Tcl_MutexFinalize(3tcl)
Threads(3) Tcl Library Procedures Threads(3)
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NAME
Tcl_ConditionNotify, Tcl_ConditionWait,
Tcl_ConditionFinalize, Tcl_GetThreadData, Tcl_MutexLock,
Tcl_MutexUnlock, Tcl_MutexFinalize, Tcl_CreateThread,
Tcl_JoinThread - 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)
int
Tcl_JoinThread(id, result)
ARGUMENTS
Tcl_Condition *condPtr (in) A condition
variable,
which must be
associated
with a mutex
lock.
Tcl_Mutex *mutexPtr (in) A mutex lock.
Tcl_Time *timePtr (in) A time limit
on the condi-
tion wait.
NULL to wait
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forever. Note
that a polling
value of 0
seconds does
not make much
sense.
Tcl_ThreadDataKey *keyPtr (in) This identi-
fies a block
of thread
local storage.
The key should
be static and
process-wide,
yet each
thread will
end up associ-
ating a dif-
ferent block
of storage
with this key.
int *size (in) The size of
the thread
local storage
block. This
amount of data
is allocated
and initial-
ized to zero
the first time
each thread
calls
Tcl_GetThreadData.
Tcl_ThreadId *idPtr (out) The referred
storage 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
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created
thread. The
specified
clientData
will be its
sole argument.
ClientData clientData (in) Arbitrary
information.
Passed as sole
argument to
the thread-
Proc.
int stackSize (in) The size of
the stack
given to the
new thread.
int flags (in) Bitmask con-
taining flags
allowing the
caller to
modify
behaviour of
the new
thread.
int *result (out) The referred
storage is
used to place
the exit code
of the thread
waited upon
into it.
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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 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, a single thread
can safely create and use multiple interpreters.)
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DESCRIPTION
Tcl provides 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 only the values TCL_THREAD_NOFLAGS and
TCL_THREAD_JOINABLE are defined. The first of them invokes
the default behaviour with no specialties. 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 stack size is ignored on
these systems. Windows currently does not support joinable
threads. This flag value is therefore ignored on this plat-
form.
Tcl provides the Tcl_ExitThread and Tcl_FinalizeThread func-
tions for terminating threads and invoking optional per-
thread exit handlers. See the Tcl_Exit page for more infor-
mation 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_CreateThread.
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 possi-
ble, the system will retain the necessary information until
after the call to Tcl_JoinThread. This means that not cal-
ling Tcl_JoinThread for a joinable thread will cause a
memory leak.
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.
SYNCHRONIZATION AND COMMUNICATION
Tcl provides Tcl_ThreadQueueEvent and Tcl_ThreadAlert for
handling event queuing in multithreaded applications. See
the Notifier manual page for more information on these pro-
cedures.
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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. 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_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.
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.
SCRIPT-LEVEL ACCESS TO THREADS
Tcl provides no built-in commands for scripts to use to |
create, manage, or join threads, nor any script-level access |
to mutex or condition variables. It provides such facili- |
ties only via C interfaces, and leaves it up to packages to |
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expose these matters to the script level. One such package |
is the Thread package.
SEE ALSO
Tcl_GetCurrentThread(3), Tcl_ThreadQueueEvent(3),
Tcl_ThreadAlert(3), Tcl_ExitThread(3),
Tcl_FinalizeThread(3), Tcl_CreateThreadExitHandler(3),
Tcl_DeleteThreadExitHandler(3), Thread
KEYWORDS
thread, mutex, condition variable, thread local storage
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