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 a thread in any state: running, paused or even not
 111 yet created. Moreover, it must be called if \helpref{Create}{wxthreadcreate} or
 112 \helpref{Run}{wxthreadrun} fail in order to free the memory occupied by the
 113 thread object. However, you should not call Delete() on a detached thread which
 114 already terminated -- doing so will probably result in a crash because the
 115 thread object doesn't exist any more.
 116
 117 For detached threads Delete() will also delete the C++ thread object, but it
 118 will not do this for joinable ones.
 119
 120 This function can only be called from another thread context.
 121
 122 \membersection{wxThread::Entry}\label{wxthreadentry}
 123
 124 \func{virtual ExitCode}{Entry}{\void}
 125
 126 This is the entry point of the thread. This function is pure virtual and must
 127 be implemented by any derived class. The thread execution will start here.
 128
 129 The returned value is the thread exit code which is only useful for
 130 joinable threads and is the value returned by \helpref{Wait}{wxthreadwait}.
 131
 132 This function is called by wxWindows itself and should never be called
 133 directly.
 134
 135 \membersection{wxThread::Exit}\label{wxthreadexit}
 136
 137 \func{void}{Exit}{\param{ExitCode }{exitcode = 0}}
 138
 139 This is a protected function of the wxThread class and thus can only be called
 140 from a derived class. It also can only be called in the context of this
 141 thread, i.e. a thread can only exit from itself, not from another thread.
 142
 143 This function will terminate the OS thread (i.e. stop the associated path of
 144 execution) and also delete the associated C++ object for detached threads.
 145 \helpref{wxThread::OnExit}{wxthreadonexit} will be called just before exiting.
 146
 147 \membersection{wxThread::GetCPUCount}\label{wxthreadgetcpucount}
 148
 149 \func{static int}{GetCPUCount}{\void}
 150
 151 Returns the number of system CPUs or -1 if the value is unknown.
 152
 153 \wxheading{See also}
 154
 155 \helpref{SetConcurrency}{wxthreadsetconcurrency}
 156
 157 \membersection{wxThread::GetCurrentId}\label{wxthreadgetcurrentid}
 158
 159 \func{static unsigned long}{GetCurrentId}{\void}
 160
 161 Returns the platform specific thread ID of the current thread as a
 162 long.  This can be used to uniquely identify threads, even if they are
 163 not wxThreads.
 164
 165 \membersection{wxThread::GetId}\label{wxthreadgetid}
 166
 167 \constfunc{unsigned long}{GetId}{\void}
 168
 169 Gets the thread identifier: this is a platform dependent number that uniquely identifies the
 170 thread throughout the system during its existence (i.e. the thread identifiers may be reused).
 171
 172 \membersection{wxThread::GetPriority}\label{wxthreadgetpriority}
 173
 174 \constfunc{int}{GetPriority}{\void}
 175
 176 Gets the priority of the thread, between zero and 100.
 177
 178 The following priorities are defined:
 179
 180 \twocolwidtha{7cm}
 181 \begin{twocollist}\itemsep=0pt
 182 \twocolitem{{\bf WXTHREAD\_MIN\_PRIORITY}}{0}
 183 \twocolitem{{\bf WXTHREAD\_DEFAULT\_PRIORITY}}{50}
 184 \twocolitem{{\bf WXTHREAD\_MAX\_PRIORITY}}{100}
 185 \end{twocollist}
 186
 187 \membersection{wxThread::IsAlive}\label{wxthreadisalive}
 188
 189 \constfunc{bool}{IsAlive}{\void}
 190
 191 Returns true if the thread is alive (i.e. started and not terminating).
 192
 193 \membersection{wxThread::IsDetached}\label{wxthreadisdetached}
 194
 195 \constfunc{bool}{IsDetached}{\void}
 196
 197 Returns true if the thread is of the detached kind, false if it is a joinable one.
 198
 199 \membersection{wxThread::IsMain}\label{wxthreadismain}
 200
 201 \func{static bool}{IsMain}{\void}
 202
 203 Returns true if the calling thread is the main application thread.
 204
 205 \membersection{wxThread::IsPaused}\label{wxthreadispaused}
 206
 207 \constfunc{bool}{IsPaused}{\void}
 208
 209 Returns true if the thread is paused.
 210
 211 \membersection{wxThread::IsRunning}\label{wxthreadisrunning}
 212
 213 \constfunc{bool}{IsRunning}{\void}
 214
 215 Returns true if the thread is running.
 216
 217 \membersection{wxThread::Kill}\label{wxthreadkill}
 218
 219 \func{wxThreadError}{Kill}{\void}
 220
 221 Immediately terminates the target thread. {\bf This function is dangerous and should
 222 be used with extreme care (and not used at all whenever possible)!} The resources
 223 allocated to the thread will not be freed and the state of the C runtime library
 224 may become inconsistent. Use \helpref{Delete()}{wxthreaddelete} instead.
 225
 226 For detached threads Kill() will also delete the associated C++ object.
 227 However this will not happen for joinable threads and this means that you will
 228 still have to delete the wxThread object yourself to avoid memory leaks.
