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
   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 the POSIX thread API (but unlike Win32 threads where all threads
  13 are joinable). The difference between the two is that only joinable threads
  14 can return a return code - this is returned by the Wait() function. Detached
  15 threads (the default type) cannot 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 or the
  19 system resources used by it will never be freed, and you also must delete the
  20 corresponding wxThread object yourself. In contrast, 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. Joinable
  26 threads may be created on the stack although more usually they will be created
  27 on the heap as well. Don't create global thread objects because they allocate
  28 memory in their constructor, which will cause problems for the memory checking
  29 system.
  30
  31 \wxheading{Derived from}
  32
  33 None.
  34
  35 \wxheading{Include files}
  36
  37 <wx/thread.h>
  38
  39 \wxheading{See also}
  40
  41 \helpref{wxMutex}{wxmutex}, \helpref{wxCondition}{wxcondition}, \helpref{wxCriticalSection}{wxcriticalsection}
  42
  43 \latexignore{\rtfignore{\wxheading{Members}}}
  44
  45 \membersection{wxThread::wxThread}\label{wxthreadctor}
  46
  47 \func{}{wxThread}{\param{wxThreadKind }{kind = wxTHREAD\_DETACHED}}
  48
  49 This constructor creates a new detached (default) or joinable C++ thread object. It
  50 does not create or start execution of the real thread - for this you should
  51 use the \helpref{Create}{wxthreadcreate} and \helpref{Run}{wxthreadrun} methods.
  52
  53 The possible values for {\it kind} parameters are:
  54
  55 \twocolwidtha{7cm}
  56 \begin{twocollist}\itemsep=0pt
  57 \twocolitem{{\bf wxTHREAD\_DETACHED}}{Create a detached thread.}
  58 \twocolitem{{\bf wxTHREAD\_JOINABLE}}{Create a joinable thread}
  59 \end{twocollist}
  60
  61 \membersection{wxThread::\destruct{wxThread}}
  62
  63 \func{}{\destruct{wxThread}}{\void}
  64
  65 The destructor frees the resources associated with the thread. Notice that you
  66 should never delete a detached thread - you may only call
  67 \helpref{Delete}{wxthreaddelete} on it or wait until it terminates (and auto
  68 destructs) itself. Because the detached threads delete themselves, they can
  69 only be allocated on the heap.
  70
  71 Joinable threads should be deleted explicitly. The \helpref{Delete}{wxthreaddelete} and \helpref{Kill}{wxthreadkill} functions
  72 will not delete the C++ thread object. It is also safe to allocate them on
  73 stack.
  74
  75 \membersection{wxThread::Create}\label{wxthreadcreate}
  76
  77 \func{wxThreadError}{Create}{\void}
  78
  79 Creates a new thread. The thread object is created in the suspended state, and you
  80 should call \helpref{Run}{wxthreadrun} to start running it.
  81
  82 \wxheading{Return value}
  83
  84 One of:
  85
  86 \twocolwidtha{7cm}
  87 \begin{twocollist}\itemsep=0pt
  88 \twocolitem{{\bf wxTHREAD\_NO\_ERROR}}{There was no error.}
  89 \twocolitem{{\bf wxTHREAD\_NO\_RESOURCE}}{There were insufficient resources to create a new thread.}
  90 \twocolitem{{\bf wxTHREAD\_RUNNING}}{The thread is already running.}
  91 \end{twocollist}
  92
  93 \membersection{wxThread::Delete}\label{wxthreaddelete}
  94
  95 \func{void}{Delete}{\void}
  96
  97 Calling \helpref{Delete}{wxthreaddelete} is a graceful way to terminate the
  98 thread. It asks the thread to terminate and, if the thread code is well
  99 written, the thread will terminate after the next call to
 100 \helpref{TestDestroy}{wxthreadtestdestroy} which should happen quite soon.
 101
 102 However, if the thread doesn't call \helpref{TestDestroy}{wxthreadtestdestroy}
 103 often enough (or at all), the function will not return immediately, but wait
 104 until the thread terminates. As it may take a long time, and the message processing
 105 is not stopped during this function execution, message handlers may be
 106 called from inside it!
 107
 108 Delete() may be called for thread in any state: running, paused or even not yet
 109 created. Moreover, it must be called if \helpref{Create}{wxthreadcreate} or
 110 \helpref{Run}{wxthreadrun} failed for a detached thread to free the memory
 111 occupied by the thread object. This cleanup will be done in the destructor for joinable
 112 threads.
 113
 114 Delete() may be called for a thread in any state: running, paused or even not yet created. Moreover,
 115 it must be called if \helpref{Create}{wxthreadcreate} or \helpref{Run}{wxthreadrun} fail to free
 116 the memory occupied by the thread object. However, you should not call Delete()
 117 on a detached thread which already terminated - doing so will probably result
 118 in a crash because the thread object doesn't exist any more.
