Index of Section 3 Manual Pages
| Interix / SUA | Tcl_ConditionWait.3 | Interix / SUA |
Threads(3) Tcl Library Procedures Threads(3)
_________________________________________________________________
NAME
Tcl_ConditionNotify, Tcl_ConditionWait, Tcl_ConditionFi-
nalize, Tcl_GetThreadData, Tcl_MutexLock, Tcl_MutexUnlock,
Tcl_MutexFinalize, Tcl_CreateThread, Tcl_JoinThread - Tcl
thread support.
SYNOPSIS
#include
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)
int
Tcl_JoinThread(id, result)
ARGUMENTS
Tcl_Condition *condPtr (in) A condition vari-
able, which must
be associated with
a mutex lock.
Tcl_Mutex *mutexPtr (in) A mutex lock.
Tcl_Time *timePtr (in) A time limit on
the condition
wait. NULL to
wait forever.
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 pro-
cess-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 stor-
age block. This
amount of data is
allocated and ini-
tialized to zero
the first time
each thread calls
Tcl_GetThreadData.
Tcl_ThreadId *idPtr (out) The referred stor-
age will contain
the id of the
newly created
thread as returned
by the operating
system.
Tcl_ThreadId id (in) Id of the thread
waited upon.
Tcl_ThreadCreateProc threadProc(in)
This procedure
will act as the
main() of the
newly created
thread. The speci-
fied clientData
will be its sole
argument.
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.
int *result (out) The referred stor-
age is used to
place the exit
code of the thread
waited upon into
it.
_________________________________________________________________
INTRODUCTION
Beginning with the 8.1 release, the Tcl core is thread
safe, which allows you to incorporate Tcl into multi-
threaded 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 constraint 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 sup- |
plied flags. The value TCL_THREAD_STACK_DEFAULT for the |
stackSize indicates 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 spe- |
cialties. 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 stack- |
size of a thread. The specified value for the stacksize is |
ignored on these systems. Both Windows and Macintosh cur- |
rently 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.
The Tcl_JoinThread function is provided to allow threads |
to wait upon the exit of another thread, which must have |
been marked as joinable through usage of the |
TCL_THREAD_JOINABLE-flag during its creation via Tcl_Cre- |
ateThread. |
Trying to wait for the exit of a non-joinable thread or a |
thread which is already waited upon will result in an |
error. Waiting for a joinable thread which already exited |
is possible, the system will retain the necessary informa- |
tion until after the call to Tcl_JoinThread. This means |
that not calling Tcl_JoinThread for a joinable thread will |
cause a memory leak.
Tcl provides Tcl_ThreadQueueEvent and Tcl_ThreadAlert for
handling event queueing in multithreaded applications.
See the Notifier manual page for more information on these
procedures.
In this release, the Tcl language itself provides no sup-
port 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 distribu-
tion for an experimental implementation or use the Tcl
"Threading Extension" package implementing 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_MutexUn-
lock 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 plat- |
forms 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. For declaration of mutexes the TCL_DECLARE_MUTEX
macro should be used. This macro assures correct mutex
handling even when the core is compiled without 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_Con-
ditionNotify should have the associated mutex held by pre-
viously calling Tcl_MutexLock, but this is not enforced.
Notifying the condition variable unblocks all threads
waiting on the condition variable, but they do not proceed
until the mutex is released with Tcl_MutexUnlock. The
implementation 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 |
calling Tcl_ConditionFinalize. |
The Tcl_ConditionNotify, Tcl_ConditionWait and Tcl_Condi- |
tionFinalize 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 initializ-
ing. They are implemented as opaque pointers that should
be NULL upon first use. The mutexes and condition vari-
ables are either cleaned up by process exit handlers (if |
living that long) or explicitly by calls to Tcl_MutexFi- |
nalize 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 con-
tain 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
Tcl 8.1 Threads(3)