include/SDL_thread.h

/*
  Simple DirectMedia Layer
  Copyright (C) 1997-2020 Sam Lantinga <slouken@libsdl.org>

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the authors be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.
*/

#ifndef SDL_thread_h_
#define SDL_thread_h_

/**
 *  \file SDL_thread.h
 *
 *  Header for the SDL thread management routines.
 */

#include "SDL_stdinc.h"
#include "SDL_error.h"

/* Thread synchronization primitives */
#include "SDL_atomic.h"
#include "SDL_mutex.h"

#include "begin_code.h"
/* Set up for C function definitions, even when using C++ */
#ifdef __cplusplus
extern "C" {
#endif

/* The SDL thread structure, defined in SDL_thread.c */
struct SDL_Thread;
typedef struct SDL_Thread SDL_Thread;

/* The SDL thread ID */
typedef unsigned long SDL_threadID;

/* Thread local storage ID, 0 is the invalid ID */
typedef unsigned int SDL_TLSID;

/**
 *  The SDL thread priority.
 *
 *  SDL will make system changes as necessary in order to apply the thread priority.
 *  Code which attempts to control thread state related to priority should be aware
 *  that calling SDL_SetThreadPriority may alter such state.
 *  SDL_HINT_THREAD_PRIORITY_POLICY can be used to control aspects of this behavior.
 *
 *  \note On many systems you require special privileges to set high or time critical priority.
 */
typedef enum {
    SDL_THREAD_PRIORITY_LOW,
    SDL_THREAD_PRIORITY_NORMAL,
    SDL_THREAD_PRIORITY_HIGH,
    SDL_THREAD_PRIORITY_TIME_CRITICAL
} SDL_ThreadPriority;

/**
 *  The function passed to SDL_CreateThread().
 *  It is passed a void* user context parameter and returns an int.
 */
typedef int (SDLCALL * SDL_ThreadFunction) (void *data);

#if defined(__WIN32__)
/**
 *  \file SDL_thread.h
 *
 *  We compile SDL into a DLL. This means, that it's the DLL which
 *  creates a new thread for the calling process with the SDL_CreateThread()
 *  API. There is a problem with this, that only the RTL of the SDL2.DLL will
 *  be initialized for those threads, and not the RTL of the calling
 *  application!
 *
 *  To solve this, we make a little hack here.
 *
 *  We'll always use the caller's _beginthread() and _endthread() APIs to
 *  start a new thread. This way, if it's the SDL2.DLL which uses this API,
 *  then the RTL of SDL2.DLL will be used to create the new thread, and if it's
 *  the application, then the RTL of the application will be used.
 *
 *  So, in short:
 *  Always use the _beginthread() and _endthread() of the calling runtime
 *  library!
 */
#define SDL_PASSED_BEGINTHREAD_ENDTHREAD
#include <process.h> /* _beginthreadex() and _endthreadex() */

typedef uintptr_t (__cdecl * pfnSDL_CurrentBeginThread)
                   (void *, unsigned, unsigned (__stdcall *func)(void *),
                    void * /*arg*/, unsigned, unsigned * /* threadID */);
typedef void (__cdecl * pfnSDL_CurrentEndThread) (unsigned code);

#ifndef SDL_beginthread
#define SDL_beginthread _beginthreadex
#endif
#ifndef SDL_endthread
#define SDL_endthread _endthreadex
#endif

/**
 *  Create a thread.
 */
extern DECLSPEC SDL_Thread *SDLCALL
SDL_CreateThread(SDL_ThreadFunction fn, const char *name, void *data,
                 pfnSDL_CurrentBeginThread pfnBeginThread,
                 pfnSDL_CurrentEndThread pfnEndThread);

extern DECLSPEC SDL_Thread *SDLCALL
SDL_CreateThreadWithStackSize(int (SDLCALL * fn) (void *),
                 const char *name, const size_t stacksize, void *data,
                 pfnSDL_CurrentBeginThread pfnBeginThread,
                 pfnSDL_CurrentEndThread pfnEndThread);


/**
 *  Create a thread.
 */
#if defined(SDL_CreateThread) && SDL_DYNAMIC_API
#undef SDL_CreateThread
#define SDL_CreateThread(fn, name, data) SDL_CreateThread_REAL(fn, name, data, (pfnSDL_CurrentBeginThread)SDL_beginthread, (pfnSDL_CurrentEndThread)SDL_endthread)
#undef SDL_CreateThreadWithStackSize
#define SDL_CreateThreadWithStackSize(fn, name, stacksize, data) SDL_CreateThreadWithStackSize_REAL(fn, name, stacksize, data, (pfnSDL_CurrentBeginThread)SDL_beginthread, (pfnSDL_CurrentEndThread)SDL_endthread)
#else
#define SDL_CreateThread(fn, name, data) SDL_CreateThread(fn, name, data, (pfnSDL_CurrentBeginThread)SDL_beginthread, (pfnSDL_CurrentEndThread)SDL_endthread)
#define SDL_CreateThreadWithStackSize(fn, name, stacksize, data) SDL_CreateThreadWithStackSize(fn, name, data, (pfnSDL_CurrentBeginThread)_beginthreadex, (pfnSDL_CurrentEndThread)SDL_endthread)
#endif

