/////////////////////////////////////////////////////////////////////////////

// Name:        wx/thread.h

// Purpose:     Thread API

// Author:      Guilhem Lavaux

// Modified by: Vadim Zeitlin (modifications partly inspired by omnithreads

//              package from Olivetti & Oracle Research Laboratory)

// Created:     04/13/98

// Copyright:   (c) Guilhem Lavaux

// Licence:     wxWindows licence

/////////////////////////////////////////////////////////////////////////////

#ifndef _WX_THREAD_H_

#define _WX_THREAD_H_

// ----------------------------------------------------------------------------

// headers

// ----------------------------------------------------------------------------

// get the value of wxUSE_THREADS configuration flag

#include "wx/defs.h"

#if wxUSE_THREADS

// ----------------------------------------------------------------------------

// constants

// ----------------------------------------------------------------------------

enum wxMutexError

{

    wxMUTEX_NO_ERROR = 0,   // operation completed successfully

    wxMUTEX_INVALID,        // mutex hasn't been initialized

    wxMUTEX_DEAD_LOCK,      // mutex is already locked by the calling thread

    wxMUTEX_BUSY,           // mutex is already locked by another thread

    wxMUTEX_UNLOCKED,       // attempt to unlock a mutex which is not locked

    wxMUTEX_TIMEOUT,        // LockTimeout() has timed out

    wxMUTEX_MISC_ERROR      // any other error

};

enum wxCondError

{

    wxCOND_NO_ERROR = 0,

    wxCOND_INVALID,

    wxCOND_TIMEOUT,         // WaitTimeout() has timed out

    wxCOND_MISC_ERROR

};

enum wxSemaError

{

    wxSEMA_NO_ERROR = 0,

    wxSEMA_INVALID,         // semaphore hasn't been initialized successfully

    wxSEMA_BUSY,            // returned by TryWait() if Wait() would block

    wxSEMA_TIMEOUT,         // returned by WaitTimeout()

    wxSEMA_OVERFLOW,        // Post() would increase counter past the max

    wxSEMA_MISC_ERROR

};

enum wxThreadError

{

    wxTHREAD_NO_ERROR = 0,      // No error

    wxTHREAD_NO_RESOURCE,       // No resource left to create a new thread

    wxTHREAD_RUNNING,           // The thread is already running

    wxTHREAD_NOT_RUNNING,       // The thread isn't running

    wxTHREAD_KILLED,            // Thread we waited for had to be killed

    wxTHREAD_MISC_ERROR         // Some other error

};

enum wxThreadKind

{

    wxTHREAD_DETACHED,

    wxTHREAD_JOINABLE

};

enum wxThreadWait

{

    wxTHREAD_WAIT_BLOCK,

    wxTHREAD_WAIT_YIELD,       // process events while waiting; MSW only

    wxTHREAD_WAIT_DEFAULT = wxTHREAD_WAIT_BLOCK

};

// Obsolete synonyms for wxPRIORITY_XXX for backwards compatibility-only

enum

{

    WXTHREAD_MIN_PRIORITY      = wxPRIORITY_MIN,

    WXTHREAD_DEFAULT_PRIORITY  = wxPRIORITY_DEFAULT,

    WXTHREAD_MAX_PRIORITY      = wxPRIORITY_MAX

};

// There are 2 types of mutexes: normal mutexes and recursive ones. The attempt

// to lock a normal mutex by a thread which already owns it results in

// undefined behaviour (it always works under Windows, it will almost always

// result in a deadlock under Unix). Locking a recursive mutex in such

// situation always succeeds and it must be unlocked as many times as it has

// been locked.

//

// However recursive mutexes have several important drawbacks: first, in the

// POSIX implementation, they're less efficient. Second, and more importantly,

// they CANNOT BE USED WITH CONDITION VARIABLES under Unix! Using them with

// wxCondition will work under Windows and some Unices (notably Linux) but will

// deadlock under other Unix versions (e.g. Solaris). As it might be difficult

// to ensure that a recursive mutex is not used with wxCondition, it is a good

// idea to avoid using recursive mutexes at all. Also, the last problem with

// them is that some (older) Unix versions don't support this at all -- which

// results in a configure warning when building and a deadlock when using them.

