SDL  2.0
SDL_syscond.cpp File Reference
#include "../../SDL_internal.h"
#include "SDL_thread.h"
#include <chrono>
#include <condition_variable>
#include <ratio>
#include <system_error>
#include "SDL_sysmutex_c.h"
+ Include dependency graph for SDL_syscond.cpp:

Go to the source code of this file.

Data Structures

struct  SDL_cond
 

Functions

SDL_condSDL_CreateCond (void)
 
void SDL_DestroyCond (SDL_cond *cond)
 
int SDL_CondSignal (SDL_cond *cond)
 
int SDL_CondBroadcast (SDL_cond *cond)
 
int SDL_CondWaitTimeout (SDL_cond *cond, SDL_mutex *mutex, Uint32 ms)
 
int SDL_CondWait (SDL_cond *cond, SDL_mutex *mutex)
 

Function Documentation

◆ SDL_CondBroadcast()

int SDL_CondBroadcast ( SDL_cond cond)

Restart all threads that are waiting on the condition variable.

Returns
0 or -1 on error.

Definition at line 84 of file SDL_syscond.cpp.

References SDL_cond::cpp_cond, and SDL_SetError.

85 {
86  if (!cond) {
87  SDL_SetError("Passed a NULL condition variable");
88  return -1;
89  }
90 
91  cond->cpp_cond.notify_all();
92  return 0;
93 }
#define SDL_SetError
std::condition_variable_any cpp_cond
Definition: SDL_syscond.cpp:36

◆ SDL_CondSignal()

int SDL_CondSignal ( SDL_cond cond)

Restart one of the threads that are waiting on the condition variable.

Returns
0 or -1 on error.

Definition at line 70 of file SDL_syscond.cpp.

References SDL_cond::cpp_cond, and SDL_SetError.

71 {
72  if (!cond) {
73  SDL_SetError("Passed a NULL condition variable");
74  return -1;
75  }
76 
77  cond->cpp_cond.notify_one();
78  return 0;
79 }
#define SDL_SetError
std::condition_variable_any cpp_cond
Definition: SDL_syscond.cpp:36

◆ SDL_CondWait()

int SDL_CondWait ( SDL_cond cond,
SDL_mutex mutex 
)

Wait on the condition variable, unlocking the provided mutex.

Warning
The mutex must be locked before entering this function!

The mutex is re-locked once the condition variable is signaled.

Returns
0 when it is signaled, or -1 on error.

Definition at line 159 of file SDL_syscond.cpp.

References SDL_CondWaitTimeout(), and SDL_MUTEX_MAXWAIT.

160 {
161  return SDL_CondWaitTimeout(cond, mutex, SDL_MUTEX_MAXWAIT);
162 }
int SDL_CondWaitTimeout(SDL_cond *cond, SDL_mutex *mutex, Uint32 ms)
#define SDL_MUTEX_MAXWAIT
Definition: SDL_mutex.h:49

◆ SDL_CondWaitTimeout()

int SDL_CondWaitTimeout ( SDL_cond cond,
SDL_mutex mutex,
Uint32  ms 
)

Waits for at most ms milliseconds, and returns 0 if the condition variable is signaled, SDL_MUTEX_TIMEDOUT if the condition is not signaled in the allotted time, and -1 on error.

Warning
On some platforms this function is implemented by looping with a delay of 1 ms, and so should be avoided if possible.

Definition at line 118 of file SDL_syscond.cpp.

References SDL_cond::cpp_cond, SDL_mutex::cpp_mutex, SDL_MUTEX_MAXWAIT, SDL_MUTEX_TIMEDOUT, and SDL_SetError.

Referenced by SDL_CondWait().

119 {
120  if (!cond) {
121  SDL_SetError("Passed a NULL condition variable");
122  return -1;
123  }
124 
125  if (!mutex) {
126  SDL_SetError("Passed a NULL mutex variable");
127  return -1;
128  }
129 
130  try {
131  std::unique_lock<std::recursive_mutex> cpp_lock(mutex->cpp_mutex, std::adopt_lock_t());
132  if (ms == SDL_MUTEX_MAXWAIT) {
133  cond->cpp_cond.wait(
134  cpp_lock
135  );
136  cpp_lock.release();
137  return 0;
138  } else {
139  auto wait_result = cond->cpp_cond.wait_for(
140  cpp_lock,
141  std::chrono::duration<Uint32, std::milli>(ms)
142  );
143  cpp_lock.release();
144  if (wait_result == std::cv_status::timeout) {
145  return SDL_MUTEX_TIMEDOUT;
146  } else {
147  return 0;
148  }
149  }
150  } catch (std::system_error & ex) {
151  SDL_SetError("unable to wait on a C++ condition variable: code=%d; %s", ex.code(), ex.what());
152  return -1;
153  }
154 }
std::recursive_mutex cpp_mutex
#define SDL_MUTEX_TIMEDOUT
Definition: SDL_mutex.h:44
#define SDL_MUTEX_MAXWAIT
Definition: SDL_mutex.h:49
#define SDL_SetError
GLbitfield GLuint64 timeout
std::condition_variable_any cpp_cond
Definition: SDL_syscond.cpp:36

◆ SDL_CreateCond()

SDL_cond* SDL_CreateCond ( void  )

Create a condition variable.

Typical use of condition variables:

Thread A: SDL_LockMutex(lock); while ( ! condition ) { SDL_CondWait(cond, lock); } SDL_UnlockMutex(lock);

Thread B: SDL_LockMutex(lock); ... condition = true; ... SDL_CondSignal(cond); SDL_UnlockMutex(lock);

There is some discussion whether to signal the condition variable with the mutex locked or not. There is some potential performance benefit to unlocking first on some platforms, but there are some potential race conditions depending on how your code is structured.

In general it's safer to signal the condition variable while the mutex is locked.

Definition at line 42 of file SDL_syscond.cpp.

References SDL_cond::cond, NULL, SDL_OutOfMemory, and SDL_SetError.

43 {
44  /* Allocate and initialize the condition variable */
45  try {
46  SDL_cond * cond = new SDL_cond;
47  return cond;
48  } catch (std::system_error & ex) {
49  SDL_SetError("unable to create a C++ condition variable: code=%d; %s", ex.code(), ex.what());
50  return NULL;
51  } catch (std::bad_alloc &) {
53  return NULL;
54  }
55 }
#define NULL
Definition: begin_code.h:164
#define SDL_OutOfMemory()
Definition: SDL_error.h:52
#define SDL_SetError

◆ SDL_DestroyCond()

void SDL_DestroyCond ( SDL_cond cond)

Destroy a condition variable.

Definition at line 60 of file SDL_syscond.cpp.

References SDL_cond::cond.

61 {
62  if (cond) {
63  delete cond;
64  }
65 }