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_Channel‐
BlockModeProc, Tcl_ChannelCloseProc, Tcl_ChannelClose2Proc, Tcl_Chan‐
nelInputProc, Tcl_ChannelOutputProc, Tcl_ChannelSeekProc, Tcl_Channel‐
WideSeekProc, Tcl_ChannelTruncateProc, Tcl_ChannelSetOptionProc,
Tcl_ChannelGetOptionProc, Tcl_ChannelWatchProc, Tcl_ChannelGetH‐
andleProc, Tcl_ChannelFlushProc, Tcl_ChannelHandlerProc, Tcl_Chan‐
nelThreadActionProc, 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 proce‐
dures that can be
called to perform I/O
and other functions on
the channel.
const char *channelName (in) The name of this chan‐
nel, 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 stan‐
dard channel.
ClientData instanceData (in) Arbitrary one-word
value to be associated
with this channel.
This value is passed
to procedures in type‐
Ptr when they are
invoked.
int mask (in) OR-ed combination of
TCL_READABLE and
TCL_WRITABLE to indi‐
cate 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 han‐
dle 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_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 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 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 one and one million, allow‐
ing 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 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 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 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 {
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 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, threadActionProc, and trun‐
cateProc. 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_ChannelTruncateProc, Tcl_ChannelSetOptionProc,
Tcl_ChannelGetOptionProc, Tcl_ChannelWatchProc, Tcl_ChannelGetH‐
andleProc, Tcl_ChannelFlushProc, 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 (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 mem‐
ber (includes wideSeekProc). TCL_CHANNEL_VERSION_5 must be set to
specify the truncateProc members (includes wideSeekProc and threadAc‐
tionProc). 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 struc‐
tures, 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 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 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_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.
The closeProc and close2Proc values can be retrieved with Tcl_Channel‐
CloseProc 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 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.
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 underly‐
ing file, which should not be negative. The result should be 0 on suc‐
cess 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 mes‐
sage 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 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 {
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 ALSOTcl_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)