 119
 120 For detached threads Delete() will also delete the C++ thread object, but it
 121 will not do this for joinable ones.
 122
 123 This function can only be called from another thread context.
 124
 125 \membersection{wxThread::Entry}\label{wxthreadentry}
 126
 127 \func{virtual ExitCode}{Entry}{\void}
 128
 129 This is the entry point of the thread. This function is pure virtual and must
 130 be implemented by any derived class. The thread execution will start here.
 131
 132 The returned value is the thread exit code which is only useful for
 133 joinable threads and is the value returned by \helpref{Wait}{wxthreadwait}.
 134
 135 This function is called by wxWindows itself and should never be called
 136 directly.
 137
 138 \membersection{wxThread::Exit}\label{wxthreadexit}
 139
 140 \func{void}{Exit}{\param{ExitCode }{exitcode = 0}}
 141
 142 This is a protected function of the wxThread class and thus can only be called
 143 from a derived class. It also can only be called in the context of this
 144 thread, i.e. a thread can only exit from itself, not from another thread.
 145
 146 This function will terminate the OS thread (i.e. stop the associated path of
 147 execution) and also delete the associated C++ object for detached threads.
 148 \helpref{wxThread::OnExit}{wxthreadonexit} will be called just before exiting.
 149
 150 \membersection{wxThread::GetCPUCount}\label{wxthreadgetcpucount}
 151
 152 \func{static int}{GetCPUCount}{\void}
 153
 154 Returns the number of system CPUs or -1 if the value is unknown.
 155
 156 \wxheading{See also}
 157
 158 \helpref{SetConcurrency}{wxthreadsetconcurrency}
 159
 160 \membersection{wxThread::GetId}\label{wxthreadgetid}
 161
 162 \constfunc{unsigned long}{GetId}{\void}
 163
 164 Gets the thread identifier: this is a platform dependent number that uniquely identifies the
 165 thread throughout the system during its existence (i.e. the thread identifiers may be reused).
 166
 167 \membersection{wxThread::GetPriority}\label{wxthreadgetpriority}
 168
 169 \constfunc{int}{GetPriority}{\void}
 170
 171 Gets the priority of the thread, between zero and 100.
 172
 173 The following priorities are defined:
 174
 175 \twocolwidtha{7cm}
 176 \begin{twocollist}\itemsep=0pt
 177 \twocolitem{{\bf WXTHREAD\_MIN\_PRIORITY}}{0}
 178 \twocolitem{{\bf WXTHREAD\_DEFAULT\_PRIORITY}}{50}
 179 \twocolitem{{\bf WXTHREAD\_MAX\_PRIORITY}}{100}
 180 \end{twocollist}
 181
 182 \membersection{wxThread::IsAlive}\label{wxthreadisalive}
 183
 184 \constfunc{bool}{IsAlive}{\void}
 185
 186 Returns TRUE if the thread is alive (i.e. started and not terminating).
 187
 188 \membersection{wxThread::IsDetached}\label{wxthreadisdetached}
 189
 190 \constfunc{bool}{IsDetached}{\void}
 191
 192 Returns TRUE if the thread is of the detached kind, FALSE if it is a joinable one.
 193
 194 \membersection{wxThread::IsMain}\label{wxthreadismain}
 195
 196 \func{static bool}{IsMain}{\void}
 197
 198 Returns TRUE if the calling thread is the main application thread.
 199
 200 \membersection{wxThread::IsPaused}\label{wxthreadispaused}
 201
 202 \constfunc{bool}{IsPaused}{\void}
 203
 204 Returns TRUE if the thread is paused.
 205
 206 \membersection{wxThread::IsRunning}\label{wxthreadisrunning}
 207
 208 \constfunc{bool}{IsRunning}{\void}
 209
 210 Returns TRUE if the thread is running.
 211
 212 \membersection{wxThread::Kill}\label{wxthreadkill}
 213
 214 \func{wxThreadError}{Kill}{\void}
 215
 216 Immediately terminates the target thread. {\bf This function is dangerous and should
 217 be used with extreme care (and not used at all whenever possible)!} The resources
 218 allocated to the thread will not be freed and the state of the C runtime library
 219 may become inconsistent. Use \helpref{Delete()}{wxthreaddelete} instead.
 220
 221 For detached threads Kill() will also delete the associated C++ object.
 222 However this will not happen for joinable threads and this means that you will
 223 still have to delete the wxThread object yourself to avoid memory leaks.
 224 In neither case \helpref{OnExit}{wxthreadonexit} of the dying thread will be
 225 called, so no thread-specific cleanup will be performed.
 226
 227 This function can only be called from another thread context, i.e. a thread
 228 cannot kill itself.