enum wxMutexType

{

    // normal mutex: try to always use this one

    wxMUTEX_DEFAULT,

    // recursive mutex: don't use these ones with wxCondition

    wxMUTEX_RECURSIVE

};

// forward declarations

class WXDLLIMPEXP_FWD_BASE wxThreadHelper;

class WXDLLIMPEXP_FWD_BASE wxConditionInternal;

class WXDLLIMPEXP_FWD_BASE wxMutexInternal;

class WXDLLIMPEXP_FWD_BASE wxSemaphoreInternal;

class WXDLLIMPEXP_FWD_BASE wxThreadInternal;

// ----------------------------------------------------------------------------

// A mutex object is a synchronization object whose state is set to signaled

// when it is not owned by any thread, and nonsignaled when it is owned. Its

// name comes from its usefulness in coordinating mutually-exclusive access to

// a shared resource. Only one thread at a time can own a mutex object.

// ----------------------------------------------------------------------------

// you should consider wxMutexLocker whenever possible instead of directly

// working with wxMutex class - it is safer

class WXDLLIMPEXP_BASE wxMutex

{

public:

    // constructor & destructor

    // ------------------------

    // create either default (always safe) or recursive mutex

    wxMutex(wxMutexType mutexType = wxMUTEX_DEFAULT);

    // destroys the mutex kernel object

    ~wxMutex();

    // test if the mutex has been created successfully

    bool IsOk() const;

    // mutex operations

    // ----------------

    // Lock the mutex, blocking on it until it is unlocked by the other thread.

    // The result of locking a mutex already locked by the current thread

    // depend on the mutex type.

    //

    // The caller must call Unlock() later if Lock() returned wxMUTEX_NO_ERROR.

    wxMutexError Lock();

    // Same as Lock() but return wxMUTEX_TIMEOUT if the mutex can't be locked

    // during the given number of milliseconds

    wxMutexError LockTimeout(unsigned long ms);

    // Try to lock the mutex: if it is currently locked, return immediately

    // with an error. Otherwise the caller must call Unlock().

    wxMutexError TryLock();

    // Unlock the mutex. It is an error to unlock an already unlocked mutex

    wxMutexError Unlock();

protected:

    wxMutexInternal *m_internal;

    friend class wxConditionInternal;

    wxDECLARE_NO_COPY_CLASS(wxMutex);

};

// a helper class which locks the mutex in the ctor and unlocks it in the dtor:

// this ensures that mutex is always unlocked, even if the function returns or

// throws an exception before it reaches the end

class WXDLLIMPEXP_BASE wxMutexLocker

{

public:

    // lock the mutex in the ctor

    wxMutexLocker(wxMutex& mutex)

        : m_isOk(false), m_mutex(mutex)

        { m_isOk = ( m_mutex.Lock() == wxMUTEX_NO_ERROR ); }

    // returns true if mutex was successfully locked in ctor

    bool IsOk() const

        { return m_isOk; }

    // unlock the mutex in dtor

    ~wxMutexLocker()

        { if ( IsOk() ) m_mutex.Unlock(); }

private:

    // no assignment operator nor copy ctor

    wxMutexLocker(const wxMutexLocker&);

    wxMutexLocker& operator=(const wxMutexLocker&);

    bool     m_isOk;

    wxMutex& m_mutex;

};

// ----------------------------------------------------------------------------

// Critical section: this is the same as mutex but is only visible to the

// threads of the same process. For the platforms which don't have native

// support for critical sections, they're implemented entirely in terms of

// mutexes.

//

// NB: wxCriticalSection object does not allocate any memory in its ctor

//     which makes it possible to have static globals of this class

// ----------------------------------------------------------------------------

// in order to avoid any overhead under platforms where critical sections are

// just mutexes make all wxCriticalSection class functions inline

#if !defined(__WINDOWS__)

    #define wxCRITSECT_IS_MUTEX 1

    #define wxCRITSECT_INLINE WXEXPORT inline

#else // MSW

    #define wxCRITSECT_IS_MUTEX 0

    #define wxCRITSECT_INLINE

#endif // MSW/!MSW

enum wxCriticalSectionType

{

    // recursive critical section

    wxCRITSEC_DEFAULT,

    // non-recursive critical section

    wxCRITSEC_NON_RECURSIVE

};

