X-Git-Url: https://git.saurik.com/wxWidgets.git/blobdiff_plain/6fe7378863be6febaaab0e8aa855b51781351ac5..134198f1b773199b5506c302bf9510831d0319f5:/docs/latex/wx/thread.tex?ds=sidebyside

diff --git a/docs/latex/wx/thread.tex b/docs/latex/wx/thread.tex
index ada3f901b9..73ff763528 100644
--- a/docs/latex/wx/thread.tex
+++ b/docs/latex/wx/thread.tex
@@ -3,30 +3,13 @@
 A thread is basically a path of execution through a program. Threads are
 sometimes called {\it light-weight processes}, but the fundamental difference
 between threads and processes is that memory spaces of different processes are
-separated while all threads share the same address space. While it makes it
-much easier to share common data between several threads, it also makes much
-easier to shoot oneself in the foot, so careful use of synchronization objects
-such as \helpref{mutexes}{wxmutex} and/or \helpref{critical sections}{wxcriticalsection} is recommended.
+separated while all threads share the same address space. 
 
-There are two types of threads in wxWindows: {\it detached} and {\it joinable}
-ones, just as in the POSIX thread API (but unlike Win32 threads where all threads
-are joinable). The difference between the two is that only joinable threads
-can return a return code - this is returned by the Wait() function. Detached
-threads (the default type) cannot be waited for.
-
-You shouldn't hurry to create all the threads joinable, however, because this
-has a disadvantage as well: you {\bf must} Wait() for a joinable thread or the
-system resources used by it will never be freed, and you also must delete the
-corresponding wxThread object yourself. In contrast, detached threads are of the
-"fire-and-forget" kind: you only have to start a detached thread and it will
-terminate and destroy itself.
-
-This means, of course, that all detached threads {\bf must} be created on the
-heap because the thread will call {\tt delete this;} upon termination. Joinable
-threads may be created on the stack although more usually they will be created
-on the heap as well. Don't create global thread objects because they allocate
-memory in their constructor, which will cause problems for the memory checking
-system.
+While it makes it much easier to share common data between several threads, it also 
+makes it much easier to shoot oneself in the foot, so careful use of synchronization 
+objects such as \helpref{mutexes}{wxmutex} or \helpref{critical sections}{wxcriticalsection} is recommended. In addition, don't create global thread 
+objects because they allocate memory in their constructor, which will cause 
+problems for the memory checking system.
 
 \wxheading{Derived from}
 
@@ -36,34 +19,135 @@ None.
 
 <wx/thread.h>
 
+\wxheading{Library}
+
+\helpref{wxBase}{librarieslist}
+
 \wxheading{See also}
 
 \helpref{wxMutex}{wxmutex}, \helpref{wxCondition}{wxcondition}, \helpref{wxCriticalSection}{wxcriticalsection}
 
