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NAME
Tcl_ConditionNotify, Tcl_ConditionWait,
Tcl_ConditionFinalize, Tcl_GetThreadData, Tcl_MutexLock,
Tcl_MutexUnlock, Tcl_MutexFinalize - Tcl thread support.
SYNOPSIS
#include <tcl.h>
void
Tcl_ConditionNotify(condPtr)
void
Tcl_ConditionWait(condPtr, mutexPtr, timePtr)
void
Tcl_ConditionFinalize(condPtr)
Void *
Tcl_GetThreadData(keyPtr, size)
void
Tcl_MutexLock(mutexPtr)
void
Tcl_MutexUnlock(mutexPtr)
void
Tcl_MutexFinalize(mutexPtr)
int
Tcl_CreateThread(idPtr, threadProc, clientData, stackSize, flags)
ARGUMENTS
Tcl_Condition *condPtr (in) A condition vari-
able, which must be
associated with a
mutex lock.
Tcl_Condition *mutexPtr (in) A mutex lock.
Tcl_Time *timePtr (in) A time limit on the
condition wait.
NULL to wait for-
ever. Note that a
polling value of 0
seconds doesn't make
much sense.
Tcl_ThreadDataKey *keyPtr (in) This identifies a
block of thread
local storage. The
key should be static
and process-wide,
yet each thread will
end up associating a
different block of
storage with this
key.
int *size (in) The size of the
thread local storage
block. This amount
of data is allocated
and initialized to
zero the first time
each thread calls
Tcl_GetThreadData.
Tcl_ThreadId *idPtr (out) The refered storage
will contain the id
of the newly created
thread as returned
by the operating
system.
Tcl_ThreadCreateProc threadProc(in)
This procedure will
act as the main() of
the newly created
thread. The speci-
fied clientData will
be its sole argu-
ment.
ClientData clientData(in) Arbitrary informa-
tion. Passed as sole
argument to the
threadProc.
int stackSize (in) The size of the
stack given to the
new thread.
int flags (in) Bitmask containing
flags allowing the
caller to modify
behaviour of the new
thread.
_________________________________________________________________
INTRODUCTION
Beginning with the 8.1 release, the Tcl core is thread safe,
which allows you to incorporate Tcl into multithreaded
applications without customizing the Tcl core. To enable
Tcl multithreading support, you must include the --enable-
threads option to configure when you configure and compile
your Tcl core.
An important contstraint of the Tcl threads implementation
is that only the thread that created a Tcl interpreter can
use that interpreter. In other words, multiple threads can
not access the same Tcl interpreter. (However, as was the
case in previous releases, a single thread can safely create
and use multiple interpreters.)
Tcl does provide Tcl_CreateThread for creating threads. The |
caller can determine the size of the stack given to the new |
thread and modify the behaviour through the supplied flags. |
The value TCL_THREAD_STACK_DEFAULT for the stackSize indi- |
cates that the default size as specified by the operating |
system is to be used for the new thread. As for the flags, |
currently are only the values TCL_THREAD_NOFLAGS and |
TCL_THREAD_JOINABLE defined. The first of them invokes the |
default behaviour with no specialities. Using the second |
value marks the new thread as joinable. This means that |
another thread can wait for the such marked thread to exit |
and join it. |
Restrictions: On some unix systems the pthread-library does |
not contain the functionality to specify the stacksize of a |
thread. The specified value for the stacksize is ignored on |
these systems. Both Windows and Macintosh currently do not |
support joinable threads. This flag value is therefore |
ignored on these platforms.
Tcl does provide Tcl_ExitThread and Tcl_FinalizeThread for
terminating threads and invoking optional per-thread exit
handlers. See the Tcl_Exit page for more information on
these procedures.
Tcl provides Tcl_ThreadQueueEvent and Tcl_ThreadAlert for
handling event queueing in multithreaded applications. See
the Notifier manual page for more information on these pro-
cedures.
In this release, the Tcl language itself provides no support
for creating multithreaded scripts (for example, scripts
that could spawn a Tcl interpreter in a separate thread).
If you need to add this feature at this time, see the
tclThreadTest.c file in the Tcl source distribution for an
experimental implementation of a Tcl "Thread" package imple-
menting thread creation and management commands at the
script level.
DESCRIPTION
A mutex is a lock that is used to serialize all threads
through a piece of code by calling Tcl_MutexLock and
Tcl_MutexUnlock. If one thread holds a mutex, any other
thread calling Tcl_MutexLock will block until
Tcl_MutexUnlock is called. A mutex can be destroyed after |
its use by calling Tcl_MutexFinalize. The result of locking |
a mutex twice from the same thread is undefined. On some |
platforms it will result in a deadlock. The Tcl_MutexLock,
Tcl_MutexUnlock and Tcl_MutexFinalize procedures are defined
as empty macros if not compiling with threads enabled.
A condition variable is used as a signaling mechanism: a
thread can lock a mutex and then wait on a condition vari-
able with Tcl_ConditionWait. This atomically releases the
mutex lock and blocks the waiting thread until another
thread calls Tcl_ConditionNotify. The caller of
Tcl_ConditionNotify should have the associated mutex held by
previously calling Tcl_MutexLock, but this is not enforced.
Notifying the condition variable unblocks all threads wait-
ing on the condition variable, but they do not proceed until
the mutex is released with Tcl_MutexUnlock. The implementa-
tion of Tcl_ConditionWait automatically locks the mutex
before returning.
The caller of Tcl_ConditionWait should be prepared for
spurious notifications by calling Tcl_ConditionWait within a
while loop that tests some invariant.
A condition variable can be destroyed after its use by cal- |
ling Tcl_ConditionFinalize. |
The Tcl_ConditionNotify, Tcl_ConditionWait and |
Tcl_ConditionFinalize procedures are defined as empty macros |
if not compiling with threads enabled.
The Tcl_GetThreadData call returns a pointer to a block of
thread-private data. Its argument is a key that is shared
by all threads and a size for the block of storage. The
storage is automatically allocated and initialized to all
zeros the first time each thread asks for it. The storage
is automatically deallocated by Tcl_FinalizeThread.
INITIALIZATION
All of these synchronization objects are self initializing.
They are implemented as opaque pointers that should be NULL
upon first use. The mutexes and condition variables are |
either cleaned up by process exit handlers (if living that |
long) or explicitly by calls to Tcl_MutexFinalize or |
Tcl_ConditionFinalize. Thread local storage is reclaimed
during Tcl_FinalizeThread.
CREATING THREADS
The API to create threads is not finalized at this time.
There are private facilities to create threads that contain
a new Tcl interpreter, and to send scripts among threads.
Dive into tclThreadTest.c and tclThread.c for examples.
SEE ALSO
Tcl_GetCurrentThread, Tcl_ThreadQueueEvent, Tcl_ThreadAlert,
Tcl_ExitThread, Tcl_FinalizeThread,
Tcl_CreateThreadExitHandler, Tcl_DeleteThreadExitHandler
KEYWORDS
thread, mutex, condition variable, thread local storage
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