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Threads(3) Tcl Library Procedures Threads(3) 





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 forever. 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 created 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 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 platform.


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
    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 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 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 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_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 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_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_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 facilities only via C interfaces, 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_FinalizeThread(3),
    Tcl_CreateThreadExitHandler(3), Tcl_DeleteThreadExitHandler(3), Thread






KEYWORDS


thread, mutex, condition variable, thread local storage







  

    8.1
    Tcl