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::Exit}\label{wxthreadexit}
 131
 132 \func{void}{Exit}{\param{ExitCode }{exitcode = 0}}
 133
 134 This is a protected function of wxThread class and thus can be called only
 135 from a derived class. It also can be called only in the context of this
 136 thread, i.e. a thread can only exit from itself, not from another thread.
 137
 138 This function will terminate the OS thread (i.e. stop the associated path of
 139 execution) and also delete the associated C++ object for detached threads.
 140 \helpref{wxThread::OnExit}{wxthreadonexit} will be called just before exiting.
 141
 142 \membersection{wxThread::GetCPUCount}\label{wxthreadgetcpucount}
 143
 144 \func{static int}{GetCPUCount}{\void}
 145
 146 Returns the number of system CPUs or -1 if the value is unknown.
 147
 148 \wxheading{See also}
 149
 150 \helpref{SetConcurrency}{wxthreadsetconcurrency}
 151
 152 \membersection{wxThread::GetId}\label{wxthreadgetid}
 153
 154 \constfunc{unsigned long}{GetId}{\void}
 155
 156 Gets the thread identifier: this is a platform dependent number which uniquely identifies the
 157 thread throughout the system during its existence (i.e. the thread identifiers may be reused).
 158
 159 \membersection{wxThread::GetPriority}\label{wxthreadgetpriority}
 160
 161 \constfunc{int}{GetPriority}{\void}
 162
 163 Gets the priority of the thread, between zero and 100.
 164
 165 The following priorities are defined:
 166
 167 \twocolwidtha{7cm}
 168 \begin{twocollist}\itemsep=0pt
 169 \twocolitem{{\bf WXTHREAD\_MIN\_PRIORITY}}{0}
 170 \twocolitem{{\bf WXTHREAD\_DEFAULT\_PRIORITY}}{50}
 171 \twocolitem{{\bf WXTHREAD\_MAX\_PRIORITY}}{100}
 172 \end{twocollist}
 173
 174 \membersection{wxThread::IsAlive}\label{wxthreadisalive}
 175
 176 \constfunc{bool}{IsAlive}{\void}
 177
 178 Returns TRUE if the thread is alive (i.e. started and not terminating).
 179
 180 \membersection{wxThread::IsDetached}\label{wxthreadisdetached}
 181
 182 \constfunc{bool}{IsDetached}{\void}
 183
 184 Returns TRUE if the thread is of detached kind, FALSE if it is a joinable one.
 185
 186 \membersection{wxThread::IsMain}\label{wxthreadismain}
 187
 188 \func{static bool}{IsMain}{\void}
 189
 190 Returns TRUE if the calling thread is the main application thread.
 191
 192 \membersection{wxThread::IsPaused}\label{wxthreadispaused}
 193
 194 \constfunc{bool}{IsPaused}{\void}
 195
 196 Returns TRUE if the thread is paused.
 197
 198 \membersection{wxThread::IsRunning}\label{wxthreadisrunning}
 199
 200 \constfunc{bool}{IsRunning}{\void}
 201
 202 Returns TRUE if the thread is running.
 203
 204 \membersection{wxThread::Kill}\label{wxthreadkill}
 205
 206 \func{wxThreadError}{Kill}{\void}
 207
 208 Immediately terminates the target thread. {\bf This function is dangerous and should
 209 be used with extreme care (and not used at all whenever possible)!} The resources
 210 allocated to the thread will not be freed and the state of the C runtime library
 211 may become inconsistent. Use \helpref{Delete()}{wxthreaddelete} instead.
 212
 213 For detached threads Kill() will also delete the associated C++ object,
 214 however this will not happen for joinable threads and this means that you will
 215 still have to delete the wxThread object yourself to avoid memory leaks.
 216 In neither case \helpref{OnExit}{wxthreadonexit} of the dying thread will be
 217 called, so no thread-specific cleanup will be performed.
 218
 219 This function can only be called from another thread context, i.e. a thread
 220 can not kill itself.
 221
 222 It is also an error to call this function for a thread which is not running or
 223 paused (in the latter case, the thread will be resumed first) - if you do it,
 224 {\tt wxTHREAD\_NOT\_RUNNING} error will be returned.
 225
 226 \membersection{wxThread::OnExit}\label{wxthreadonexit}
 227
 228 \func{void}{OnExit}{\void}
 229
 230 Called when the thread exits. This function is called in the context of the
 231 thread associated with the wxThread object, not in the context of the main
 232 thread. This function will not be called if the thread was
 233 \helpref{killed}{wxthreadkill}.