 229 In neither case \helpref{OnExit}{wxthreadonexit} of the dying thread will be
 230 called, so no thread-specific cleanup will be performed.
 231
 232 This function can only be called from another thread context, i.e. a thread
 233 cannot kill itself.
 234
 235 It is also an error to call this function for a thread which is not running or
 236 paused (in the latter case, the thread will be resumed first) -- if you do it,
 237 a {\tt wxTHREAD\_NOT\_RUNNING} error will be returned.
 238
 239 \membersection{wxThread::OnExit}\label{wxthreadonexit}
 240
 241 \func{void}{OnExit}{\void}
 242
 243 Called when the thread exits. This function is called in the context of the
 244 thread associated with the wxThread object, not in the context of the main
 245 thread. This function will not be called if the thread was
 246 \helpref{killed}{wxthreadkill}.
 247
 248 This function should never be called directly.
 249
 250 \membersection{wxThread::Pause}\label{wxthreadpause}
 251
 252 \func{wxThreadError}{Pause}{\void}
 253
 254 Suspends the thread. Under some implementations (Win32), the thread is
 255 suspended immediately, under others it will only be suspended when it calls
 256 \helpref{TestDestroy}{wxthreadtestdestroy} for the next time (hence, if the
 257 thread doesn't call it at all, it won't be suspended).
 258
 259 This function can only be called from another thread context.
 260
 261 \membersection{wxThread::Run}\label{wxthreadrun}
 262
 263 \func{wxThreadError}{Run}{\void}
 264
 265 Starts the thread execution. Should be called after
 266 \helpref{Create}{wxthreadcreate}.
 267
 268 This function can only be called from another thread context.
 269
 270 \membersection{wxThread::SetPriority}\label{wxthreadsetpriority}
 271
 272 \func{void}{SetPriority}{\param{int}{ priority}}
 273
 274 Sets the priority of the thread, between $0$ and $100$. It can only be set
 275 after calling \helpref{Create()}{wxthreadcreate} but before calling
 276 \helpref{Run()}{wxthreadrun}.
 277
 278 The following priorities are already defined:
 279
 280 \twocolwidtha{7cm}
 281 \begin{twocollist}\itemsep=0pt
 282 \twocolitem{{\bf WXTHREAD\_MIN\_PRIORITY}}{0}
 283 \twocolitem{{\bf WXTHREAD\_DEFAULT\_PRIORITY}}{50}
 284 \twocolitem{{\bf WXTHREAD\_MAX\_PRIORITY}}{100}
 285 \end{twocollist}
 286
 287 \membersection{wxThread::Sleep}\label{wxthreadsleep}
 288
 289 \func{static void}{Sleep}{\param{unsigned long }{milliseconds}}
 290
 291 Pauses the thread execution for the given amount of time.
 292
 293 This function should be used instead of \helpref{wxSleep}{wxsleep} by all worker
 294 threads (i.e. all except the main one).
 295
 296 \membersection{wxThread::Resume}\label{wxthreadresume}
 297
 298 \func{wxThreadError}{Resume}{\void}
 299
 300 Resumes a thread suspended by the call to \helpref{Pause}{wxthreadpause}.
 301
 302 This function can only be called from another thread context.
 303
 304 \membersection{wxThread::SetConcurrency}\label{wxthreadsetconcurrency}
 305
 306 \func{static bool}{SetConcurrency}{\param{size\_t }{level}}
 307
 308 Sets the thread concurrency level for this process. This is, roughly, the
 309 number of threads that the system tries to schedule to run in parallel.
 310 The value of $0$ for {\it level} may be used to set the default one.
 311
 312 Returns true on success or false otherwise (for example, if this function is
 313 not implemented for this platform -- currently everything except Solaris).
 314
 315 \membersection{wxThread::TestDestroy}\label{wxthreadtestdestroy}
 316
 317 \func{bool}{TestDestroy}{\void}
 318
 319 This function should be called periodically by the thread to ensure that calls
 320 to \helpref{Pause}{wxthreadpause} and \helpref{Delete}{wxthreaddelete} will
 321 work. If it returns true, the thread should exit as soon as possible.
 322
 323 \membersection{wxThread::This}\label{wxthreadthis}
 324
 325 \func{static wxThread *}{This}{\void}
 326
 327 Return the thread object for the calling thread. NULL is returned if the calling thread
 328 is the main (GUI) thread, but \helpref{IsMain}{wxthreadismain} should be used to test
 329 whether the thread is really the main one because NULL may also be returned for the thread
 330 not created with wxThread class. Generally speaking, the return value for such a thread
 331 is undefined.
 332
 333 \membersection{wxThread::Yield}\label{wxthreadyield}
 334
 335 \func{void}{Yield}{\void}
 336
 337 Give the rest of the thread time slice to the system allowing the other threads to run.
 338 See also \helpref{Sleep()}{wxthreadsleep}.
 339
 340 \membersection{wxThread::Wait}\label{wxthreadwait}
 341
 342 \constfunc{ExitCode}{Wait}{\void}
 343
 344 Waits until the thread terminates and returns its exit code or {\tt (ExitCode)-1} on error.
 345
 346 You can only Wait() for joinable (not detached) threads.
 347
 348 This function can only be called from another thread context.
 349