 \latexignore{\rtfignore{\wxheading{Members}}}
 
+\membersection{Types of wxThreads}\label{typeswxthread}
+
+There are two types of threads in wxWidgets: {\it detached} and {\it joinable},
+modeled after the the POSIX thread API. This is different from the Win32 API
+where all threads are joinable. 
+
+By default wxThreads in wxWidgets use the detached behavior. Detached threads
+delete themselves once they have completed, either by themselves when they complete 
+processing or through a call to \helpref{wxThread::Delete}{wxthreaddelete}, and thus 
+must be created on the heap (through the new operator, for example). Conversely, 
+joinable threads do not delete themselves when they are done processing and as such
+are safe to create on the stack. Joinable threads also provide the ability
+for one to get value it returned from \helpref{wxThread::Entry}{wxthreadentry}
+through \helpref{wxThread::Wait}{wxthreadwait}.
+
+You shouldn't hurry to create all the threads joinable, however, because this
+has a disadvantage as well: you {\bf must} Wait() for a joinable thread or the
+system resources used by it will never be freed, and you also must delete the
+corresponding wxThread object yourself if you did not create it on the stack. In 
+contrast, detached threads are of the "fire-and-forget" kind: you only have to start 
+a detached thread and it will terminate and destroy itself.
+
+\membersection{wxThread deletion}\label{deletionwxthread}
+
+Regardless of whether it has terminated or not, you should call 
+\helpref{wxThread::Wait}{wxthreadwait} on a joinable thread to release its
+memory, as outlined in \helpref{Types of wxThreads}{typeswxthread}. If you created
+a joinable thread on the heap, remember to delete it manually with the delete 
+operator or similar means as only detached threads handle this type of memory 
+management.
+
+Since detached threads delete themselves when they are finished processing,
+you should take care when calling a routine on one. If you are certain the 
+thread is still running and would like to end it, you may call 
+\helpref{wxThread::Delete}{wxthreaddelete} to gracefully end it (which implies
+that the thread will be deleted after that call to Delete()). It should be
+implied that you should never attempt to delete a detached thread with the 
+delete operator or similar means. 
+
+As mentioned, \helpref{wxThread::Wait}{wxthreadwait} or 
+\helpref{wxThread::Delete}{wxthreaddelete} attempts to gracefully terminate
+a joinable and detached thread, respectively. It does this by waiting until
+the thread in question calls \helpref{wxThread::TestDestroy}{wxthreadtestdestroy}
+or ends processing (returns from \helpref{wxThread::Entry}{wxthreadentry}).
+
+Obviously, if the thread does call TestDestroy() and does not end the calling
+thread will come to halt. This is why it is important to call TestDestroy() in
+the Entry() routine of your threads as often as possible.
+
+As a last resort you can end the thread immediately through 
+\helpref{wxThread::Kill}{wxthreadkill}. It is strongly recommended that you
+do not do this, however, as it does not free the resources associated with
+the object (although the wxThread object of detached threads will still be
+deleted) and could leave the C runtime library in an undefined state.
+
+\membersection{wxWidgets calls in secondary threads}\label{secondarywxthread}
+
+All threads other then the "main application thread" (the one
+\helpref{wxApp::OnInit}{wxapponinit} or your main function runs in, for 
+example) are considered "secondary threads". These include all threads created 
+by \helpref{wxThread::Create}{wxthreadcreate} or the corresponding constructors.
+
+GUI calls, such as those to a \helpref{wxWindow}{wxwindow} or 
+\helpref{wxBitmap}{wxbitmap} are explicitly not safe at all in secondary threads 
+and could end your application prematurely. This is due to several reasons,
+including the underlying native API and the fact that wxThread does not run a 
+GUI event loop similar to other APIs as MFC. 
+
+A workaround that works on some wxWidgets ports is calling \helpref{wxMutexGUIEnter}{wxmutexguienter} 
+before any GUI calls and then calling \helpref{wxMutexGUILeave}{wxmutexguileave} afterwords. However,
+the recommended way is to simply process the GUI calls in the main thread 
+through an event that is posted by either \helpref{wxPostEvent}{wxpostevent} or
+\helpref{wxEvtHandler::AddPendingEvent}{wxevthandleraddpendingevent}. This does 
+not imply that calls to these classes are thread-safe, however, as most 
+wxWidgets classes are not thread-safe, including wxString.
+
+\membersection{Don't poll a wxThread}\label{dontpollwxthread}
+
+A common problem users experience with wxThread is that in their main thread
+they will check the thread every now and then to see if it has ended through
+\helpref{wxThread::IsRunning}{wxthreadisrunning}, only to find that their 
+application has run into problems because the thread is using the default
+behavior and has already deleted itself. Naturally, they instead attempt to
+use joinable threads in place of the previous behavior.
+
+However, polling a wxThread for when it has ended is in general a bad idea -
+in fact calling a routine on any running wxThread should be avoided if 
+possible. Instead, find a way to notify yourself when the thread has ended.
+Usually you only need to notify the main thread, in which case you can post
+an event to it via \helpref{wxPostEvent}{wxpostevent} or
+\helpref{wxEvtHandler::AddPendingEvent}{wxevthandleraddpendingevent}. In 
+the case of secondary threads you can call a routine of another class
+when the thread is about to complete processing and/or set the value
+of a variable, possibly using \helpref{mutexes}{wxmutex} and/or other 
+synchronization means if necessary.
+
 \membersection{wxThread::wxThread}\label{wxthreadctor}
 
