docs/latex/wx/thread.tex

   1 \section{\class{wxThread}}\label{wxthread}
   2
   3 A thread is basically a path of execution through a program. Threads are also
   4 sometimes called {\it light-weight processes}, but the fundamental difference
   5 between threads and processes is that memory spaces of different processes are
   6 separated while all threads share the same address space. While it makes it
   7 much easier to share common data between several threads, it also makes much
   8 easier to shoot oneself in the foot, so careful use of synchronization objects
   9 such as \helpref{mutexes}{wxmutex} and/or \helpref{critical sections}{wxcriticalsection} is recommended.
  10
  11 There are two types of threads in wxWindows: {\it detached} and {\it joinable}
  12 ones, just as in POSIX thread API (but unlike Win32 threads where all threads
  13 are joinable). The difference between the two is that only joinbale threads
  14 can return a return code - it is returned by Wait() function. The detached
  15 threads (default) can not be waited for.
  16
  17 You shouldn't hurry to create all the threads joinable, however, because this
  18 has a disadvantage as well: you {\bf must} Wait() for a joinable thread of the
  19 system resources used by it will never be freed and you also must delete the
  20 corresponding wxThread object yourself, while detached threads are of the
  21 "fire-and-forget" kind: you only have to start a detached thread and it will
  22 terminate and destroy itself.
  23
  24 This means, of course, that all detached threads {\bf must} be created on the
  25 heap because the thread will call {\tt delete this;} upon termination. The
  26 joinable threads may be created on stack (don't create global thread objects
  27 because they allocate memory in their constructor which is a badthing to do),
  28 although usually they will be created on the heap as well.
  29
  30 \wxheading{Derived from}
  31
  32 None.
  33
  34 \wxheading{Include files}
  35
  36 <wx/thread.h>
  37
  38 \wxheading{See also}
  39
  40 \helpref{wxMutex}{wxmutex}, \helpref{wxCondition}{wxcondition}, \helpref{wxCriticalSection}{wxcriticalsection}
  41
  42 \latexignore{\rtfignore{\wxheading{Members}}}
  43
  44 \membersection{wxThread::wxThread}\label{wxthreadctor}
  45
  46 \func{}{wxThread}{\void}
  47
  48 Constructor creates a new detached (default) or joinable C++ thread object. It
  49 does not create (or starts execution of) the real thread - for this you should
  50 use \helpref{Create}{wxthreadcreate} and \helpref{Run}{wxthreadrun} methods.
  51
  52 \membersection{wxThread::\destruct{wxThread}}
  53
  54 \func{}{\destruct{wxThread}}{\void}
  55
  56 Destructor frees the ressources associated with the thread. Notice that you
  57 should never delete a detached thread - you may only call
  58 \helpref{Delete}{wxthreaddelete} on it or wait until it terminates (and auto
  59 destructs) itself. Because the detached threads delete themselves, they can
  60 only be allocated on the heap.
  61
  62 The joinable threads, however, may and should be deleted explicitly and
  63 \helpref{Delete}{wxthreaddelete} and \helpref{Kill}{wxthreadkill} functions
  64 will not delete the C++ thread object. It is also safe to allocate them on
  65 stack.
  66
  67 \membersection{wxThread::Create}\label{wxthreadcreate}
  68
  69 \func{wxThreadError}{Create}{\void}
  70
  71 Creates a new thread. The thread object is created in the suspended state, you
  72 should call \helpref{Run}{wxthreadrun} to start running it.
  73
  74 \wxheading{Return value}
  75
  76 One of:
  77
  78 \twocolwidtha{7cm}
  79 \begin{twocollist}\itemsep=0pt
  80 \twocolitem{{\bf wxTHREAD\_NO\_ERROR}}{There was no error.}
  81 \twocolitem{{\bf wxTHREAD\_NO\_RESOURCE}}{There were insufficient resources to create a new thread.}
  82 \twocolitem{{\bf wxTHREAD\_RUNNING}}{The thread is already running.}
  83 \end{twocollist}
  84
  85 \membersection{wxThread::Delete}\label{wxthreaddelete}
  86
  87 \func{void}{Delete}{\void}
  88
  89 Calling \helpref{Delete}{wxthreaddelete} is a graceful way to terminate the
  90 thread. It asks the thread to terminate and, if the thread code is well
  91 written, the thread will terminate after the next call to
  92 \helpref{TestDestroy}{wxthreadtestdestroy} which should happen quiet soon.
