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::GetCurrentId}\label{wxthreadgetcurrentid}
 163
 164 \func{static unsigned long}{GetCurrentId}{\void}
 165
 166 Returns the platform specific thread ID of the current thread as a
 167 long.  This can be used to uniquely identify threads, even if they are
 168 not wxThreads.
 169
 170 \membersection{wxThread::GetId}\label{wxthreadgetid}
 171
 172 \constfunc{unsigned long}{GetId}{\void}
 173
 174 Gets the thread identifier: this is a platform dependent number that uniquely identifies the
 175 thread throughout the system during its existence (i.e. the thread identifiers may be reused).
 176
 177 \membersection{wxThread::GetPriority}\label{wxthreadgetpriority}
 178
 179 \constfunc{int}{GetPriority}{\void}
 180
 181 Gets the priority of the thread, between zero and 100.
 182
 183 The following priorities are defined:
 184
 185 \twocolwidtha{7cm}
 186 \begin{twocollist}\itemsep=0pt
 187 \twocolitem{{\bf WXTHREAD\_MIN\_PRIORITY}}{0}
 188 \twocolitem{{\bf WXTHREAD\_DEFAULT\_PRIORITY}}{50}
 189 \twocolitem{{\bf WXTHREAD\_MAX\_PRIORITY}}{100}
 190 \end{twocollist}
 191
 192 \membersection{wxThread::IsAlive}\label{wxthreadisalive}
 193
 194 \constfunc{bool}{IsAlive}{\void}
 195
 196 Returns TRUE if the thread is alive (i.e. started and not terminating).
 197
 198 \membersection{wxThread::IsDetached}\label{wxthreadisdetached}
 199
 200 \constfunc{bool}{IsDetached}{\void}
 201
 202 Returns TRUE if the thread is of the detached kind, FALSE if it is a joinable one.
 203
 204 \membersection{wxThread::IsMain}\label{wxthreadismain}
 205
 206 \func{static bool}{IsMain}{\void}
 207
 208 Returns TRUE if the calling thread is the main application thread.
 209
 210 \membersection{wxThread::IsPaused}\label{wxthreadispaused}
 211
 212 \constfunc{bool}{IsPaused}{\void}
 213
 214 Returns TRUE if the thread is paused.
 215
 216 \membersection{wxThread::IsRunning}\label{wxthreadisrunning}
 217
 218 \constfunc{bool}{IsRunning}{\void}
 219
 220 Returns TRUE if the thread is running.
 221
 222 \membersection{wxThread::Kill}\label{wxthreadkill}
 223
 224 \func{wxThreadError}{Kill}{\void}
 225
 226 Immediately terminates the target thread. {\bf This function is dangerous and should
 227 be used with extreme care (and not used at all whenever possible)!} The resources
 228 allocated to the thread will not be freed and the state of the C runtime library
 229 may become inconsistent. Use \helpref{Delete()}{wxthreaddelete} instead.
 230
 231 For detached threads Kill() will also delete the associated C++ object.
 232 However this will not happen for joinable threads and this means that you will
 233 still have to delete the wxThread object yourself to avoid memory leaks.
 234 In neither case \helpref{OnExit}{wxthreadonexit} of the dying thread will be
 235 called, so no thread-specific cleanup will be performed.
 236
 237 This function can only be called from another thread context, i.e. a thread
 238 cannot kill itself.
 239
 240 It is also an error to call this function for a thread which is not running or
 241 paused (in the latter case, the thread will be resumed first) - if you do it,
 242 a {\tt wxTHREAD\_NOT\_RUNNING} error will be returned.
 243
 244 \membersection{wxThread::OnExit}\label{wxthreadonexit}
 245
 246 \func{void}{OnExit}{\void}
 247
 248 Called when the thread exits. This function is called in the context of the
 249 thread associated with the wxThread object, not in the context of the main
 250 thread. This function will not be called if the thread was
 251 \helpref{killed}{wxthreadkill}.
 252
 253 This function should never be called directly.
 254
 255 \membersection{wxThread::Pause}\label{wxthreadpause}
 256
 257 \func{wxThreadError}{Pause}{\void}
 258
 259 Suspends the thread. Under some implementations (Win32), the thread is
 260 suspended immediately, under others it will only be suspended when it calls
 261 \helpref{TestDestroy}{wxthreadtestdestroy} for the next time (hence, if the
 262 thread doesn't call it at all, it won't be suspended).
