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}{\param{unsigned int }{stackSize = 0}}
  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.  You may optionally
  81 specify the stack size to be allocated to it (Ignored on platforms that don't
  82 support setting it explicitly, eg. Unix).
  83
  84 \wxheading{Return value}
  85
  86 One of:
  87
  88 \twocolwidtha{7cm}
  89 \begin{twocollist}\itemsep=0pt
  90 \twocolitem{{\bf wxTHREAD\_NO\_ERROR}}{There was no error.}
  91 \twocolitem{{\bf wxTHREAD\_NO\_RESOURCE}}{There were insufficient resources to create a new thread.}
  92 \twocolitem{{\bf wxTHREAD\_RUNNING}}{The thread is already running.}
  93 \end{twocollist}
  94
  95 \membersection{wxThread::Delete}\label{wxthreaddelete}
  96
  97 \func{void}{Delete}{\void}
  98
  99 Calling \helpref{Delete}{wxthreaddelete} is a graceful way to terminate the
 100 thread. It asks the thread to terminate and, if the thread code is well
 101 written, the thread will terminate after the next call to
 102 \helpref{TestDestroy}{wxthreadtestdestroy} which should happen quite soon.
 103
 104 However, if the thread doesn't call \helpref{TestDestroy}{wxthreadtestdestroy}
 105 often enough (or at all), the function will not return immediately, but wait
 106 until the thread terminates. As it may take a long time, and the message processing
 107 is not stopped during this function execution, message handlers may be
 108 called from inside it!
 109
 110 Delete() may be called for thread in any state: running, paused or even not yet
 111 created. Moreover, it must be called if \helpref{Create}{wxthreadcreate} or
 112 \helpref{Run}{wxthreadrun} failed for a detached thread to free the memory
 113 occupied by the thread object. This cleanup will be done in the destructor for joinable
 114 threads.
 115
 116 Delete() may be called for a thread in any state: running, paused or even not yet created. Moreover,
 117 it must be called if \helpref{Create}{wxthreadcreate} or \helpref{Run}{wxthreadrun} fail to free
 118 the memory occupied by the thread object. However, you should not call Delete()
 119 on a detached thread which already terminated - doing so will probably result
 120 in a crash because the thread object doesn't exist any more.
 121
 122 For detached threads Delete() will also delete the C++ thread object, but it
 123 will not do this for joinable ones.
 124
 125 This function can only be called from another thread context.
 126
 127 \membersection{wxThread::Entry}\label{wxthreadentry}
 128
 129 \func{virtual ExitCode}{Entry}{\void}
 130
 131 This is the entry point of the thread. This function is pure virtual and must
 132 be implemented by any derived class. The thread execution will start here.
 133
 134 The returned value is the thread exit code which is only useful for
 135 joinable threads and is the value returned by \helpref{Wait}{wxthreadwait}.
 136
 137 This function is called by wxWindows itself and should never be called
 138 directly.
 139
 140 \membersection{wxThread::Exit}\label{wxthreadexit}
 141
 142 \func{void}{Exit}{\param{ExitCode }{exitcode = 0}}
 143
 144 This is a protected function of the wxThread class and thus can only be called
 145 from a derived class. It also can only be called in the context of this
 146 thread, i.e. a thread can only exit from itself, not from another thread.
 147
 148 This function will terminate the OS thread (i.e. stop the associated path of
 149 execution) and also delete the associated C++ object for detached threads.
 150 \helpref{wxThread::OnExit}{wxthreadonexit} will be called just before exiting.
 151
 152 \membersection{wxThread::GetCPUCount}\label{wxthreadgetcpucount}
 153
 154 \func{static int}{GetCPUCount}{\void}
 155
 156 Returns the number of system CPUs or -1 if the value is unknown.
 157
 158 \wxheading{See also}
 159
 160 \helpref{SetConcurrency}{wxthreadsetconcurrency}
 161
 162 \membersection{wxThread::GetId}\label{wxthreadgetid}
 163
 164 \constfunc{unsigned long}{GetId}{\void}
 165
 166 Gets the thread identifier: this is a platform dependent number that uniquely identifies the
 167 thread throughout the system during its existence (i.e. the thread identifiers may be reused).
