操作系统同步互斥经典问题——读者写者问题

#include <iostream>#include <mutex>#include <thread>using namespace std;mutex mt, wsem;int readcount = 0;#define READ(a) cout << a << " is reading..." << endl;#define FINISH(a) cout << a << " finished reading." << endl;#define WRITE cout << "writing..." << endl;void P(mutex &mt){    mt.lock();}void V(mutex &mt){    mt.unlock();}// 加入unistd.h出现问题，似乎与thread的兼容性比较差，于是重写void delay(){    int sum=0;    for(int i = 0; i < 10000000; i++)        sum += i}void read(string a){    for(int i = 0; i < 3; i++)    {        P(mt);        readcount++;        if(readcount == 1)            P(wsem);        V(mt);        READ(a);        delay();        P(mt);        readcount--;        FINISH(a);        if(readcount == 0)            V(wsem);        V(mt);    }}void write(){    for(int i = 0; i < 5; i++)    {        P(wsem);        WRITE;        delay();        V(wsem);    }}int main(){    thread reader1(read, "svtter");    thread reader2(read, "sr");    thread reader3(read, "yym");    thread reader4(read, "xiaoniu");    thread writer(write);    reader1.join();    reader2.join();    reader3.join();    reader4.join();    writer.join();    return 0;}

使rsem中只有一个读者在等待，保证了如果有写者，写者优先写。

#include <iostream>#include <mutex>#include <thread>using namespace std;#define READ(a,i) cout << a << i<<" is reading..." << endl;#define FINR(a,i) cout << a << i<<" finished reading." << endl;#define WRITE(a,i) cout << a <<i<<" is writing..." << endl;#define FINW(a, i) cout << a <<i<<" finished writing..." << endl;void P(mutex &mt){    mt.lock();}void V(mutex &mt){    mt.unlock();}// 加入unistd.h出现问题，似乎与thread的兼容性比较差，于是重写void delay(){    int sum=0;    for(int i = 0; i < 10000000; i++)        sum += i;}mutex mr, wsem, rsem, mrc, mwc;int readcount = 0;int writecount = 0;void read(string a){    for(int i = 0; i < 5; i++)    {        P(mr);        P(rsem);        P(mrc);        readcount++;        if(readcount == 1)            P(wsem);        V(mrc);        V(rsem);        V(mr);        READ(a, i);        P(mrc);        FINR(a, i);        readcount--;        if(readcount == 0)            V(wsem);        V(mrc);    }}void write(string a){    for(int i = 0; i < 3; i++)    {        P(mwc);        writecount++;        if(writecount == 1)            P(rsem);        V(mwc);        P(wsem);        WRITE(a, i);        FINW(a, i);        V(wsem);        P(mwc);        writecount--;        if(writecount == 0)            V(rsem);        V(mwc);    }}int main(){    thread reader1(read, "svtter");    thread writer1(write, "sr");    thread writer2(write, "zs");    thread writer3(write, "yym");    reader1.join();    writer1.join();    writer2.join();    writer3.join();    return 0;}