// you should consider wxCriticalSectionLocker whenever possible instead of

// directly working with wxCriticalSection class - it is safer

class WXDLLIMPEXP_BASE wxCriticalSection

{

public:

    // ctor & dtor

    wxCRITSECT_INLINE wxCriticalSection( wxCriticalSectionType critSecType = wxCRITSEC_DEFAULT );

    wxCRITSECT_INLINE ~wxCriticalSection();

    // enter the section (the same as locking a mutex)

    wxCRITSECT_INLINE void Enter();

    // try to enter the section (the same as trying to lock a mutex)

    wxCRITSECT_INLINE bool TryEnter();

    // leave the critical section (same as unlocking a mutex)

    wxCRITSECT_INLINE void Leave();

private:

#if wxCRITSECT_IS_MUTEX

    wxMutex m_mutex;

#elif defined(__WINDOWS__)

    // we can't allocate any memory in the ctor, so use placement new -

    // unfortunately, we have to hardcode the sizeof() here because we can't

    // include windows.h from this public header and we also have to use the

    // union to force the correct (i.e. maximal) alignment

    //

    // if CRITICAL_SECTION size changes in Windows, you'll get an assert from

    // thread.cpp and will need to increase the buffer size

#ifdef __WIN64__

    typedef char wxCritSectBuffer[40];

#else // __WIN32__

    typedef char wxCritSectBuffer[24];

#endif

    union

    {

        unsigned long m_dummy1;

        void *m_dummy2;

        wxCritSectBuffer m_buffer;

    };

#endif // Unix/Win32

    wxDECLARE_NO_COPY_CLASS(wxCriticalSection);

};

#if wxCRITSECT_IS_MUTEX

    // implement wxCriticalSection using mutexes

    inline wxCriticalSection::wxCriticalSection( wxCriticalSectionType critSecType )

       : m_mutex( critSecType == wxCRITSEC_DEFAULT ? wxMUTEX_RECURSIVE : wxMUTEX_DEFAULT )  { }

    inline wxCriticalSection::~wxCriticalSection() { }

    inline void wxCriticalSection::Enter() { (void)m_mutex.Lock(); }

    inline bool wxCriticalSection::TryEnter() { return m_mutex.TryLock() == wxMUTEX_NO_ERROR; }

    inline void wxCriticalSection::Leave() { (void)m_mutex.Unlock(); }

#endif // wxCRITSECT_IS_MUTEX

#undef wxCRITSECT_INLINE

#undef wxCRITSECT_IS_MUTEX

// wxCriticalSectionLocker is the same to critical sections as wxMutexLocker is

// to mutexes

class WXDLLIMPEXP_BASE wxCriticalSectionLocker

{

public:

    wxCriticalSectionLocker(wxCriticalSection& cs)

        : m_critsect(cs)

    {

        m_critsect.Enter();

    }

    ~wxCriticalSectionLocker()

    {

        m_critsect.Leave();

    }

private:

    wxCriticalSection& m_critsect;

    wxDECLARE_NO_COPY_CLASS(wxCriticalSectionLocker);

};

// ----------------------------------------------------------------------------

// wxCondition models a POSIX condition variable which allows one (or more)

// thread(s) to wait until some condition is fulfilled

// ----------------------------------------------------------------------------

class WXDLLIMPEXP_BASE wxCondition

{

public:

    // Each wxCondition object is associated with a (single) wxMutex object.

    // The mutex object MUST be locked before calling Wait()

    wxCondition(wxMutex& mutex);

    // dtor is not virtual, don't use this class polymorphically

    ~wxCondition();

    // return true if the condition has been created successfully

    bool IsOk() const;

    // NB: the associated mutex MUST be locked beforehand by the calling thread

    //

    // it atomically releases the lock on the associated mutex

    // and starts waiting to be woken up by a Signal()/Broadcast()

    // once its signaled, then it will wait until it can reacquire

    // the lock on the associated mutex object, before returning.

    wxCondError Wait();

    // std::condition_variable-like variant that evaluates the associated condition

    template<typename Functor>

    wxCondError Wait(const Functor& predicate)

    {

        while ( !predicate() )

        {

            wxCondError e = Wait();

            if ( e != wxCOND_NO_ERROR )

                return e;

        }

        return wxCOND_NO_ERROR;

    }

    // exactly as Wait() except that it may also return if the specified

    // timeout elapses even if the condition hasn't been signalled: in this

    // case, the return value is wxCOND_TIMEOUT, otherwise (i.e. in case of a

    // normal return) it is wxCOND_NO_ERROR.

