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Tcl_CreateChannel(3) Tcl Library Procedures Tcl_CreateChannel(3)
__________________________________________________________________________________________
NAME
Tcl_CreateChannel, Tcl_GetChannelInstanceData, Tcl_GetChannelType, Tcl_GetChannel-
Name, Tcl_GetChannelHandle, Tcl_GetChannelMode, Tcl_GetChannelBufferSize,
Tcl_SetChannelBufferSize, Tcl_NotifyChannel, Tcl_BadChannelOption, Tcl_ChannelName,
Tcl_ChannelVersion, Tcl_ChannelBlockModeProc, Tcl_ChannelCloseProc, Tcl_Channel-
Close2Proc, Tcl_ChannelInputProc, Tcl_ChannelOutputProc, Tcl_ChannelSeekProc,
Tcl_ChannelWideSeekProc, Tcl_ChannelSetOptionProc, Tcl_ChannelGetOptionProc,
Tcl_ChannelWatchProc, Tcl_ChannelGetHandleProc, Tcl_ChannelFlushProc, Tcl_Channel-
HandlerProc, Tcl_ChannelThreadActionProc, Tcl_IsChannelShared, Tcl_IsChannelRegis-
tered, Tcl_CutChannel, Tcl_SpliceChannel, Tcl_IsChannelExisting, Tcl_ClearChannel-
Handlers, 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 containing the
addresses of procedures that can be
called to perform I/O and other func-
tions 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.
ClientData instanceData (in) Arbitrary one-word value to be associ-
ated 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 chan-
nel 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 allo-
cate 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 sup-
ported on each platform. This manual entry describes the C APIs used to communi-
cate 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 pro-
vides 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
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_Create-
Channel 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 chan-
nel, 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 ten and one million, allowing 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 gen-
erate 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 regis- |
tered 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 ver- |
sion 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 chan-
nel.
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 CHAN-
NEL 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 operations. Those
which are not necessary may be set to NULL in the struct: blockModeProc, seekProc,
setOptionProc, getOptionProc, and close2Proc, in addition to flushProc, handler-
Proc, and threadActionProc. Other functions that cannot be implemented in a mean-
ingful 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_Chan-
nelBlockModeProc, Tcl_ChannelCloseProc, Tcl_ChannelClose2Proc, Tcl_ChannelInput-
Proc, Tcl_ChannelOutputProc, Tcl_ChannelSeekProc, Tcl_ChannelWideSeekProc, |
Tcl_ChannelThreadActionProc, Tcl_ChannelSetOptionProc, Tcl_ChannelGetOptionProc,
Tcl_ChannelWatchProc, Tcl_ChannelGetHandleProc, Tcl_ChannelFlushProc, or Tcl_Chan-
nelHandlerProc.
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 (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 member (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 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_CHAN- |
NEL_VERSION_4, TCL_CHANNEL_VERSION_3, TCL_CHANNEL_VERSION_2, or TCL_CHANNEL_VER-
SION_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 func-
tion 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 non-
blocking 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 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_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 encap-
sulated 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 chan-
nel 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 suc-
cessful; 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_ChannelClose2Proc,
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 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_Create-
Channel 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 sup-
ports no type specific options.
If the option value is successfully modified to the new value, the function returns
TCL_OK. It should call Tcl_BadChannelOption which itself returns TCL_ERROR if the
optionName is unrecognized. If newValue specifies a value for the option that is
not supported or if a system call error occurs, the function should leave an error
message in the result field of interp if interp is not NULL. The function should
also call Tcl_SetErrno to store an appropriate POSIX error code.
This value can be retrieved with Tcl_ChannelSetOptionProc, which returns a pointer
to the function.
GETOPTIONPROC
The getOptionProc field contains the address of a function called by the generic
layer to get the value of a channel type specific option on a channel. getOption-
Proc 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 appro-
priate 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 direc-
tion argument. The handle should be stored in the location referred to by han-
dlePtr, and TCL_OK should be returned. If the channel is not open for the speci-
fied 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 under-
lying (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.
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 pur-
pose is to concatenate the generic options list to the specific ones and factorize
the generic options error message 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_Chan-
nelType 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 { |
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, nonblocking
Tcl 8.4 Tcl_CreateChannel(3)
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