 168
 169 \membersection{wxThread::GetPriority}\label{wxthreadgetpriority}
 170
 171 \constfunc{int}{GetPriority}{\void}
 172
 173 Gets the priority of the thread, between zero and 100.
 174
 175 The following priorities are defined:
 176
 177 \twocolwidtha{7cm}
 178 \begin{twocollist}\itemsep=0pt
 179 \twocolitem{{\bf WXTHREAD\_MIN\_PRIORITY}}{0}
 180 \twocolitem{{\bf WXTHREAD\_DEFAULT\_PRIORITY}}{50}
 181 \twocolitem{{\bf WXTHREAD\_MAX\_PRIORITY}}{100}
 182 \end{twocollist}
 183
 184 \membersection{wxThread::IsAlive}\label{wxthreadisalive}
 185
 186 \constfunc{bool}{IsAlive}{\void}
 187
 188 Returns TRUE if the thread is alive (i.e. started and not terminating).
 189
 190 \membersection{wxThread::IsDetached}\label{wxthreadisdetached}
 191
 192 \constfunc{bool}{IsDetached}{\void}
 193
 194 Returns TRUE if the thread is of the detached kind, FALSE if it is a joinable one.
 195
 196 \membersection{wxThread::IsMain}\label{wxthreadismain}
 197
 198 \func{static bool}{IsMain}{\void}
 199
 200 Returns TRUE if the calling thread is the main application thread.
 201
 202 \membersection{wxThread::IsPaused}\label{wxthreadispaused}
 203
 204 \constfunc{bool}{IsPaused}{\void}
 205
 206 Returns TRUE if the thread is paused.
 207
 208 \membersection{wxThread::IsRunning}\label{wxthreadisrunning}
 209
 210 \constfunc{bool}{IsRunning}{\void}
 211
 212 Returns TRUE if the thread is running.
 213
 214 \membersection{wxThread::Kill}\label{wxthreadkill}
 215
 216 \func{wxThreadError}{Kill}{\void}
 217
 218 Immediately terminates the target thread. {\bf This function is dangerous and should
 219 be used with extreme care (and not used at all whenever possible)!} The resources
 220 allocated to the thread will not be freed and the state of the C runtime library
 221 may become inconsistent. Use \helpref{Delete()}{wxthreaddelete} instead.
 222
 223 For detached threads Kill() will also delete the associated C++ object.
 224 However this will not happen for joinable threads and this means that you will
 225 still have to delete the wxThread object yourself to avoid memory leaks.
 226 In neither case \helpref{OnExit}{wxthreadonexit} of the dying thread will be
 227 called, so no thread-specific cleanup will be performed.
 228
 229 This function can only be called from another thread context, i.e. a thread
 230 cannot kill itself.
 231
 232 It is also an error to call this function for a thread which is not running or
 233 paused (in the latter case, the thread will be resumed first) - if you do it,
 234 a {\tt wxTHREAD\_NOT\_RUNNING} error will be returned.
 235
 236 \membersection{wxThread::OnExit}\label{wxthreadonexit}
 237
 238 \func{void}{OnExit}{\void}
 239
 240 Called when the thread exits. This function is called in the context of the
 241 thread associated with the wxThread object, not in the context of the main
 242 thread. This function will not be called if the thread was
 243 \helpref{killed}{wxthreadkill}.
 244
 245 This function should never be called directly.
 246
 247 \membersection{wxThread::Pause}\label{wxthreadpause}
 248
 249 \func{wxThreadError}{Pause}{\void}
 250
 251 Suspends the thread. Under some implementations (Win32), the thread is
 252 suspended immediately, under others it will only be suspended when it calls
 253 \helpref{TestDestroy}{wxthreadtestdestroy} for the next time (hence, if the
 254 thread doesn't call it at all, it won't be suspended).