    //

    // the timeout parameter specifies an interval that needs to be waited for

    // in milliseconds

    wxCondError WaitTimeout(unsigned long milliseconds);

    // NB: the associated mutex may or may not be locked by the calling thread

    //

    // this method unblocks one thread if any are blocking on the condition.

    // if no thread is blocking in Wait(), then the signal is NOT remembered

    // The thread which was blocking on Wait() will then reacquire the lock

    // on the associated mutex object before returning

    wxCondError Signal();

    // NB: the associated mutex may or may not be locked by the calling thread

    //

    // this method unblocks all threads if any are blocking on the condition.

    // if no thread is blocking in Wait(), then the signal is NOT remembered

    // The threads which were blocking on Wait() will then reacquire the lock

    // on the associated mutex object before returning.

    wxCondError Broadcast();

private:

    wxConditionInternal *m_internal;

    wxDECLARE_NO_COPY_CLASS(wxCondition);

};

// ----------------------------------------------------------------------------

// wxSemaphore: a counter limiting the number of threads concurrently accessing

//              a shared resource

// ----------------------------------------------------------------------------

class WXDLLIMPEXP_BASE wxSemaphore

{

public:

    // specifying a maxcount of 0 actually makes wxSemaphore behave as if there

    // is no upper limit, if maxcount is 1 the semaphore behaves as a mutex

    wxSemaphore( int initialcount = 0, int maxcount = 0 );

    // dtor is not virtual, don't use this class polymorphically

    ~wxSemaphore();

    // return true if the semaphore has been created successfully

    bool IsOk() const;

    // wait indefinitely, until the semaphore count goes beyond 0

    // and then decrement it and return (this method might have been called

    // Acquire())

    wxSemaError Wait();

    // same as Wait(), but does not block, returns wxSEMA_NO_ERROR if

    // successful and wxSEMA_BUSY if the count is currently zero

    wxSemaError TryWait();

    // same as Wait(), but as a timeout limit, returns wxSEMA_NO_ERROR if the

    // semaphore was acquired and wxSEMA_TIMEOUT if the timeout has elapsed

    wxSemaError WaitTimeout(unsigned long milliseconds);

    // increments the semaphore count and signals one of the waiting threads

    wxSemaError Post();

private:

    wxSemaphoreInternal *m_internal;

    wxDECLARE_NO_COPY_CLASS(wxSemaphore);

};

// ----------------------------------------------------------------------------

// wxThread: class encapsulating a thread of execution

// ----------------------------------------------------------------------------

// there are two different kinds of threads: joinable and detached (default)

// ones. Only joinable threads can return a return code and only detached

// threads auto-delete themselves - the user should delete the joinable

// threads manually.

// NB: in the function descriptions the words "this thread" mean the thread

//     created by the wxThread object while "main thread" is the thread created

//     during the process initialization (a.k.a. the GUI thread)

// On VMS thread pointers are 64 bits (also needed for other systems???

#ifdef __VMS

   typedef unsigned long long wxThreadIdType;

#else

   typedef unsigned long wxThreadIdType;

#endif

class WXDLLIMPEXP_BASE wxThread

{

public:

    // the return type for the thread function

    typedef void *ExitCode;

    // static functions

        // Returns the wxThread object for the calling thread. nullptr is returned

        // if the caller is the main thread (but it's recommended to use

        // IsMain() and only call This() for threads other than the main one

        // because nullptr is also returned on error). If the thread wasn't

        // created with wxThread class, the returned value is undefined.

    static wxThread *This();

        // Returns true if current thread is the main thread.