 234
 235 This function should never be called directly.
 236
 237 \membersection{wxThread::Pause}\label{wxthreadpause}
 238
 239 \func{wxThreadError}{Pause}{\void}
 240
 241 Suspends the thread. Under some implementations (Win32), the thread is
 242 suspended immediately, under others it will only be suspended when it calls
 243 \helpref{TestDestroy}{wxthreadtestdestroy} for the next time (hence, if the
 244 thread doesn't call it at all, it won't be suspended).
 245
 246 This function can only be called from another thread context.
 247
 248 \membersection{wxThread::Run}\label{wxthreadrun}
 249
 250 \func{wxThreadError}{Run}{\void}
 251
 252 Starts the thread execution. Should be called after
 253 \helpref{Create}{wxthreadcreate}.
 254
 255 This function can only be called from another thread context.
 256
 257 \membersection{wxThread::SetPriority}\label{wxthreadsetpriority}
 258
 259 \func{void}{SetPriority}{\param{int}{ priority}}
 260
 261 Sets the priority of the thread, between zero and 100. This must be set before the thread is created.
 262
 263 The following priorities are already defined:
 264
 265 \twocolwidtha{7cm}
 266 \begin{twocollist}\itemsep=0pt
 267 \twocolitem{{\bf WXTHREAD\_MIN\_PRIORITY}}{0}
 268 \twocolitem{{\bf WXTHREAD\_DEFAULT\_PRIORITY}}{50}
 269 \twocolitem{{\bf WXTHREAD\_MAX\_PRIORITY}}{100}
 270 \end{twocollist}
 271
 272 \membersection{wxThread::Sleep}\label{wxthreadsleep}
 273
 274 \func{static void}{Sleep}{\param{unsigned long }{milliseconds}}
 275
 276 Pauses the thread execution for the given amount of time.
 277
 278 This function should be used instead of \helpref{wxSleep}{wxsleep} by all worker
 279 (i.e. all except the main one) threads.
 280
 281 \membersection{wxThread::Resume}\label{wxthreadresume}
 282
 283 \func{wxThreadError}{Resume}{\void}
 284
 285 Resumes a thread suspended by the call to \helpref{Pause}{wxthreadpause}.
 286
 287 This function can only be called from another thread context.
 288
 289 \membersection{wxThread::SetConcurrency}\label{wxthreadsetconcurrency}
 290
 291 \func{static bool}{SetConcurrency}{\param{size\_t }{level}}
 292
 293 Sets the thread concurrency level for this process. This is, roughly, the
 294 number of threads that the system tries to schedule to run in parallel.
 295 The value of $0$ for {\it level} may be used to set the default one.
 296
 297 Returns TRUE on success or FALSE otherwise (for example, if this function is
 298 not implemented for this platform (currently everything except Solaris)).
 299
 300 \membersection{wxThread::TestDestroy}\label{wxthreadtestdestroy}
 301
 302 \func{bool}{TestDestroy}{\void}
 303
 304 This function should be periodically called by the thread to ensure that calls
 305 to \helpref{Pause}{wxthreadpause} and \helpref{Delete}{wxthreaddelete} will
 306 work. If it returns TRUE, the thread should exit as soon as possible.
 307
 308 \membersection{wxThread::This}\label{wxthreadthis}
 309
 310 \func{static wxThread *}{This}{\void}
 311
 312 Return the thread object for the calling thread. NULL is returned if the calling thread
 313 is the main (GUI) thread, but \helpref{IsMain}{wxthreadismain} should be used to test
 314 whether the thread is really the main one because NULL may also be returned for the thread
 315 not created with wxThread class. Generally speaking, the return value for such thread
 316 is undefined.
 317
 318 \membersection{wxThread::Yield}\label{wxthreadyield}
 319
 320 \func{void}{Yield}{\void}
 321
 322 Give the rest of the thread time slice to the system allowing the other threads to run.
 323 See also \helpref{Sleep()}{wxthreadsleep}.
 324
 325 \membersection{wxThread::Wait}\label{wxthreadwait}
 326
 327 \constfunc{ExitCode}{Wait}{\void}
 328
 329 Waits until the thread terminates and returns its exit code or {\tt
 330 (ExitCode)-1} on error.
 331
 332 You can only Wait() for joinable (not detached) threads.
 333
 334 This function can only be called from another thread context.
 335