Dekker’s algorithm is a way of synchronizing two threads around a critical section. It is a dance where thread 1 sets its flag declaring its intent to enter the critical section, then it checks the flag of thread 2. If it is not set, it enters the critical section, if it is set, it resets its flag and backs off. Thread 2 does the same.
Below is my implementation of the algorithm using C++ atomics.
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#include <iostream> #include <atomic> #include <thread> using namespace std; const int COUNT = 10; int main(int argc, char** argv) { atomic_bool f1{false}, f2{false}; auto proc1 = [&]() { for(int i = 0; i < COUNT;) { f1.store(true); if(f2.load() == false) { cout << "T1 in critical section" << endl; ++i; } f1.store(false); } }; auto proc2 = [&]() { for(int i = 0; i < COUNT;) { f2.store(true); if(f1.load() == false) { cout << "T2 in critical section" << endl; ++i; } f2.store(false); } }; thread t1(proc1); thread t2(proc2); t1.join(); t2.join(); return 1; } |
T1 in
Program output.critical section
T2 incritical section
T1 incritical section
T2 incritical section
T2 incritical section
T1 incritical section
T1 incritical section
T2 incritical section
T1 incritical section
T2 incritical section
T1 incritical section
T2 incritical section
T1 incritical section
T2 incritical section
T1 incritical section
T2 incritical section
T1 incritical section
T2 incritical section
T1 incritical section
T2 incritical section
Program ended with exit code: 1
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