,
                  -buffering, -buffersize, -eofchar, -translation,
                  -peername, or -sockname
       when called with optionList equal to “peername sockname”

       “blah” is the optionName argument and “<specific options>” is a space
       separated list of specific option words.  The function takes good care
       of inserting minus signs before each option, commas after, and an “or”
       before the last option.

OLD CHANNEL TYPES
       The original (8.3.1 and below) Tcl_ChannelType structure contains the
       following fields:

              typedef struct Tcl_ChannelType {
                  const char *typeName;
                  Tcl_DriverBlockModeProc *blockModeProc;
                  Tcl_DriverCloseProc *closeProc;
                  Tcl_DriverInputProc *inputProc;
                  Tcl_DriverOutputProc *outputProc;
                  Tcl_DriverSeekProc *seekProc;
                  Tcl_DriverSetOptionProc *setOptionProc;
                  Tcl_DriverGetOptionProc *getOptionProc;
                  Tcl_DriverWatchProc *watchProc;
                  Tcl_DriverGetHandleProc *getHandleProc;
                  Tcl_DriverClose2Proc *close2Proc;
              } Tcl_ChannelType;

       It is still possible to create channel with the above structure.  The
       internal channel code will determine the version.  It is imperative to
       use the new Tcl_ChannelType structure if you are creating a stacked
       channel driver, due to problems with the earlier stacked channel
       implementation (in 8.2.0 to 8.3.1).

       Prior to 8.4.0 (i.e. during the later releases of 8.3 and early part of
       the 8.4 development cycle) the Tcl_ChannelType structure contained the
       following fields:

              typedef struct Tcl_ChannelType {
                  const char *typeName;
                  Tcl_ChannelTypeVersion version;
                  Tcl_DriverCloseProc *closeProc;
                  Tcl_DriverInputProc *inputProc;
                  Tcl_DriverOutputProc *outputProc;
                  Tcl_DriverSeekProc *seekProc;
                  Tcl_DriverSetOptionProc *setOptionProc;
                  Tcl_DriverGetOptionProc *getOptionProc;
                  Tcl_DriverWatchProc *watchProc;
                  Tcl_DriverGetHandleProc *getHandleProc;
                  Tcl_DriverClose2Proc *close2Proc;
                  Tcl_DriverBlockModeProc *blockModeProc;
                  Tcl_DriverFlushProc *flushProc;
                  Tcl_DriverHandlerProc *handlerProc;
                  Tcl_DriverTruncateProc *truncateProc;
              } Tcl_ChannelType;

       When the above structure is registered as a channel type, the version
       field should always be TCL_CHANNEL_VERSION_2.

SEE ALSO
       Tcl_Close(3), Tcl_OpenFileChannel(3), Tcl_SetErrno(3),
       Tcl_QueueEvent(3), Tcl_StackChannel(3), Tcl_GetStdChannel(3)

KEYWORDS
       blocking, channel driver, channel registration, channel type,
       nonblocking



Tcl                                   8.4                 Tcl_CreateChannel(3)