 \func{}{wxThread}{\param{wxThreadKind }{kind = wxTHREAD\_DETACHED}}
 
 This constructor creates a new detached (default) or joinable C++ thread object. It
-does not create or start execution of the real thread - for this you should
+does not create or start execution of the real thread -- for this you should
 use the \helpref{Create}{wxthreadcreate} and \helpref{Run}{wxthreadrun} methods.
 
 The possible values for {\it kind} parameters are:
 
 \twocolwidtha{7cm}
 \begin{twocollist}\itemsep=0pt
-\twocolitem{{\bf wxTHREAD\_DETACHED}}{Create a detached thread.}
-\twocolitem{{\bf wxTHREAD\_JOINABLE}}{Create a joinable thread}
+\twocolitem{{\bf wxTHREAD\_DETACHED}}{Creates a detached thread.}
+\twocolitem{{\bf wxTHREAD\_JOINABLE}}{Creates a joinable thread.}
 \end{twocollist}
 
-\membersection{wxThread::\destruct{wxThread}}
+
+\membersection{wxThread::\destruct{wxThread}}\label{wxthreaddtor}
 
 \func{}{\destruct{wxThread}}{\void}
 
 The destructor frees the resources associated with the thread. Notice that you
-should never delete a detached thread - you may only call 
+should never delete a detached thread -- you may only call
 \helpref{Delete}{wxthreaddelete} on it or wait until it terminates (and auto
 destructs) itself. Because the detached threads delete themselves, they can
 only be allocated on the heap.
@@ -72,6 +156,7 @@ Joinable threads should be deleted explicitly. The \helpref{Delete}{wxthreaddele
 will not delete the C++ thread object. It is also safe to allocate them on
 stack.
 
+
 \membersection{wxThread::Create}\label{wxthreadcreate}
 
 \func{wxThreadError}{Create}{\param{unsigned int }{stackSize = 0}}
@@ -79,7 +164,22 @@ stack.
 Creates a new thread. The thread object is created in the suspended state, and you
 should call \helpref{Run}{wxthreadrun} to start running it.  You may optionally
 specify the stack size to be allocated to it (Ignored on platforms that don't
-support setting it explicitly, eg. Unix).
+support setting it explicitly, eg. Unix system without
+\texttt{pthread\_attr\_setstacksize}). If you do not specify the stack size,
+the system's default value is used.
+
+{\bf Warning:} It is a good idea to explicitly specify a value as systems'
+default values vary from just a couple of KB on some systems (BSD and
+OS/2 systems) to one or several MB (Windows, Solaris, Linux). So, if you
+have a thread that requires more than just a few KB of memory, you will
+have mysterious problems on some platforms but not on the common ones. On the
+other hand, just indicating a large stack size by default will give you
+performance issues on those systems with small default stack since those
+typically use fully committed memory for the stack. On the contrary, if
+use a lot of threads (say several hundred), virtual adress space can get tight
+unless you explicitly specify a smaller amount of thread stack space for each
+thread.
+
 
 \wxheading{Return value}
 
@@ -92,37 +192,21 @@ One of:
 \twocolitem{{\bf wxTHREAD\_RUNNING}}{The thread is already running.}
 \end{twocollist}
 
-\membersection{wxThread::Delete}\label{wxthreaddelete}
-
-\func{void}{Delete}{\void}
 
-Calling \helpref{Delete}{wxthreaddelete} is a graceful way to terminate the
-thread. It asks the thread to terminate and, if the thread code is well
-written, the thread will terminate after the next call to 
-\helpref{TestDestroy}{wxthreadtestdestroy} which should happen quite soon.
+\membersection{wxThread::Delete}\label{wxthreaddelete}
 
