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 (or
other pending tasks like a write flush should be performed). 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 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)