  93
  94 However, if the thread doesn't call \helpref{TestDestroy}{wxthreadtestdestroy}
  95 often enough (or at all), the function will not return immediately, but wait
  96 until the thread terminates. As it may take a long time, the message processing
  97 is not stopped during this function execution, so the message handlers may be
  98 called from inside it!
  99
 100 Delete() may be called for thread in any state: running, paused or even not yet
 101 created. Moreover, it must be called if \helpref{Create}{wxthreadcreate} or
 102 \helpref{Run}{wxthreadrun} failed for a detached thread to free the memory
 103 occupied by the thread object (it will be done in the destructor for joinable
 104 threads).
 105
 106 Delete() may be called for thread in any state: running, paused or even not yet created. Moreover,
 107 it must be called if \helpref{Create}{wxthreadcreate} or \helpref{Run}{wxthreadrun} fail to free
 108 the memory occupied by the thread object. However, you should not call Delete()
 109 on a detached thread which already terminated - doing so will probably result
 110 in a crash because the thread object doesn't exist any more.
 111
 112 For detached threads Delete() will also delete the C++ thread object, but it
 113 will not do this for joinable ones.
 114
 115 This function can only be called from another thread context.
 116
 117 \membersection{wxThread::Entry}\label{wxthreadentry}
 118
 119 \func{virtual ExitCode}{Entry}{\void}
 120
 121 This is the entry point of the thread. This function is pure virtual and must
 122 be implemented by any derived class. The thread execution will start here.
 123
 124 The returned value is the thread exit code which is only useful for the
 125 joinable threads and is the value returned by \helpref{Wait}{wxthreadwait}.
 126
 127 This function is called by wxWindows itself and should never be called
 128 directly.
 129
 130 \membersection{wxThread::GetId}\label{wxthreadgetid}
 131
 132 \constfunc{unsigned long}{GetId}{\void}
 133
 134 Gets the thread identifier: this is a platform dependent number which uniquely identifies the
 135 thread throughout the system during its existence (i.e. the thread identifiers may be reused).
 136
 137 \membersection{wxThread::GetPriority}\label{wxthreadgetpriority}
 138
 139 \constfunc{int}{GetPriority}{\void}
 140
 141 Gets the priority of the thread, between zero and 100.
 142
 143 The following priorities are defined:
 144
 145 \twocolwidtha{7cm}
 146 \begin{twocollist}\itemsep=0pt
 147 \twocolitem{{\bf WXTHREAD\_MIN\_PRIORITY}}{0}
 148 \twocolitem{{\bf WXTHREAD\_DEFAULT\_PRIORITY}}{50}
 149 \twocolitem{{\bf WXTHREAD\_MAX\_PRIORITY}}{100}
 150 \end{twocollist}
 151
 152 \membersection{wxThread::IsAlive}\label{wxthreadisalive}
 153
 154 \constfunc{bool}{IsAlive}{\void}
 155
 156 Returns TRUE if the thread is alive (i.e. started and not terminating).
 157
 158 \membersection{wxThread::IsDetached}\label{wxthreadisdetached}
 159
 160 \constfunc{bool}{IsDetached}{\void}
 161
 162 Returns TRUE if the thread is of detached kind, FALSE if it is a joinable one.
 163
 164 \membersection{wxThread::IsMain}\label{wxthreadismain}
 165
 166 \func{static bool}{IsMain}{\void}
 167
 168 Returns TRUE if the calling thread is the main application thread.
 169
 170 \membersection{wxThread::IsPaused}\label{wxthreadispaused}
 171
 172 \constfunc{bool}{IsPaused}{\void}
 173
 174 Returns TRUE if the thread is paused.
 175
 176 \membersection{wxThread::IsRunning}\label{wxthreadisrunning}
 177
 178 \constfunc{bool}{IsRunning}{\void}
 179
 180 Returns TRUE if the thread is running.
 181
 182 \membersection{wxThread::Kill}\label{wxthreadkill}
 183
 184 \func{wxThreadError}{Kill}{\void}
 185
 186 Immediately terminates the target thread. {\bf This function is dangerous and should
 187 be used with extreme care (and not used at all whenever possible)!} The resources
 188 allocated to the thread will not be freed and the state of the C runtime library
 189 may become inconsistent. Use \helpref{Delete()}{wxthreaddelete} instead.