#elif defined(__OS2__)
/*
 * just like the windows case above:  We compile SDL2
 * into a dll with Watcom's runtime statically linked.
 */
#define SDL_PASSED_BEGINTHREAD_ENDTHREAD

#ifndef __EMX__
#include <process.h>
#else
#include <stdlib.h>
#endif

typedef int (*pfnSDL_CurrentBeginThread)(void (*func)(void *), void *, unsigned, void * /*arg*/);
typedef void (*pfnSDL_CurrentEndThread)(void);

#ifndef SDL_beginthread
#define SDL_beginthread _beginthread
#endif
#ifndef SDL_endthread
#define SDL_endthread _endthread
#endif

extern DECLSPEC SDL_Thread *SDLCALL
SDL_CreateThread(SDL_ThreadFunction fn, const char *name, void *data,
                 pfnSDL_CurrentBeginThread pfnBeginThread,
                 pfnSDL_CurrentEndThread pfnEndThread);
extern DECLSPEC SDL_Thread *SDLCALL
SDL_CreateThreadWithStackSize(SDL_ThreadFunction fn, const char *name, const size_t stacksize, void *data,
                 pfnSDL_CurrentBeginThread pfnBeginThread,
                 pfnSDL_CurrentEndThread pfnEndThread);

#if defined(SDL_CreateThread) && SDL_DYNAMIC_API
#undef SDL_CreateThread
#define SDL_CreateThread(fn, name, data) SDL_CreateThread_REAL(fn, name, data, (pfnSDL_CurrentBeginThread)SDL_beginthread, (pfnSDL_CurrentEndThread)SDL_endthread)
#undef SDL_CreateThreadWithStackSize
#define SDL_CreateThreadWithStackSize(fn, name, stacksize, data) SDL_CreateThreadWithStackSize_REAL(fn, name, data, (pfnSDL_CurrentBeginThread)SDL_beginthread, (pfnSDL_CurrentEndThread)SDL_endthread)
#else
#define SDL_CreateThread(fn, name, data) SDL_CreateThread(fn, name, data, (pfnSDL_CurrentBeginThread)SDL_beginthread, (pfnSDL_CurrentEndThread)SDL_endthread)
#define SDL_CreateThreadWithStackSize(fn, name, stacksize, data) SDL_CreateThreadWithStackSize(fn, name, stacksize, data, (pfnSDL_CurrentBeginThread)SDL_beginthread, (pfnSDL_CurrentEndThread)SDL_endthread)
#endif

#else

/**
 *  Create a thread with a default stack size.
 *
 *  This is equivalent to calling:
 *  SDL_CreateThreadWithStackSize(fn, name, 0, data);
 */
extern DECLSPEC SDL_Thread *SDLCALL
SDL_CreateThread(SDL_ThreadFunction fn, const char *name, void *data);

/**
 *  Create a thread.
 *
 *   Thread naming is a little complicated: Most systems have very small
 *    limits for the string length (Haiku has 32 bytes, Linux currently has 16,
 *    Visual C++ 6.0 has nine!), and possibly other arbitrary rules. You'll
 *    have to see what happens with your system's debugger. The name should be
 *    UTF-8 (but using the naming limits of C identifiers is a better bet).
 *   There are no requirements for thread naming conventions, so long as the
 *    string is null-terminated UTF-8, but these guidelines are helpful in
 *    choosing a name:
 *
 *    http://stackoverflow.com/questions/149932/naming-conventions-for-threads
 *
 *   If a system imposes requirements, SDL will try to munge the string for
 *    it (truncate, etc), but the original string contents will be available
 *    from SDL_GetThreadName().
 *
 *   The size (in bytes) of the new stack can be specified. Zero means "use
 *    the system default" which might be wildly different between platforms
 *    (x86 Linux generally defaults to eight megabytes, an embedded device
 *    might be a few kilobytes instead).
 *
 *   In SDL 2.1, stacksize will be folded into the original SDL_CreateThread
 *    function.
 */
extern DECLSPEC SDL_Thread *SDLCALL
SDL_CreateThreadWithStackSize(SDL_ThreadFunction fn, const char *name, const size_t stacksize, void *data);

#endif

/**
 * Get the thread name, as it was specified in SDL_CreateThread().
 *  This function returns a pointer to a UTF-8 string that names the
 *  specified thread, or NULL if it doesn't have a name. This is internal
 *  memory, not to be free()'d by the caller, and remains valid until the
 *  specified thread is cleaned up by SDL_WaitThread().
 */
extern DECLSPEC const char *SDLCALL SDL_GetThreadName(SDL_Thread *thread);