 263
 264 This function can only be called from another thread context.
 265
 266 \membersection{wxThread::Run}\label{wxthreadrun}
 267
 268 \func{wxThreadError}{Run}{\void}
 269
 270 Starts the thread execution. Should be called after
 271 \helpref{Create}{wxthreadcreate}.
 272
 273 This function can only be called from another thread context.
 274
 275 \membersection{wxThread::SetPriority}\label{wxthreadsetpriority}
 276
 277 \func{void}{SetPriority}{\param{int}{ priority}}
 278
 279 Sets the priority of the thread, between $0$ and $100$. It can only be set
 280 after calling \helpref{Create()}{wxthreadcreate} but before calling
 281 \helpref{Run()}{wxthreadrun}.
 282
 283 The following priorities are already defined:
 284
 285 \twocolwidtha{7cm}
 286 \begin{twocollist}\itemsep=0pt
 287 \twocolitem{{\bf WXTHREAD\_MIN\_PRIORITY}}{0}
 288 \twocolitem{{\bf WXTHREAD\_DEFAULT\_PRIORITY}}{50}
 289 \twocolitem{{\bf WXTHREAD\_MAX\_PRIORITY}}{100}
 290 \end{twocollist}
 291
 292 \membersection{wxThread::Sleep}\label{wxthreadsleep}
 293
 294 \func{static void}{Sleep}{\param{unsigned long }{milliseconds}}
 295
 296 Pauses the thread execution for the given amount of time.
 297
 298 This function should be used instead of \helpref{wxSleep}{wxsleep} by all worker
 299 threads (i.e. all except the main one).
 300
 301 \membersection{wxThread::Resume}\label{wxthreadresume}
 302
 303 \func{wxThreadError}{Resume}{\void}
 304
 305 Resumes a thread suspended by the call to \helpref{Pause}{wxthreadpause}.
 306
 307 This function can only be called from another thread context.
 308
 309 \membersection{wxThread::SetConcurrency}\label{wxthreadsetconcurrency}
 310
 311 \func{static bool}{SetConcurrency}{\param{size\_t }{level}}
 312
 313 Sets the thread concurrency level for this process. This is, roughly, the
 314 number of threads that the system tries to schedule to run in parallel.
 315 The value of $0$ for {\it level} may be used to set the default one.
 316
 317 Returns TRUE on success or FALSE otherwise (for example, if this function is
 318 not implemented for this platform - currently everything except Solaris).
 319
 320 \membersection{wxThread::TestDestroy}\label{wxthreadtestdestroy}
 321
 322 \func{bool}{TestDestroy}{\void}
 323
 324 This function should be called periodically by the thread to ensure that calls
 325 to \helpref{Pause}{wxthreadpause} and \helpref{Delete}{wxthreaddelete} will
 326 work. If it returns TRUE, the thread should exit as soon as possible.
 327
 328 \membersection{wxThread::This}\label{wxthreadthis}
 329
 330 \func{static wxThread *}{This}{\void}
 331
 332 Return the thread object for the calling thread. NULL is returned if the calling thread
 333 is the main (GUI) thread, but \helpref{IsMain}{wxthreadismain} should be used to test
 334 whether the thread is really the main one because NULL may also be returned for the thread
 335 not created with wxThread class. Generally speaking, the return value for such a thread
 336 is undefined.
 337
 338 \membersection{wxThread::Yield}\label{wxthreadyield}
 339
 340 \func{void}{Yield}{\void}
 341
 342 Give the rest of the thread time slice to the system allowing the other threads to run.
 343 See also \helpref{Sleep()}{wxthreadsleep}.
 344
 345 \membersection{wxThread::Wait}\label{wxthreadwait}
 346
 347 \constfunc{ExitCode}{Wait}{\void}
 348
 349 Waits until the thread terminates and returns its exit code or {\tt (ExitCode)-1} on error.
 350
 351 You can only Wait() for joinable (not detached) threads.
 352
 353 This function can only be called from another thread context.
 354