-However, if the thread doesn't call \helpref{TestDestroy}{wxthreadtestdestroy} 
-often enough (or at all), the function will not return immediately, but wait
-until the thread terminates. As it may take a long time, and the message processing
-is not stopped during this function execution, message handlers may be
-called from inside it!
+\func{wxThreadError}{Delete}{\void}
 
-Delete() may be called for thread in any state: running, paused or even not yet
-created. Moreover, it must be called if \helpref{Create}{wxthreadcreate} or 
-\helpref{Run}{wxthreadrun} failed for a detached thread to free the memory
-occupied by the thread object. This cleanup will be done in the destructor for joinable
-threads.
+Calling \helpref{Delete}{wxthreaddelete} gracefully terminates a 
+detached thread, either when the thread calls \helpref{TestDestroy}{wxthreadtestdestroy} or finished processing.
 
-Delete() may be called for a thread in any state: running, paused or even not yet created. Moreover,
-it must be called if \helpref{Create}{wxthreadcreate} or \helpref{Run}{wxthreadrun} fail to free
-the memory occupied by the thread object. However, you should not call Delete()
-on a detached thread which already terminated - doing so will probably result
-in a crash because the thread object doesn't exist any more.
+(Note that while this could work on a joinable thread you simply should not
+call this routine on one as afterwards you may not be able to call 
+\helpref{wxThread::Wait}{wxthreadwait} to free the memory of that thread).
 
-For detached threads Delete() will also delete the C++ thread object, but it
-will not do this for joinable ones.
+See \helpref{wxThread deletion}{deletionwxthread} for a broader explanation of this routine.
 
-This function can only be called from another thread context.
+%%FIXME: What does this return and why?
 
 \membersection{wxThread::Entry}\label{wxthreadentry}
 
@@ -134,9 +218,10 @@ be implemented by any derived class. The thread execution will start here.
 The returned value is the thread exit code which is only useful for
 joinable threads and is the value returned by \helpref{Wait}{wxthreadwait}.
 
-This function is called by wxWindows itself and should never be called
+This function is called by wxWidgets itself and should never be called
 directly.
 
+
 \membersection{wxThread::Exit}\label{wxthreadexit}
 
 \func{void}{Exit}{\param{ExitCode }{exitcode = 0}}
@@ -146,9 +231,10 @@ from a derived class. It also can only be called in the context of this
 thread, i.e. a thread can only exit from itself, not from another thread.
 
 This function will terminate the OS thread (i.e. stop the associated path of
-execution) and also delete the associated C++ object for detached threads. 
+execution) and also delete the associated C++ object for detached threads.
 \helpref{wxThread::OnExit}{wxthreadonexit} will be called just before exiting.
 
+
 \membersection{wxThread::GetCPUCount}\label{wxthreadgetcpucount}
 
 \func{static int}{GetCPUCount}{\void}
@@ -159,6 +245,16 @@ Returns the number of system CPUs or -1 if the value is unknown.
 
 \helpref{SetConcurrency}{wxthreadsetconcurrency}
 
+
+\membersection{wxThread::GetCurrentId}\label{wxthreadgetcurrentid}
+
+\func{static unsigned long}{GetCurrentId}{\void}
+
+Returns the platform specific thread ID of the current thread as a
+long.  This can be used to uniquely identify threads, even if they are
+not wxThreads.
+
+
 \membersection{wxThread::GetId}\label{wxthreadgetid}
 
 \constfunc{unsigned long}{GetId}{\void}
@@ -166,6 +262,7 @@ Returns the number of system CPUs or -1 if the value is unknown.
 Gets the thread identifier: this is a platform dependent number that uniquely identifies the
 thread throughout the system during its existence (i.e. the thread identifiers may be reused).
 
