Sample that uses condition variables.
Conditional variables generally use certain combinations of the following values.
Follow the steps below to wait to be notified from other threads.
Follow the steps below to notify other threads.
The even and odd threads signal each other to continue the process in this sample.
using nlib_ns::threading::ScopedLock;
using nlib_ns::threading::UniqueLock;
using nlib_ns::threading::CondVar;
using nlib_ns::threading::SimpleCriticalSection;
using nlib_ns::threading::Thread;
const int NUM_THREADS = 6;
Thread g_Th[NUM_THREADS];
struct CondVarState {
CondVar cond;
SimpleCriticalSection lock;
bool flag;
public:
CondVarState() : flag(false) {}
} g_Cond1, g_Cond2;
class ThreadParam {
public:
ThreadParam() : thread_num_(0), is_success_(false), wait_(NULL), signal_(NULL) {}
void Initialize(int num, CondVarState* w, CondVarState* s) {
thread_num_ = num;
wait_ = w;
signal_ = s;
is_success_ = true;
}
void Exec();
static void ThreadFunc(ThreadParam* param) { param->Exec(); }
bool IsSuccessful() { return is_success_; }
private:
int thread_num_;
bool is_success_;
CondVarState* wait_;
CondVarState* signal_;
};
void ThreadParam::Exec() {
{
UniqueLock<SimpleCriticalSection> lock(wait_->lock);
while (!wait_->flag) {
errno_t e = wait_->cond.Wait(lock);
is_success_ = false;
return;
}
nlib_printf(
" Thread %d may be notified and acquires lock\n", thread_num_);
}
nlib_printf(
" Thread %d is notified, and do its own job\n", thread_num_);
wait_->flag = false;
}
{
ScopedLock<SimpleCriticalSection> lock(signal_->lock);
signal_->flag = true;
signal_->cond.NotifyAll();
}
}
bool CondVarDemo() {
ThreadParam param[NUM_THREADS];
for (int i = 0; i < NUM_THREADS; ++i) {
if (i % 2 == 0) {
param[i].Initialize(i, &g_Cond1, &g_Cond2);
e = g_Th[i].Start(ThreadParam::ThreadFunc, ¶m[i]);
} else {
param[i].Initialize(i, &g_Cond2, &g_Cond1);
e = g_Th[i].Start(ThreadParam::ThreadFunc, ¶m[i]);
}
}
g_Cond1.lock.lock();
g_Cond1.flag = true;
g_Cond1.cond.NotifyAll();
g_Cond1.lock.unlock();
for (int i = 0; i < NUM_THREADS; ++i) {
e = g_Th[i].Join();
}
for (int i = 0; i < NUM_THREADS; ++i) {
if (!param[i].IsSuccessful()) return false;
}
return true;
}
static bool SampleMain(int, char**) { return CondVarDemo(); }
NLIB_MAINFUNC