/**
 *  Get the thread identifier for the current thread.
 */
extern DECLSPEC SDL_threadID SDLCALL SDL_ThreadID(void);

/**
 *  Get the thread identifier for the specified thread.
 *
 *  Equivalent to SDL_ThreadID() if the specified thread is NULL.
 */
extern DECLSPEC SDL_threadID SDLCALL SDL_GetThreadID(SDL_Thread * thread);

/**
 *  Set the priority for the current thread
 */
extern DECLSPEC int SDLCALL SDL_SetThreadPriority(SDL_ThreadPriority priority);

/**
 *  Wait for a thread to finish. Threads that haven't been detached will
 *  remain (as a "zombie") until this function cleans them up. Not doing so
 *  is a resource leak.
 *
 *  Once a thread has been cleaned up through this function, the SDL_Thread
 *  that references it becomes invalid and should not be referenced again.
 *  As such, only one thread may call SDL_WaitThread() on another.
 *
 *  The return code for the thread function is placed in the area
 *  pointed to by \c status, if \c status is not NULL.
 *
 *  You may not wait on a thread that has been used in a call to
 *  SDL_DetachThread(). Use either that function or this one, but not
 *  both, or behavior is undefined.
 *
 *  It is safe to pass NULL to this function; it is a no-op.
 */
extern DECLSPEC void SDLCALL SDL_WaitThread(SDL_Thread * thread, int *status);

/**
 *  A thread may be "detached" to signify that it should not remain until
 *  another thread has called SDL_WaitThread() on it. Detaching a thread
 *  is useful for long-running threads that nothing needs to synchronize
 *  with or further manage. When a detached thread is done, it simply
 *  goes away.
 *
 *  There is no way to recover the return code of a detached thread. If you
 *  need this, don't detach the thread and instead use SDL_WaitThread().
 *
 *  Once a thread is detached, you should usually assume the SDL_Thread isn't
 *  safe to reference again, as it will become invalid immediately upon
 *  the detached thread's exit, instead of remaining until someone has called
 *  SDL_WaitThread() to finally clean it up. As such, don't detach the same
 *  thread more than once.
 *
 *  If a thread has already exited when passed to SDL_DetachThread(), it will
 *  stop waiting for a call to SDL_WaitThread() and clean up immediately.
 *  It is not safe to detach a thread that might be used with SDL_WaitThread().
 *
 *  You may not call SDL_WaitThread() on a thread that has been detached.
 *  Use either that function or this one, but not both, or behavior is
 *  undefined.
 *
 *  It is safe to pass NULL to this function; it is a no-op.
 */
extern DECLSPEC void SDLCALL SDL_DetachThread(SDL_Thread * thread);

/**
 *  \brief Create an identifier that is globally visible to all threads but refers to data that is thread-specific.
 *
 *  \return The newly created thread local storage identifier, or 0 on error
 *
 *  \code
 *  static SDL_SpinLock tls_lock;
 *  static SDL_TLSID thread_local_storage;
 * 
 *  void SetMyThreadData(void *value)
 *  {
 *      if (!thread_local_storage) {
 *          SDL_AtomicLock(&tls_lock);
 *          if (!thread_local_storage) {
 *              thread_local_storage = SDL_TLSCreate();
 *          }
 *          SDL_AtomicUnlock(&tls_lock);
 *      }
 *      SDL_TLSSet(thread_local_storage, value, 0);
 *  }
 *  
 *  void *GetMyThreadData(void)
 *  {
 *      return SDL_TLSGet(thread_local_storage);
 *  }
 *  \endcode
 *
 *  \sa SDL_TLSGet()
 *  \sa SDL_TLSSet()
 */
extern DECLSPEC SDL_TLSID SDLCALL SDL_TLSCreate(void);

/**
 *  \brief Get the value associated with a thread local storage ID for the current thread.
 *
 *  \param id The thread local storage ID
 *
 *  \return The value associated with the ID for the current thread, or NULL if no value has been set.
 *
 *  \sa SDL_TLSCreate()
 *  \sa SDL_TLSSet()
 */
extern DECLSPEC void * SDLCALL SDL_TLSGet(SDL_TLSID id);

/**
 *  \brief Set the value associated with a thread local storage ID for the current thread.
 *
 *  \param id The thread local storage ID
 *  \param value The value to associate with the ID for the current thread
 *  \param destructor A function called when the thread exits, to free the value.
 *
 *  \return 0 on success, -1 on error
 *
 *  \sa SDL_TLSCreate()
 *  \sa SDL_TLSGet()
 */
extern DECLSPEC int SDLCALL SDL_TLSSet(SDL_TLSID id, const void *value, void (SDLCALL *destructor)(void*));


/* Ends C function definitions when using C++ */
#ifdef __cplusplus
}
#endif
#include "close_code.h"

#endif /* SDL_thread_h_ */

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