mutex

问题 In answering another question I wrote a little struct using sync.Map to cache API requests. type PostManager struct { sync.Map } func (pc PostManager) Fetch(id int) Post { post, ok := pc.Load(id) if ok { fmt.Printf("Using cached post %v\n", id) return post.(Post) } fmt.Printf("Fetching post %v\n", id) post = pc.fetchPost(id) pc.Store(id, post) return post.(Post) } Unfortunately, if two goroutines both fetch the same uncached Post at the same time, both will make a request. var postManager

问题 What is the reason for a notified condition variable to re-lock the mutex after being notified. The following piece of code deadlock if unique_lock is not scoped or if mutex is not explicitely unlocked #include <future> #include <mutex> #include <iostream> using namespace std; int main() { std::mutex mtx; std::condition_variable cv; //simulate another working thread sending notification auto as = std::async([&cv](){ std::this_thread::sleep_for(std::chrono::seconds(2)); cv.notify_all();}); /

问题 An example from The Linux Programming Interface : In the producer threads, we would have code such as the following: static pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER; static int avail = 0; /* Code to produce a unit omitted */ s = pthread_mutex_lock(&mtx); if (s != 0) errExitEN(s, "pthread_mutex_lock"); avail++; /* Let consumer know another unit is available */ s = pthread_mutex_unlock(&mtx); if (s != 0) errExitEN(s, "pthread_mutex_unlock"); And in the main (consumer) thread, we could

问题 I use library NModbus4 and create RTU connection. public static IModbusSerialMaster Master { get; set; } Master = ModbusSerialMaster.CreateRtu(SerialPort); I have method GetClient() which return Master and Method Registers() which look like: public static ushort[] Registers(Func<IModbusSerialMaster, ushort[]> action) { ushort[] registers = new ushort[0]; var client = GetClient(); if (client == null) return registers; //mutex.WaitOne(); try { registers = action.Invoke(client); } catch

问题 I was trying to understand memory barrier and came across the below wikipedia link http://en.wikipedia.org/wiki/Memory_barrier This explain the concept well but had thoughts if this is really helpful in system where we have mutex() locking the memory section. Taking the same code as mentioned in wikipedia, will the below approach solve the problem using mutex? [Note: Function names are not specific to any programming language, just used for simplicity sake] Processor #1 mutex_lock(a) while (f

问题 I was trying to understand memory barrier and came across the below wikipedia link http://en.wikipedia.org/wiki/Memory_barrier This explain the concept well but had thoughts if this is really helpful in system where we have mutex() locking the memory section. Taking the same code as mentioned in wikipedia, will the below approach solve the problem using mutex? [Note: Function names are not specific to any programming language, just used for simplicity sake] Processor #1 mutex_lock(a) while (f

问题 What is the difference between shared_lock and shared_mutex.lock_shared() other than that the destructor of shared_lock unlocks the associated mutex? Is a shared_mutex the only mutex class I can use with shared_lock ? Why would someone want to use lock_guard instead of unique_lock ? If I have many threads constantly locking for reading ( shared_lock ) a variable and I have a variable that tries to lock it for writing ( unique_lock ), will this writing thread have a priority over the other

问题 What is the difference between shared_lock and shared_mutex.lock_shared() other than that the destructor of shared_lock unlocks the associated mutex? Is a shared_mutex the only mutex class I can use with shared_lock ? Why would someone want to use lock_guard instead of unique_lock ? If I have many threads constantly locking for reading ( shared_lock ) a variable and I have a variable that tries to lock it for writing ( unique_lock ), will this writing thread have a priority over the other

问题 What is the difference between shared_lock and shared_mutex.lock_shared() other than that the destructor of shared_lock unlocks the associated mutex? Is a shared_mutex the only mutex class I can use with shared_lock ? Why would someone want to use lock_guard instead of unique_lock ? If I have many threads constantly locking for reading ( shared_lock ) a variable and I have a variable that tries to lock it for writing ( unique_lock ), will this writing thread have a priority over the other

问题 What is the difference between shared_lock and shared_mutex.lock_shared() other than that the destructor of shared_lock unlocks the associated mutex? Is a shared_mutex the only mutex class I can use with shared_lock ? Why would someone want to use lock_guard instead of unique_lock ? If I have many threads constantly locking for reading ( shared_lock ) a variable and I have a variable that tries to lock it for writing ( unique_lock ), will this writing thread have a priority over the other