        //

        // Notice that it also returns true if main thread id hadn't been

        // initialized yet on the assumption that it's too early in wx startup

        // process for any other threads to have been created in this case.

    static bool IsMain()

    {

        return !ms_idMainThread || GetCurrentId() == ms_idMainThread;

    }

        // Return the main thread id

    static wxThreadIdType GetMainId() { return ms_idMainThread; }

        // Release the rest of our time slice letting the other threads run

    static void Yield();

        // Sleep during the specified period of time in milliseconds

        //

        // This is the same as wxMilliSleep().

    static void Sleep(unsigned long milliseconds);

        // get the number of system CPUs - useful with SetConcurrency()

        // (the "best" value for it is usually number of CPUs + 1)

        //

        // Returns -1 if unknown, number of CPUs otherwise

    static int GetCPUCount();

        // Get the platform specific thread ID and return as a long.  This

        // can be used to uniquely identify threads, even if they are not

        // wxThreads.  This is used by wxPython.

    static wxThreadIdType GetCurrentId();

        // sets the concurrency level: this is, roughly, the number of threads

        // the system tries to schedule to run in parallel. 0 means the

        // default value (usually acceptable, but may not yield the best

        // performance for this process)

        //

        // Returns true on success, false otherwise (if not implemented, for

        // example)

    static bool SetConcurrency(size_t level);

    // constructor only creates the C++ thread object and doesn't create (or

    // start) the real thread

    wxThread(wxThreadKind kind = wxTHREAD_DETACHED);

    // functions that change the thread state: all these can only be called

    // from _another_ thread (typically the thread that created this one, e.g.

    // the main thread), not from the thread itself

        // create a new thread and optionally set the stack size on

        // platforms that support that - call Run() to start it

    wxThreadError Create(unsigned int stackSize = 0);

        // starts execution of the thread - from the moment Run() is called

        // the execution of wxThread::Entry() may start at any moment, caller

        // shouldn't suppose that it starts after (or before) Run() returns.

    wxThreadError Run();

        // stops the thread if it's running and deletes the wxThread object if

        // this is a detached thread freeing its memory - otherwise (for

        // joinable threads) you still need to delete wxThread object

        // yourself.

        //

        // this function only works if the thread calls TestDestroy()

        // periodically - the thread will only be deleted the next time it

        // does it!

        //

        // will fill the rc pointer with the thread exit code if it's non-null

    wxThreadError Delete(ExitCode *rc = nullptr,

                         wxThreadWait waitMode = wxTHREAD_WAIT_DEFAULT);

        // waits for a joinable thread to finish and returns its exit code

        //

        // Returns (ExitCode)-1 on error (for example, if the thread is not

        // joinable)

    ExitCode Wait(wxThreadWait waitMode = wxTHREAD_WAIT_DEFAULT);

        // kills the thread without giving it any chance to clean up - should

        // not be used under normal circumstances, use Delete() instead.

        // It is a dangerous function that should only be used in the most

        // extreme cases!

        //

        // The wxThread object is deleted by Kill() if the thread is

        // detachable, but you still have to delete it manually for joinable

        // threads.

    wxThreadError Kill();

        // pause a running thread: as Delete(), this only works if the thread

        // calls TestDestroy() regularly

    wxThreadError Pause();

        // resume a paused thread

    wxThreadError Resume();

    // priority

        // Sets the priority to "prio" which must be in 0..100 range (see

        // also wxPRIORITY_XXX constants).

    void SetPriority(unsigned int prio);

        // Get the current priority.

    unsigned int GetPriority() const;

    // thread status inquiries

        // Returns true if the thread is alive: i.e. running or suspended

    bool IsAlive() const;

        // Returns true if the thread is running (not paused, not killed).

    bool IsRunning() const;

        // Returns true if the thread is suspended

    bool IsPaused() const;

        // is the thread of detached kind?

    bool IsDetached() const { return m_isDetached; }

    // Get the thread ID - a platform dependent number which uniquely

    // identifies a thread inside a process

    wxThreadIdType GetId() const;

#ifdef __WINDOWS__

    // Get the internal OS handle

    WXHANDLE MSWGetHandle() const;

#endif // __WINDOWS__

    wxThreadKind GetKind() const

        { return m_isDetached ? wxTHREAD_DETACHED : wxTHREAD_JOINABLE; }

    // Returns true if the thread was asked to terminate: this function should

    // be called by the thread from time to time, otherwise the main thread

    // will be left forever in Delete()!

    virtual bool TestDestroy();

    // dtor is public, but the detached threads should never be deleted - use

    // Delete() instead (or leave the thread terminate by itself)

    virtual ~wxThread();

    // sets name to assist debugging

    static bool SetNameForCurrent(const wxString &name);

protected:

    // sets name to assist debugging

    bool SetName(const wxString &name);

    // exits from the current thread - can be called only from this thread

    void Exit(ExitCode exitcode = nullptr);

    // entry point for the thread - called by Run() and executes in the context

    // of this thread.

    virtual void *Entry() = 0;

    // Callbacks which may be overridden by the derived class to perform some

    // specific actions when the thread is deleted or killed. By default they

    // do nothing.