 229
 230 It is also an error to call this function for a thread which is not running or
 231 paused (in the latter case, the thread will be resumed first) - if you do it,
 232 a {\tt wxTHREAD\_NOT\_RUNNING} error will be returned.
 233
 234 \membersection{wxThread::OnExit}\label{wxthreadonexit}
 235
 236 \func{void}{OnExit}{\void}
 237
 238 Called when the thread exits. This function is called in the context of the
 239 thread associated with the wxThread object, not in the context of the main
 240 thread. This function will not be called if the thread was
 241 \helpref{killed}{wxthreadkill}.
 242
 243 This function should never be called directly.
 244
 245 \membersection{wxThread::Pause}\label{wxthreadpause}
 246
 247 \func{wxThreadError}{Pause}{\void}
 248
 249 Suspends the thread. Under some implementations (Win32), the thread is
 250 suspended immediately, under others it will only be suspended when it calls
 251 \helpref{TestDestroy}{wxthreadtestdestroy} for the next time (hence, if the
 252 thread doesn't call it at all, it won't be suspended).
 253
 254 This function can only be called from another thread context.
 255
 256 \membersection{wxThread::Run}\label{wxthreadrun}
 257
 258 \func{wxThreadError}{Run}{\void}
 259
 260 Starts the thread execution. Should be called after
 261 \helpref{Create}{wxthreadcreate}.
 262
 263 This function can only be called from another thread context.
 264
 265 \membersection{wxThread::SetPriority}\label{wxthreadsetpriority}
 266
 267 \func{void}{SetPriority}{\param{int}{ priority}}
 268
 269 Sets the priority of the thread, between zero and 100. This must be set before the thread is created.
 270
 271 The following priorities are already defined:
 272
 273 \twocolwidtha{7cm}
 274 \begin{twocollist}\itemsep=0pt
 275 \twocolitem{{\bf WXTHREAD\_MIN\_PRIORITY}}{0}
 276 \twocolitem{{\bf WXTHREAD\_DEFAULT\_PRIORITY}}{50}
 277 \twocolitem{{\bf WXTHREAD\_MAX\_PRIORITY}}{100}
 278 \end{twocollist}
 279
 280 \membersection{wxThread::Sleep}\label{wxthreadsleep}
 281
 282 \func{static void}{Sleep}{\param{unsigned long }{milliseconds}}
 283
 284 Pauses the thread execution for the given amount of time.
 285
 286 This function should be used instead of \helpref{wxSleep}{wxsleep} by all worker
 287 threads (i.e. all except the main one).
 288
 289 \membersection{wxThread::Resume}\label{wxthreadresume}
 290
 291 \func{wxThreadError}{Resume}{\void}
 292
 293 Resumes a thread suspended by the call to \helpref{Pause}{wxthreadpause}.
 294
 295 This function can only be called from another thread context.
 296
 297 \membersection{wxThread::SetConcurrency}\label{wxthreadsetconcurrency}
 298
 299 \func{static bool}{SetConcurrency}{\param{size\_t }{level}}
 300
 301 Sets the thread concurrency level for this process. This is, roughly, the
 302 number of threads that the system tries to schedule to run in parallel.
 303 The value of $0$ for {\it level} may be used to set the default one.
 304
 305 Returns TRUE on success or FALSE otherwise (for example, if this function is
 306 not implemented for this platform - currently everything except Solaris).
 307
 308 \membersection{wxThread::TestDestroy}\label{wxthreadtestdestroy}
 309
 310 \func{bool}{TestDestroy}{\void}
 311
 312 This function should be called periodically by the thread to ensure that calls
 313 to \helpref{Pause}{wxthreadpause} and \helpref{Delete}{wxthreaddelete} will
 314 work. If it returns TRUE, the thread should exit as soon as possible.
 315
 316 \membersection{wxThread::This}\label{wxthreadthis}
 317
 318 \func{static wxThread *}{This}{\void}
 319
 320 Return the thread object for the calling thread. NULL is returned if the calling thread
 321 is the main (GUI) thread, but \helpref{IsMain}{wxthreadismain} should be used to test
 322 whether the thread is really the main one because NULL may also be returned for the thread
 323 not created with wxThread class. Generally speaking, the return value for such a thread
 324 is undefined.
 325
 326 \membersection{wxThread::Yield}\label{wxthreadyield}
 327
 328 \func{void}{Yield}{\void}
 329
 330 Give the rest of the thread time slice to the system allowing the other threads to run.
 331 See also \helpref{Sleep()}{wxthreadsleep}.
 332
 333 \membersection{wxThread::Wait}\label{wxthreadwait}
 334
 335 \constfunc{ExitCode}{Wait}{\void}
 336
 337 Waits until the thread terminates and returns its exit code or {\tt (ExitCode)-1} on error.
 338
 339 You can only Wait() for joinable (not detached) threads.
 340
 341 This function can only be called from another thread context.
 342