 190
 191 For detached threads Kill() will also delete the associated C++ object.
 192
 193 This function can only be called from another thread context.
 194
 195 \membersection{wxThread::OnExit}\label{wxthreadonexit}
 196
 197 \func{void}{OnExit}{\void}
 198
 199 Called when the thread exits. This function is called in the context of the thread
 200 associated with the wxThread object, not in the context of the main thread.
 201
 202 This function should never be called directly.
 203
 204 \membersection{wxThread::Pause}\label{wxthreadpause}
 205
 206 \func{wxThreadError}{Pause}{\void}
 207
 208 Suspends the thread. Under some implementations (Win32), the thread is
 209 suspended immediately, under others it will only be suspended when it calls
 210 \helpref{TestDestroy}{wxthreadtestdestroy} for the next time (hence, if the
 211 thread doesn't call it at all, it won't be suspended).
 212
 213 This function can only be called from another thread context.
 214
 215 \membersection{wxThread::Run}\label{wxthreadrun}
 216
 217 \func{wxThreadError}{Run}{\void}
 218
 219 Starts the thread execution. Should be called after
 220 \helpref{Create}{wxthreadcreate}.
 221
 222 This function can only be called from another thread context.
 223
 224 \membersection{wxThread::SetPriority}\label{wxthreadsetpriority}
 225
 226 \func{void}{SetPriority}{\param{int}{ priority}}
 227
 228 Sets the priority of the thread, between zero and 100. This must be set before the thread is created.
 229
 230 The following priorities are already defined:
 231
 232 \twocolwidtha{7cm}
 233 \begin{twocollist}\itemsep=0pt
 234 \twocolitem{{\bf WXTHREAD\_MIN\_PRIORITY}}{0}
 235 \twocolitem{{\bf WXTHREAD\_DEFAULT\_PRIORITY}}{50}
 236 \twocolitem{{\bf WXTHREAD\_MAX\_PRIORITY}}{100}
 237 \end{twocollist}
 238
 239 \membersection{wxThread::Sleep}\label{wxthreadsleep}
 240
 241 \func{static void}{Sleep}{\param{unsigned long }{milliseconds}}
 242
 243 Pauses the thread execution for the given amount of time.
 244
 245 This function should be used instead of \helpref{wxSleep}{wxsleep} by all worker
 246 (i.e. all except the main one) threads.
 247
 248 \membersection{wxThread::Resume}\label{wxthreadresume}
 249
 250 \func{wxThreadError}{Resume}{\void}
 251
 252 Resumes a thread suspended by the call to \helpref{Pause}{wxthreadpause}.
 253
 254 This function can only be called from another thread context.
 255
 256 \membersection{wxThread::TestDestroy}\label{wxthreadtestdestroy}
 257
 258 \func{bool}{TestDestroy}{\void}
 259
 260 This function should be periodically called by the thread to ensure that calls
 261 to \helpref{Pause}{wxthreadpause} and \helpref{Delete}{wxthreaddelete} will
 262 work. If it returns TRUE, the thread should exit as soon as possible.
 263
 264 \membersection{wxThread::This}\label{wxthreadthis}
 265
 266 \func{static wxThread *}{This}{\void}
 267
 268 Return the thread object for the calling thread. NULL is returned if the calling thread
 269 is the main (GUI) thread, but \helpref{IsMain}{wxthreadismain} should be used to test
 270 whether the thread is really the main one because NULL may also be returned for the thread
 271 not created with wxThread class. Generally speaking, the return value for such thread
 272 is undefined.
 273
 274 \membersection{wxThread::Yield}\label{wxthreadyield}
 275
 276 \func{void}{Yield}{\void}
 277
 278 Give the rest of the thread time slice to the system allowing the other threads to run.
 279 See also \helpref{Sleep()}{wxthreadsleep}.
 280
 281 \membersection{wxThread::Wait}\label{wxthreadwait}
 282
 283 \constfunc{ExitCode}{Wait}{\void}
 284
 285 Waits until the thread terminates and returns its exit code or {\tt
 286 (ExitCode)-1} on error.
 287
 288 You can only Wait() for joinable (not detached) threads.
 289
 290 This function can only be called from another thread context.