    // This one is called by Delete() before actually deleting the thread and

    // is executed in the context of the thread that called Delete().

    virtual void OnDelete() {}

    // This one is called by Kill() before killing the thread and is executed

    // in the context of the thread that called Kill().

    virtual void OnKill() {}

    // called when the thread exits - in the context of this thread

    //

    // NB: this function will not be called if the thread is Kill()ed

    virtual void OnExit() {}

private:

    // no copy ctor/assignment operator

    wxThread(const wxThread&);

    wxThread& operator=(const wxThread&);

    friend class wxThreadInternal;

    friend class wxThreadModule;

    // the main thread identifier, should be set on startup

    static wxThreadIdType ms_idMainThread;

    // the (platform-dependent) thread class implementation

    wxThreadInternal *m_internal;

    // protects access to any methods of wxThreadInternal object

    mutable wxCriticalSection m_critsect;

    // true if the thread is detached, false if it is joinable

    bool m_isDetached;

};

// wxThreadHelperThread class

// --------------------------

class wxThreadHelperThread : public wxThread

{

public:

    // constructor only creates the C++ thread object and doesn't create (or

    // start) the real thread

    wxThreadHelperThread(wxThreadHelper& owner, wxThreadKind kind)

        : wxThread(kind), m_owner(owner)

        { }

protected:

    // entry point for the thread -- calls Entry() in owner.

    virtual void *Entry() override;

private:

    // the owner of the thread

    wxThreadHelper& m_owner;

    // no copy ctor/assignment operator

    wxThreadHelperThread(const wxThreadHelperThread&);

    wxThreadHelperThread& operator=(const wxThreadHelperThread&);

};

// ----------------------------------------------------------------------------

// wxThreadHelper: this class implements the threading logic to run a

// background task in another object (such as a window).  It is a mix-in: just

// derive from it to implement a threading background task in your class.

// ----------------------------------------------------------------------------

class wxThreadHelper

{

private:

    void KillThread()

    {

        // If wxThreadHelperThread is detached and is about to finish, it will

        // set m_thread to nullptr so don't delete it then.

        // But if KillThread is called before wxThreadHelperThread (in detached mode)

        // sets it to nullptr, then the thread object still exists and can be killed

        wxCriticalSectionLocker locker(m_critSection);

        if ( m_thread )

        {

            m_thread->Kill();

            if ( m_kind == wxTHREAD_JOINABLE )

              delete m_thread;

            m_thread = nullptr;

        }

    }

public:

    // constructor only initializes m_thread to nullptr

    wxThreadHelper(wxThreadKind kind = wxTHREAD_JOINABLE)

        : m_thread(nullptr), m_kind(kind) { }

    // destructor deletes m_thread

    virtual ~wxThreadHelper() { KillThread(); }

    // create a new thread (and optionally set the stack size on platforms that

    // support/need that), call Run() to start it

    wxThreadError CreateThread(wxThreadKind kind = wxTHREAD_JOINABLE,

                               unsigned int stackSize = 0)

    {

        KillThread();

        m_kind = kind;

        m_thread = new wxThreadHelperThread(*this, m_kind);

        return m_thread->Create(stackSize);

    }

    // entry point for the thread - called by Run() and executes in the context

    // of this thread.

    virtual void *Entry() = 0;

    // returns a pointer to the thread which can be used to call Run()

    wxThread *GetThread() const

    {

        wxCriticalSectionLocker locker(m_critSection);

        wxThread* thread = m_thread;

        return thread;

    }

protected:

    wxThread *m_thread;

    wxThreadKind m_kind;

    mutable wxCriticalSection m_critSection; // To guard the m_thread variable

    friend class wxThreadHelperThread;

};

// call Entry() in owner, put it down here to avoid circular declarations

inline void *wxThreadHelperThread::Entry()

{

    void * const result = m_owner.Entry();

    wxCriticalSectionLocker locker(m_owner.m_critSection);

    // Detached thread will be deleted after returning, so make sure

    // wxThreadHelper::GetThread will not return an invalid pointer.