+
 \membersection{wxThread::GetPriority}\label{wxthreadgetpriority}
 
 \constfunc{int}{GetPriority}{\void}
@@ -181,35 +278,49 @@ The following priorities are defined:
 \twocolitem{{\bf WXTHREAD\_MAX\_PRIORITY}}{100}
 \end{twocollist}
 
+
 \membersection{wxThread::IsAlive}\label{wxthreadisalive}
 
 \constfunc{bool}{IsAlive}{\void}
 
-Returns TRUE if the thread is alive (i.e. started and not terminating).
+Returns \true if the thread is alive (i.e. started and not terminating).
+
+Note that this function can only safely be used with joinable threads, not
+detached ones as the latter delete themselves and so when the real thread is
+no longer alive, it is not possible to call this function because
+the wxThread object no longer exists.
 
 \membersection{wxThread::IsDetached}\label{wxthreadisdetached}
 
 \constfunc{bool}{IsDetached}{\void}
 
-Returns TRUE if the thread is of the detached kind, FALSE if it is a joinable one.
+Returns \true if the thread is of the detached kind, \false if it is a joinable
+one.
+
 
 \membersection{wxThread::IsMain}\label{wxthreadismain}
 
 \func{static bool}{IsMain}{\void}
 
-Returns TRUE if the calling thread is the main application thread.
+Returns \true if the calling thread is the main application thread.
+
 
 \membersection{wxThread::IsPaused}\label{wxthreadispaused}
 
 \constfunc{bool}{IsPaused}{\void}
 
-Returns TRUE if the thread is paused.
+Returns \true if the thread is paused.
+
 
 \membersection{wxThread::IsRunning}\label{wxthreadisrunning}
 
 \constfunc{bool}{IsRunning}{\void}
 
-Returns TRUE if the thread is running.
+Returns \true if the thread is running.
+
+This method may only be safely used for joinable threads, see the remark in 
+\helpref{IsAlive}{wxthreadisalive}.
+
 
 \membersection{wxThread::Kill}\label{wxthreadkill}
 
@@ -218,7 +329,8 @@ Returns TRUE if the thread is running.
 Immediately terminates the target thread. {\bf This function is dangerous and should
 be used with extreme care (and not used at all whenever possible)!} The resources
 allocated to the thread will not be freed and the state of the C runtime library
-may become inconsistent. Use \helpref{Delete()}{wxthreaddelete} instead.
+may become inconsistent. Use \helpref{Delete()}{wxthreaddelete} for detached 
+threads or \helpref{Wait()}{wxthreadwait} for joinable threads instead.
 
 For detached threads Kill() will also delete the associated C++ object.
 However this will not happen for joinable threads and this means that you will
@@ -230,46 +342,50 @@ This function can only be called from another thread context, i.e. a thread
 cannot kill itself.
 
 It is also an error to call this function for a thread which is not running or
-paused (in the latter case, the thread will be resumed first) - if you do it, 
+paused (in the latter case, the thread will be resumed first) -- if you do it,
 a {\tt wxTHREAD\_NOT\_RUNNING} error will be returned.
 
+
 \membersection{wxThread::OnExit}\label{wxthreadonexit}
 
 \func{void}{OnExit}{\void}
 
 Called when the thread exits. This function is called in the context of the
 thread associated with the wxThread object, not in the context of the main
-thread. This function will not be called if the thread was 
+thread. This function will not be called if the thread was
 \helpref{killed}{wxthreadkill}.
 
 This function should never be called directly.
 
+
 \membersection{wxThread::Pause}\label{wxthreadpause}
 
 \func{wxThreadError}{Pause}{\void}
 
 Suspends the thread. Under some implementations (Win32), the thread is
-suspended immediately, under others it will only be suspended when it calls 
+suspended immediately, under others it will only be suspended when it calls
 \helpref{TestDestroy}{wxthreadtestdestroy} for the next time (hence, if the
 thread doesn't call it at all, it won't be suspended).
 
 This function can only be called from another thread context.
 
+
 \membersection{wxThread::Run}\label{wxthreadrun}
 
 \func{wxThreadError}{Run}{\void}
 
-Starts the thread execution. Should be called after 
+Starts the thread execution. Should be called after
 \helpref{Create}{wxthreadcreate}.
 
 This function can only be called from another thread context.
 