 255
 256 This function can only be called from another thread context.
 257
 258 \membersection{wxThread::Run}\label{wxthreadrun}
 259
 260 \func{wxThreadError}{Run}{\void}
 261
 262 Starts the thread execution. Should be called after
 263 \helpref{Create}{wxthreadcreate}.
 264
 265 This function can only be called from another thread context.
 266
 267 \membersection{wxThread::SetPriority}\label{wxthreadsetpriority}
 268
 269 \func{void}{SetPriority}{\param{int}{ priority}}
 270
 271 Sets the priority of the thread, between $0$ and $100$. It can only be set
 272 after calling \helpref{Create()}{wxthreadcreate} but before calling
 273 \helpref{Run()}{wxthreadrun}.
 274
 275 The following priorities are already defined:
 276
 277 \twocolwidtha{7cm}
 278 \begin{twocollist}\itemsep=0pt
 279 \twocolitem{{\bf WXTHREAD\_MIN\_PRIORITY}}{0}
 280 \twocolitem{{\bf WXTHREAD\_DEFAULT\_PRIORITY}}{50}
 281 \twocolitem{{\bf WXTHREAD\_MAX\_PRIORITY}}{100}
 282 \end{twocollist}
 283
 284 \membersection{wxThread::Sleep}\label{wxthreadsleep}
 285
 286 \func{static void}{Sleep}{\param{unsigned long }{milliseconds}}
 287
 288 Pauses the thread execution for the given amount of time.
 289
 290 This function should be used instead of \helpref{wxSleep}{wxsleep} by all worker
 291 threads (i.e. all except the main one).
 292
 293 \membersection{wxThread::Resume}\label{wxthreadresume}
 294
 295 \func{wxThreadError}{Resume}{\void}
 296
 297 Resumes a thread suspended by the call to \helpref{Pause}{wxthreadpause}.
 298
 299 This function can only be called from another thread context.
 300
 301 \membersection{wxThread::SetConcurrency}\label{wxthreadsetconcurrency}
 302
 303 \func{static bool}{SetConcurrency}{\param{size\_t }{level}}
 304
 305 Sets the thread concurrency level for this process. This is, roughly, the
 306 number of threads that the system tries to schedule to run in parallel.
 307 The value of $0$ for {\it level} may be used to set the default one.
 308
 309 Returns TRUE on success or FALSE otherwise (for example, if this function is
 310 not implemented for this platform - currently everything except Solaris).
 311
 312 \membersection{wxThread::TestDestroy}\label{wxthreadtestdestroy}
 313
 314 \func{bool}{TestDestroy}{\void}
 315
 316 This function should be called periodically by the thread to ensure that calls
 317 to \helpref{Pause}{wxthreadpause} and \helpref{Delete}{wxthreaddelete} will
 318 work. If it returns TRUE, the thread should exit as soon as possible.
 319
 320 \membersection{wxThread::This}\label{wxthreadthis}
 321
 322 \func{static wxThread *}{This}{\void}
 323
 324 Return the thread object for the calling thread. NULL is returned if the calling thread
 325 is the main (GUI) thread, but \helpref{IsMain}{wxthreadismain} should be used to test
 326 whether the thread is really the main one because NULL may also be returned for the thread
 327 not created with wxThread class. Generally speaking, the return value for such a thread
 328 is undefined.
 329
 330 \membersection{wxThread::Yield}\label{wxthreadyield}
 331
 332 \func{void}{Yield}{\void}
 333
 334 Give the rest of the thread time slice to the system allowing the other threads to run.
 335 See also \helpref{Sleep()}{wxthreadsleep}.
 336
 337 \membersection{wxThread::Wait}\label{wxthreadwait}
 338
 339 \constfunc{ExitCode}{Wait}{\void}
 340
 341 Waits until the thread terminates and returns its exit code or {\tt (ExitCode)-1} on error.
 342
 343 You can only Wait() for joinable (not detached) threads.
 344
 345 This function can only be called from another thread context.
 346