readers and writers problem 读者写者问题 写者优先 C++实现

参考http://en.wikipedia.org/wiki/Readers-writers_problem

第二类读者写者问题，写优先

#include <cstdio>#include <Windows.h>#include <ctime>int readcount, writecount;HANDLE mutex_1; // 限制readcountHANDLE mutex_2; // 限制writecountHANDLE mutex_3; // 限制rHANDLE r; // 有没有readerHANDLE w; // 有没有writer/*能够并发地读，不能并发地写，写的时候不能读，写优先*/DWORD WINAPI reader_thread(void *param);DWORD WINAPI writer_thread(void *param);DWORD WINAPI reader_thread(void * param){int my_id = *(int *)param;printf("%dth reader come\n", my_id);WaitForSingleObject(mutex_3, INFINITE);WaitForSingleObject(r,INFINITE);WaitForSingleObject(mutex_1, INFINITE);readcount += 1;if(readcount == 1) WaitForSingleObject(w, INFINITE);//只要有reader已经在read，就不让一个write去写ReleaseMutex(mutex_1);ReleaseMutex(r);ReleaseMutex(mutex_3);/*reading*/printf("%dth reader is doing reading\n", my_id);Sleep(2000);printf("%dth reader finish reading\n", my_id);WaitForSingleObject(mutex_1, INFINITE);readcount -= 1;if (readcount == 0) ReleaseMutex(w);ReleaseMutex(mutex_1);return 1;}DWORD WINAPI writer_thread(void *param){int my_id = *(int *)param;printf("%dth writer come\n", my_id);WaitForSingleObject(mutex_2, INFINITE);writecount += 1;if(writecount == 1) WaitForSingleObject(r, INFINITE);//只要有writer存在，就reader在后面等待ReleaseMutex(mutex_2);WaitForSingleObject(w, INFINITE);printf("%dth writer is writing\n", my_id);Sleep(2000);printf("%dth writer finish writing\n", my_id);WaitForSingleObject(mutex_2, INFINITE);writecount -= 1;if(writecount == 0)ReleaseMutex(r);ReleaseMutex(mutex_2);return 1;}#define NUM 100000int reader_id,writer_id;int temp_r[NUM], temp_w[NUM];void gen(){HANDLE h;if(rand()%2==0) // 产生reader{reader_id++;temp_r[reader_id] = reader_id;h = CreateThread(NULL, 0, reader_thread, (void *)(&temp_r[reader_id]), 0, NULL);}else // 产生writer{writer_id++;temp_w[writer_id] = writer_id;h = CreateThread(NULL, 0, writer_thread, (void *)(&temp_w[writer_id]), 0, NULL);}}int main (){mutex_1 = CreateMutex(NULL, FALSE, L"mutex_1");mutex_2 = CreateMutex(NULL, FALSE, L"mutex_2");mutex_3 = CreateMutex(NULL, FALSE, L"mutex_3");r = CreateMutex(NULL, FALSE, L"r");w = CreateMutex(NULL, FALSE, L"w");srand(time(NULL));while(reader_id<NUM && writer_id<NUM){if(rand()%2 == 0){gen();}if(rand()%3 == 0){gen();}if(rand()%3 == 0){gen();}Sleep(3000);}return 0;}