Sync Readers Writers
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/***************************************** SyncReadersWriters.h Copyright (c) 2017 David Feng Distributed under the MIT License. *****************************************/ #ifndef SYNC_READERS_WRITERS_H #define SYNC_READERS_WRITERS_H #include <boost/thread/thread.hpp> #include <boost/thread/condition.hpp> #include <boost/thread/mutex.hpp> #include <iostream> #include <string> #include <map> #include <set> #include <boost/function.hpp> #include <deque> #include <queue> #include <boost/shared_ptr.hpp> #include <boost/regex.hpp> #include "Semaphore.h" #include "ThreadMgr.h" /* The readers writers problem http://en.wikipedia.org/wiki/Readers-writers_problem 1. The first readers-writers problem (readers-preference): no reader shall be kept waiting if the shared resource is currently opened for reading 2. The second readers-writers problem (writers-preference): no writer, once added to the queue, shall be kept waiting longer than absolutely necessary 3. The third readers-writers problem (fair readers writers): no thread shall be allowed to starve; that is, the operation of obtaining a lock on the shared resource will always terminate in a bounded amount of time (Note that the solution can only satisfy the condition that "no thread shall be allowed to starve" if and only if semaphores preserve first-in first-out ordering when blocking and releasing threads) */ namespace SyncReadersWriters { class PreferReader //1. simplest { public: explicit PreferReader(const std::string & s) : m_s(s) , m_semaphoreResource(1), m_semaphoreRC(1), m_readCount(0) { } std::string Read() { m_semaphoreRC.Wait();//works like a mutex that protects m_readCount among multiple readers { ++m_readCount; if (m_readCount == 1)//check if you are the first reader thread m_semaphoreResource.Wait();//make first reader thread (and all its successive reader threads) mutual exclusive to any writer thread in the resource critical section. (resource critical section starts) } m_semaphoreRC.Signal(); std::string res = m_s; std::ostringstream oss; oss << "[" << boost::this_thread::get_id() << "]"; std::cout << oss.str(); m_semaphoreRC.Wait();//works like a mutex that protects m_readCount among multiple readers { --m_readCount; if (m_readCount == 0)//check if you are the last reader thread m_semaphoreResource.Signal();//(resource critical section ends) } m_semaphoreRC.Signal(); return res; } void Write(const std::string & s) { m_semaphoreResource.Wait();//(resource critical section starts) { m_s = s; std::ostringstream oss; oss << "<" << boost::this_thread::get_id() << ">"; std::cout << oss.str(); } m_semaphoreResource.Signal();//(resource critical section ends) } private: std::string m_s; Semaphore m_semaphoreResource;//between both reader and writer threads Semaphore m_semaphoreRC;//between reader threads int m_readCount; }; class PreferWriter //3. hardest: adding m_semaphoreWC, m_semaphoreReader { public: explicit PreferWriter(const std::string & s) : m_s(s) , m_semaphoreShared(1), m_semaphoreResource(1) , m_semaphoreRC(1), m_readCount(0) , m_semaphoreWC(1), m_writeCount(0) , m_semaphoreReader(1) { } std::string Read() { m_semaphoreReader.Wait(); { m_semaphoreShared.Wait(); { m_semaphoreRC.Wait(); { ++m_readCount; if (m_readCount == 1)//check if you are the first reader thread m_semaphoreResource.Wait();//make first reader thread (and all its successive reader threads) mutual exclusive to any writer thread in the resource critical section. (resource critical section starts) } m_semaphoreRC.Signal(); } m_semaphoreShared.Signal(); } m_semaphoreReader.Signal(); std::string res = m_s; std::ostringstream oss; oss << "[" << boost::this_thread::get_id() << "]"; std::cout << oss.str(); m_semaphoreRC.Wait(); { --m_readCount; if (m_readCount == 0)//check if you are the last reader thread m_semaphoreResource.Signal();//(resource critical section ends) } m_semaphoreRC.Signal(); return res; } void Write(const std::string & s) { m_semaphoreWC.Wait(); { ++m_writeCount; if (m_writeCount == 1)//check if you are the first writer thread m_semaphoreShared.Wait();//->make first writer thread (and all its successive writer threads) mutual exclusive to any reader thread in the m_semaphoreReader critical section (hold m_semaphoreReader critical section) } m_semaphoreWC.Signal(); m_semaphoreResource.Wait();//(resource critical section starts) { m_s = s; std::ostringstream oss; oss << "<" << boost::this_thread::get_id() << ">"; std::cout << oss.str(); } m_semaphoreResource.Signal();//(resource critical section ends) m_semaphoreWC.Wait(); { --m_writeCount; if (m_writeCount == 0)//check if you are the last writer thread m_semaphoreShared.Signal();//->(release m_semaphoreReader critical section) } m_semaphoreWC.Signal(); } private: std::string m_s; Semaphore m_semaphoreShared;//between both reader and writer threads Semaphore m_semaphoreResource;//between both reader and writer threads Semaphore m_semaphoreRC;//between reader threads int m_readCount; Semaphore m_semaphoreWC;//between writer threads int m_writeCount; Semaphore m_semaphoreReader;//between reader threads }; class FairReaderWriter //2. medium: adding m_semaphoreShared { public: explicit FairReaderWriter(const std::string & s) : m_s(s) , m_semaphoreShared(1), m_semaphoreResource(1), m_semaphoreRC(1), m_readCount(0) { } std::string Read() { m_semaphoreShared.Wait(); { m_semaphoreRC.Wait(); { ++m_readCount; if (m_readCount == 1)//check if you are the first reader thread m_semaphoreResource.Wait();//make first reader thread (and all its successive reader threads) mutual exclusive to any writer thread in the resource critical section. (resource critical section starts) } m_semaphoreRC.Signal(); } m_semaphoreShared.Signal(); std::string res = m_s; std::ostringstream oss; oss << "[" << boost::this_thread::get_id() << "]"; std::cout << oss.str(); m_semaphoreRC.Wait(); { --m_readCount; if (m_readCount == 0)//check if you are the last reader thread m_semaphoreResource.Signal();//(resource critical section ends) } m_semaphoreRC.Signal(); return res; } void Write(const std::string & s) { m_semaphoreShared.Wait(); { m_semaphoreResource.Wait();//(resource critical section starts) { m_s = s; std::ostringstream oss; oss << "<" << boost::this_thread::get_id() << ">"; std::cout << oss.str(); } m_semaphoreResource.Signal();//(resource critical section ends) } m_semaphoreShared.Signal(); } private: std::string m_s; Semaphore m_semaphoreShared;//between both reader and writer threads Semaphore m_semaphoreResource;//between both reader and writer threads Semaphore m_semaphoreRC;//between reader threads int m_readCount; }; class SimpleReaderWriter { public: explicit SimpleReaderWriter(const std::string & s) : m_s(s), m_sharedMutex() {} ~SimpleReaderWriter() {} std::string Read() { boost::shared_lock<boost::shared_mutex> shared_lock(m_sharedMutex); std::string res = m_s; std::ostringstream oss; oss << "[" << boost::this_thread::get_id() << "]"; std::cout << oss.str(); return res; } void Write(const std::string & s) { boost::unique_lock<boost::shared_mutex> unique_lock(m_sharedMutex); m_s = s; std::ostringstream oss; oss << "<" << boost::this_thread::get_id() << ">"; std::cout << oss.str(); } private: std::string m_s; boost::shared_mutex m_sharedMutex; }; /*the following functions are for test*/ std::string Reader1(boost::shared_ptr<PreferReader> pr) { while (true) { int microsec = rand() % 1000000 + 1; boost::this_thread::sleep(boost::posix_time::microseconds(microsec)); pr->Read(); } return ""; } std::string Writer1(boost::shared_ptr<PreferReader> pr) { while (true) { int microsec = rand() % 1000000 + 1; boost::this_thread::sleep(boost::posix_time::microseconds(microsec)); pr->Write(""); } return ""; } std::string Reader2(boost::shared_ptr<PreferWriter> pw) { while (true) { int microsec = rand() % 1000000 + 1; boost::this_thread::sleep(boost::posix_time::microseconds(microsec)); pw->Read(); } return ""; } std::string Writer2(boost::shared_ptr<PreferWriter> pw) { while (true) { int microsec = rand() % 1000000 + 1; boost::this_thread::sleep(boost::posix_time::microseconds(microsec)); pw->Write(""); } return ""; } std::string Reader3(boost::shared_ptr<FairReaderWriter> frw) { while (true) { int microsec = rand() % 1000000 + 1; boost::this_thread::sleep(boost::posix_time::microseconds(microsec)); frw->Read(); } return ""; } std::string Writer3(boost::shared_ptr<FairReaderWriter> frw) { while (true) { int microsec = rand() % 1000000 + 1; boost::this_thread::sleep(boost::posix_time::microseconds(microsec)); frw->Write(""); } return ""; } std::string Reader4(boost::shared_ptr<SimpleReaderWriter> srw) { while (true) { int microsec = rand() % 1000000 + 1; boost::this_thread::sleep(boost::posix_time::microseconds(microsec)); srw->Read(); } return ""; } std::string Writer4(boost::shared_ptr<SimpleReaderWriter> srw) { while (true) { int microsec = rand() % 1000000 + 1; boost::this_thread::sleep(boost::posix_time::microseconds(microsec)); srw->Write(""); } return ""; } void Test() { { std::cout << "Test SyncReadersWriters PreferReader:" << std::endl; boost::shared_ptr<PreferReader> pr(new PreferReader("")); thread_mgr::ThreadMgr m; system("pause"); for (int i = 0; i < 60; ++i) { if (i & 1) m.Dispatch(std::bind(Reader1, pr)); else m.Dispatch(std::bind(Writer1, pr)); } system("pause"); } { std::cout << "Test SyncReadersWriters PreferWriter:" << std::endl; boost::shared_ptr<PreferWriter> pw(new PreferWriter("")); thread_mgr::ThreadMgr m; system("pause"); for (int i = 0; i < 60; ++i) { if (i & 1) m.Dispatch(std::bind(Reader2, pw)); else m.Dispatch(std::bind(Writer2, pw)); } system("pause"); } { std::cout << "Test SyncReadersWriters FairReaderWriter:" << std::endl; boost::shared_ptr<FairReaderWriter> frw(new FairReaderWriter("")); thread_mgr::ThreadMgr m; system("pause"); for (int i = 0; i < 60; ++i) { if (i & 1) m.Dispatch(std::bind(Reader3, frw)); else m.Dispatch(std::bind(Writer3, frw)); } system("pause"); } { std::cout << "Test SyncReadersWriters SimpleReaderWriter:" << std::endl; boost::shared_ptr<SimpleReaderWriter> srw(new SimpleReaderWriter("")); thread_mgr::ThreadMgr m; system("pause"); for (int i = 0; i < 60; ++i) { if (i & 1) m.Dispatch(std::bind(Reader4, srw)); else m.Dispatch(std::bind(Writer4, srw)); } system("pause"); } } } #endif |