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Tcl_ChannelGetHandleProc(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_Channel-
       BlockModeProc,  Tcl_ChannelCloseProc,  Tcl_ChannelClose2Proc, Tcl_Chan-
       nelInputProc, Tcl_ChannelOutputProc, Tcl_ChannelSeekProc,  Tcl_Channel-
       WideSeekProc,    Tcl_ChannelSetOptionProc,    Tcl_ChannelGetOptionProc,
       Tcl_ChannelWatchProc,  Tcl_ChannelGetHandleProc,  Tcl_ChannelFlushProc,
       Tcl_ChannelHandlerProc,     Tcl_ChannelThreadActionProc,    Tcl_IsChan-
       nelShared, 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)

       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_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

       Tcl_ChannelType   *typePtr       (in)      Points  to  a structure con-
                                                  taining  the  addresses   of
                                                  procedures   that   can   be
                                                  called to  perform  I/O  and
                                                  other functions on the chan-
                                                  nel.

       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 with-
                                                  out a name.

       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 read-
                                                  able 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  out-
                                                  put handle is wanted.

       ClientData        *handlePtr     (out)     Points to the location where
                                                  the desired OS-specific han-
                                                  dle 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 indi-
                                                  cates   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 stan-
                                                  dard 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_OpenFileChan-
       nel.

       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-spe-
       cific 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  chan-
       nel  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  com-
       mand  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 type-
       Ptr and instanceData with it. The channel is opened in the  mode  indi-
       cated  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 chan-
       nels. 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 behaviour 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 han-
       dlePtr and returns TCL_OK.  If the channel does not have a device  han-
       dle  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 out-
       put.

       Tcl_GetChannelBufferSize returns the size, in bytes, of  buffers  allo-
       cated  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 ten and one million, allow-
       ing buffers of ten bytes 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 set or get option
       procs 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 regis- |
       tered 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 reg-
       istered 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 channelhandlers 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 chan-
       nel; 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 {
                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_ChannelType;

       It  is  not necessary to provide implementations for all channel opera-
       tions.  Those which are not necessary may be set to NULL in the struct:
       blockModeProc,  seekProc, setOptionProc, getOptionProc, and close2Proc,
       in addition to flushProc,  handlerProc,  and  threadActionProc.   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_Chan-
       nelName,   Tcl_ChannelVersion,  Tcl_ChannelBlockModeProc,  Tcl_Channel-
       CloseProc, Tcl_ChannelClose2Proc, Tcl_ChannelInputProc, Tcl_ChannelOut-
       putProc,    Tcl_ChannelSeekProc,   Tcl_ChannelWideSeekProc,   Tcl_Chan- |
       nelThreadActionProc,  Tcl_ChannelSetOptionProc,   Tcl_ChannelGetOption-
       Proc, Tcl_ChannelWatchProc, Tcl_ChannelGetHandleProc, Tcl_ChannelFlush-
       Proc, or Tcl_ChannelHandlerProc.

       The change to the structures was made in such a way that standard chan-
       nel  types  are  binary  compatible.   However,  channel types that use
       stacked channels (ie: 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 specifiy the wideSeekProc member. |
       TCL_CHANNEL_VERSION_4 must be set to specifiy the threadActionProc mem- |
       ber  (includes  wideSeekProc).   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 func-
       tion 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_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 block-
       ing or nonblocking mode. The function should return zero if the  opera-
       tion  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  behav-
       ior 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 inacceptable
       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_Cre-
       ateChannel 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 suc-
       cessful, 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  inter-
       preter'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.

       These value can be retrieved with Tcl_ChannelCloseProc or  Tcl_Channel-
       Close2Proc, which returns 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 indi-
       cates 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 avail-
       able 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 vari-
       able to a POSIX error code that identifies the error.

       The function should write the data at buf to the output device encapsu-
       lated by the channel. On success, the function should return a nonnega-
       tive 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_Create-
       Channel  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  func-
       tion 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  con- |
       tain  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  differ- |
       ent.                                                                    |

       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  new-
       Value  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 spe-
       cific to each channel type and the getOptionProc procedure of the chan-
       nel  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 follow-
       ing 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  combina-
       tion  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_Notify-
       Channel 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 chan-
       nel.  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_CutChan- |
       nel 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.


TCL_BADCHANNELOPTION

       This  procedure generates a "bad option" error message in an (optional)
       interpreter.  It is used by channel  drivers  when  a  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  mes-
       sage string.

       It always return TCL_ERROR

       An  error  message  is  generated in interp's result object to indicate
       that a command was invoked with the 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="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 {
                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 imple-
       mentation (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 {                                 |
                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_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, nonblock-
       ing

Tcl                                   8.4                 Tcl_CreateChannel(3)

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