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::GetCPUCount}\label{wxthreadgetcpucount}
 131
 132 \func{static int}{GetCPUCount}{\void}
 133
 134 Returns the number of system CPUs or -1 if the value is unknown.
 135
 136 \wxheading{See also}
 137
 138 \helpref{SetConcurrency}{wxthreadsetconcurrency}
 139
 140 \membersection{wxThread::GetId}\label{wxthreadgetid}
 141
 142 \constfunc{unsigned long}{GetId}{\void}
 143
 144 Gets the thread identifier: this is a platform dependent number which uniquely identifies the
 145 thread throughout the system during its existence (i.e. the thread identifiers may be reused).
 146
 147 \membersection{wxThread::GetPriority}\label{wxthreadgetpriority}
 148
 149 \constfunc{int}{GetPriority}{\void}
 150
 151 Gets the priority of the thread, between zero and 100.
 152
 153 The following priorities are defined:
 154
 155 \twocolwidtha{7cm}
 156 \begin{twocollist}\itemsep=0pt
 157 \twocolitem{{\bf WXTHREAD\_MIN\_PRIORITY}}{0}
 158 \twocolitem{{\bf WXTHREAD\_DEFAULT\_PRIORITY}}{50}
 159 \twocolitem{{\bf WXTHREAD\_MAX\_PRIORITY}}{100}
 160 \end{twocollist}
 161
 162 \membersection{wxThread::IsAlive}\label{wxthreadisalive}
 163
 164 \constfunc{bool}{IsAlive}{\void}
 165
 166 Returns TRUE if the thread is alive (i.e. started and not terminating).
 167
 168 \membersection{wxThread::IsDetached}\label{wxthreadisdetached}
 169
 170 \constfunc{bool}{IsDetached}{\void}
 171
 172 Returns TRUE if the thread is of detached kind, FALSE if it is a joinable one.
 173
 174 \membersection{wxThread::IsMain}\label{wxthreadismain}
 175
 176 \func{static bool}{IsMain}{\void}
 177
 178 Returns TRUE if the calling thread is the main application thread.
 179
 180 \membersection{wxThread::IsPaused}\label{wxthreadispaused}
 181
 182 \constfunc{bool}{IsPaused}{\void}
 183
 184 Returns TRUE if the thread is paused.
 185
 186 \membersection{wxThread::IsRunning}\label{wxthreadisrunning}
 187
 188 \constfunc{bool}{IsRunning}{\void}
 189
 190 Returns TRUE if the thread is running.
 191
 192 \membersection{wxThread::Kill}\label{wxthreadkill}
 193
 194 \func{wxThreadError}{Kill}{\void}
 195
 196 Immediately terminates the target thread. {\bf This function is dangerous and should
 197 be used with extreme care (and not used at all whenever possible)!} The resources
 198 allocated to the thread will not be freed and the state of the C runtime library
 199 may become inconsistent. Use \helpref{Delete()}{wxthreaddelete} instead.
 200
 201 For detached threads Kill() will also delete the associated C++ object.
 202
 203 This function can only be called from another thread context.
 204
 205 \membersection{wxThread::OnExit}\label{wxthreadonexit}
 206
 207 \func{void}{OnExit}{\void}
 208
 209 Called when the thread exits. This function is called in the context of the thread
 210 associated with the wxThread object, not in the context of the main thread.
 211
 212 This function should never be called directly.
 213
 214 \membersection{wxThread::Pause}\label{wxthreadpause}
 215
 216 \func{wxThreadError}{Pause}{\void}
 217
 218 Suspends the thread. Under some implementations (Win32), the thread is
 219 suspended immediately, under others it will only be suspended when it calls
 220 \helpref{TestDestroy}{wxthreadtestdestroy} for the next time (hence, if the
 221 thread doesn't call it at all, it won't be suspended).
 222
 223 This function can only be called from another thread context.
 224
 225 \membersection{wxThread::Run}\label{wxthreadrun}
 226
 227 \func{wxThreadError}{Run}{\void}
 228
 229 Starts the thread execution. Should be called after
 230 \helpref{Create}{wxthreadcreate}.
 231
 232 This function can only be called from another thread context.
 233
 234 \membersection{wxThread::SetPriority}\label{wxthreadsetpriority}
 235
 236 \func{void}{SetPriority}{\param{int}{ priority}}
 237
 238 Sets the priority of the thread, between zero and 100. This must be set before the thread is created.
 239
 240 The following priorities are already defined:
 241
 242 \twocolwidtha{7cm}
 243 \begin{twocollist}\itemsep=0pt
 244 \twocolitem{{\bf WXTHREAD\_MIN\_PRIORITY}}{0}
 245 \twocolitem{{\bf WXTHREAD\_DEFAULT\_PRIORITY}}{50}
 246 \twocolitem{{\bf WXTHREAD\_MAX\_PRIORITY}}{100}
 247 \end{twocollist}
 248
 249 \membersection{wxThread::Sleep}\label{wxthreadsleep}
 250
 251 \func{static void}{Sleep}{\param{unsigned long }{milliseconds}}
 252
 253 Pauses the thread execution for the given amount of time.
 254
 255 This function should be used instead of \helpref{wxSleep}{wxsleep} by all worker
 256 (i.e. all except the main one) threads.
 257
 258 \membersection{wxThread::Resume}\label{wxthreadresume}
 259
 260 \func{wxThreadError}{Resume}{\void}
 261
 262 Resumes a thread suspended by the call to \helpref{Pause}{wxthreadpause}.
 263
 264 This function can only be called from another thread context.
 265
 266 \membersection{wxThread::SetConcurrency}\label{wxthreadsetconcurrency}
 267
 268 \func{static bool}{SetConcurrency}{\param{size\_t }{level}}
 269
 270 Sets the thread concurrency level for this process. This is, roughly, the
 271 number of threads that the system tries to schedule to run in parallel.
 272 The value of $0$ for {\it level} may be used to set the default one.
 273
 274 Returns TRUE on success or FALSE otherwise (for example, if this function is
 275 not implemented for this platform (currently everything except Solaris)).
 276
 277 \membersection{wxThread::TestDestroy}\label{wxthreadtestdestroy}
 278
 279 \func{bool}{TestDestroy}{\void}
 280
 281 This function should be periodically called by the thread to ensure that calls
 282 to \helpref{Pause}{wxthreadpause} and \helpref{Delete}{wxthreaddelete} will
 283 work. If it returns TRUE, the thread should exit as soon as possible.
 284
 285 \membersection{wxThread::This}\label{wxthreadthis}
 286
 287 \func{static wxThread *}{This}{\void}
 288
 289 Return the thread object for the calling thread. NULL is returned if the calling thread
 290 is the main (GUI) thread, but \helpref{IsMain}{wxthreadismain} should be used to test
 291 whether the thread is really the main one because NULL may also be returned for the thread
 292 not created with wxThread class. Generally speaking, the return value for such thread
 293 is undefined.
 294
 295 \membersection{wxThread::Yield}\label{wxthreadyield}
 296
 297 \func{void}{Yield}{\void}
 298
 299 Give the rest of the thread time slice to the system allowing the other threads to run.
 300 See also \helpref{Sleep()}{wxthreadsleep}.
 301
 302 \membersection{wxThread::Wait}\label{wxthreadwait}
 303
 304 \constfunc{ExitCode}{Wait}{\void}
 305
 306 Waits until the thread terminates and returns its exit code or {\tt
 307 (ExitCode)-1} on error.
 308
 309 You can only Wait() for joinable (not detached) threads.
 310
 311 This function can only be called from another thread context.