    // And that wxThreadHelper::KillThread will not try to kill

    // an already deleted thread

    if ( m_owner.m_kind == wxTHREAD_DETACHED )

        m_owner.m_thread = nullptr;

    return result;

}

// ----------------------------------------------------------------------------

// Automatic initialization

// ----------------------------------------------------------------------------

// GUI mutex handling.

void WXDLLIMPEXP_BASE wxMutexGuiEnter();

void WXDLLIMPEXP_BASE wxMutexGuiLeave();

// macros for entering/leaving critical sections which may be used without

// having to take them inside "#if wxUSE_THREADS"

#define wxENTER_CRIT_SECT(cs)   (cs).Enter()

#define wxLEAVE_CRIT_SECT(cs)   (cs).Leave()

#define wxCRIT_SECT_DECLARE(cs) static wxCriticalSection cs

#define wxCRIT_SECT_DECLARE_MEMBER(cs) wxCriticalSection cs

#define wxCRIT_SECT_LOCKER(name, cs)  wxCriticalSectionLocker name(cs)

// function for checking if we're in the main thread which may be used whether

// wxUSE_THREADS is 0 or 1

inline bool wxIsMainThread() { return wxThread::IsMain(); }

#else // !wxUSE_THREADS

// no thread support

inline void wxMutexGuiEnter() { }

inline void wxMutexGuiLeave() { }

// macros for entering/leaving critical sections which may be used without

// having to take them inside "#if wxUSE_THREADS"

// (the implementation uses dummy structs to force semicolon after the macro)

#define wxENTER_CRIT_SECT(cs)            do {} while (0)

#define wxLEAVE_CRIT_SECT(cs)            do {} while (0)

#define wxCRIT_SECT_DECLARE(cs)          struct wxDummyCS##cs

#define wxCRIT_SECT_DECLARE_MEMBER(cs)   struct wxDummyCSMember##cs { }

#define wxCRIT_SECT_LOCKER(name, cs)     struct wxDummyCSLocker##name

// if there is only one thread, it is always the main one

inline bool wxIsMainThread() { return true; }

#endif // wxUSE_THREADS/!wxUSE_THREADS

// mark part of code as being a critical section: this macro declares a

// critical section with the given name and enters it immediately and leaves

// it at the end of the current scope

//

// example:

//

//      int Count()

//      {

//          static int s_counter = 0;

//

//          wxCRITICAL_SECTION(counter);

//

//          return ++s_counter;

//      }

//

// this function is MT-safe in presence of the threads but there is no

// overhead when the library is compiled without threads

#define wxCRITICAL_SECTION(name) \

    wxCRIT_SECT_DECLARE(s_cs##name);  \

    wxCRIT_SECT_LOCKER(cs##name##Locker, s_cs##name)

// automatically lock GUI mutex in ctor and unlock it in dtor

class WXDLLIMPEXP_BASE wxMutexGuiLocker

{

public:

    wxMutexGuiLocker() { wxMutexGuiEnter(); }

   ~wxMutexGuiLocker() { wxMutexGuiLeave(); }

};

// -----------------------------------------------------------------------------

// implementation only until the end of file

// -----------------------------------------------------------------------------

#if wxUSE_THREADS

#if defined(__WINDOWS__) || defined(__DARWIN__)

    // unlock GUI if there are threads waiting for and lock it back when

    // there are no more of them - should be called periodically by the main

    // thread

    extern void WXDLLIMPEXP_BASE wxMutexGuiLeaveOrEnter();

    // returns true if the main thread has GUI lock

    extern bool WXDLLIMPEXP_BASE wxGuiOwnedByMainThread();

    // wakes up the main thread if it's sleeping inside ::GetMessage()

    extern void WXDLLIMPEXP_BASE wxWakeUpMainThread();

#ifndef __DARWIN__

    // return true if the main thread is waiting for some other to terminate:

    // wxApp then should block all "dangerous" messages

    extern bool WXDLLIMPEXP_BASE wxIsWaitingForThread();

#endif

#endif // MSW, OSX

#endif // wxUSE_THREADS

#endif // _WX_THREAD_H_