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