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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 condition wait.  NULL to wait for-ever. forever.
                                                     ever.  Note that a polling value of 0 seconds does  not
                                                     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 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 cre-ated created
                                                     ated thread. The specified clientData will be its  sole
                                                     argument.

       ClientData clientData (in)                    Arbitrary  information.  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 storage 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
       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.)

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 indicates that the default size as specified by the oper-ating operating
       ating 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 behav-iour behaviour
       iour 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.  Win-dows Windows
       dows  currently does not support joinable threads. This flag value is therefore ignored on this plat-form. platform.
       form.

       Tcl provides the Tcl_ExitThread and Tcl_FinalizeThread functions 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 cre-ation creation
       ation 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 possible, the  system  will
       retain the necessary information until after the call to Tcl_JoinThread.  This means that not calling
       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  auto-matically automatically
       matically 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 procedures.

       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_MutexFi-nalize Tcl_MutexFinalize
       nalize 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 variable 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 waiting on the condition variable, but they do
       not proceed until the mutex is released with Tcl_MutexUnlock.  The implementation  of  Tcl_Condition-Wait Tcl_ConditionWait
       Wait automatically locks the mutex before returning.

       The  caller  of Tcl_ConditionWait should be prepared for spurious notifications by calling Tcl_Condi-tionWait Tcl_ConditionWait
       tionWait 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_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_Condi-tionFinalize. Tcl_ConditionFinalize.
       tionFinalize.  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 facilities only via C inter- |
       faces, and leaves it up to packages to 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_Final-izeThread(3), Tcl_FinalizeThread(3),
       izeThread(3), Tcl_CreateThreadExitHandler(3), Tcl_DeleteThreadExitHandler(3), Thread

KEYWORDS
       thread, mutex, condition variable, thread local storage



Tcl                                                  8.1                                          Threads(3)