+
 \membersection{wxThread::SetPriority}\label{wxthreadsetpriority}
 
 \func{void}{SetPriority}{\param{int}{ priority}}
 
 Sets the priority of the thread, between $0$ and $100$. It can only be set
-after calling \helpref{Create()}{wxthreadcreate} but before calling 
+after calling \helpref{Create()}{wxthreadcreate} but before calling
 \helpref{Run()}{wxthreadrun}.
 
 The following priorities are already defined:
@@ -281,6 +397,7 @@ The following priorities are already defined:
 \twocolitem{{\bf WXTHREAD\_MAX\_PRIORITY}}{100}
 \end{twocollist}
 
+
 \membersection{wxThread::Sleep}\label{wxthreadsleep}
 
 \func{static void}{Sleep}{\param{unsigned long }{milliseconds}}
@@ -290,6 +407,7 @@ Pauses the thread execution for the given amount of time.
 This function should be used instead of \helpref{wxSleep}{wxsleep} by all worker
 threads (i.e. all except the main one).
 
+
 \membersection{wxThread::Resume}\label{wxthreadresume}
 
 \func{wxThreadError}{Resume}{\void}
@@ -298,6 +416,7 @@ Resumes a thread suspended by the call to \helpref{Pause}{wxthreadpause}.
 
 This function can only be called from another thread context.
 
+
 \membersection{wxThread::SetConcurrency}\label{wxthreadsetconcurrency}
 
 \func{static bool}{SetConcurrency}{\param{size\_t }{level}}
@@ -306,16 +425,22 @@ Sets the thread concurrency level for this process. This is, roughly, the
 number of threads that the system tries to schedule to run in parallel.
 The value of $0$ for {\it level} may be used to set the default one.
 
-Returns TRUE on success or FALSE otherwise (for example, if this function is
-not implemented for this platform - currently everything except Solaris).
+Returns \true on success or false otherwise (for example, if this function is
+not implemented for this platform -- currently everything except Solaris).
+
 
 \membersection{wxThread::TestDestroy}\label{wxthreadtestdestroy}
 
-\func{bool}{TestDestroy}{\void}
+\func{virtual bool}{TestDestroy}{\void}
 
 This function should be called periodically by the thread to ensure that calls
 to \helpref{Pause}{wxthreadpause} and \helpref{Delete}{wxthreaddelete} will
-work. If it returns TRUE, the thread should exit as soon as possible.
+work. If it returns \true, the thread should exit as soon as possible.
+
+Notice that under some platforms (POSIX), implementation of 
+\helpref{Pause}{wxthreadpause} also relies on this function being called, so
+not calling it would prevent both stopping and suspending thread from working.
+
 
 \membersection{wxThread::This}\label{wxthreadthis}
 
@@ -327,6 +452,7 @@ whether the thread is really the main one because NULL may also be returned for
 not created with wxThread class. Generally speaking, the return value for such a thread
 is undefined.
 
+
 \membersection{wxThread::Yield}\label{wxthreadyield}
 
 \func{void}{Yield}{\void}
@@ -334,13 +460,20 @@ is undefined.
 Give the rest of the thread time slice to the system allowing the other threads to run.
 See also \helpref{Sleep()}{wxthreadsleep}.
 
+
 \membersection{wxThread::Wait}\label{wxthreadwait}
 
 \constfunc{ExitCode}{Wait}{\void}
 
-Waits until the thread terminates and returns its exit code or {\tt (ExitCode)-1} on error.
+Waits for a joinable thread to terminate and returns the value the thread
+returned from \helpref{wxThread::Entry}{wxthreadentry} or {\tt (ExitCode)-1} on
+error. Notice that, unlike \helpref{Delete}{wxthreaddelete} doesn't cancel the
+thread in any way so the caller waits for as long as it takes to the thread to
+exit.
 
 You can only Wait() for joinable (not detached) threads.
 
 This function can only be called from another thread context.
 
+See \helpref{wxThread deletion}{deletionwxthread} for a broader explanation of this routine.
+
