multithreading

问题 The Java memory model guarantees a happens-before relationship between an object's construction and finalizer: There is a happens-before edge from the end of a constructor of an object to the start of a finalizer (§12.6) for that object. As well as the constructor and the initialization of final fields: An object is considered to be completely initialized when its constructor finishes. A thread that can only see a reference to an object after that object has been completely initialized is

问题 I have several workers, each holding its own connection to PostgreSQL. The workers manipulate with different tables. The workers handle parallel requests from outside the system. One of the tables being accessed is the table of users. When some information comes, I first need to ensure there is a record for the user in the table. If there is no record, I wish to create one at first. I'm using the following idiom: if [user does not exist] then [create user] The code of [user does not exist] is

问题 I have several workers, each holding its own connection to PostgreSQL. The workers manipulate with different tables. The workers handle parallel requests from outside the system. One of the tables being accessed is the table of users. When some information comes, I first need to ensure there is a record for the user in the table. If there is no record, I wish to create one at first. I'm using the following idiom: if [user does not exist] then [create user] The code of [user does not exist] is

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 Consider multiple threads are trying to access critical section, what will happen one thread that occurs Exception inside a synchronized block it having wait() and notify() to accrue and release lock. 回答1: The synchronization monitor will be released: "If execution of the body is ever completed, either normally or abruptly, an unlock action is automatically performed on that same monitor." Java Language Specification 17.1. Synchronization. Other threads will be able to continue synchronizing,

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 Consider multiple threads are trying to access critical section, what will happen one thread that occurs Exception inside a synchronized block it having wait() and notify() to accrue and release lock. 回答1: The synchronization monitor will be released: "If execution of the body is ever completed, either normally or abruptly, an unlock action is automatically performed on that same monitor." Java Language Specification 17.1. Synchronization. Other threads will be able to continue synchronizing,

问题 DispatchQueue.global(qos: .background).async { //This will run on the background queue self.writeValue(tag: GlobalData.WRITE_DATA, data: getDataForWrite(1) ) self.writeValue(tag: GlobalData.WRITE_DATA, data: getDataForWrite(2) ) self.writeValue(tag: GlobalData.WRITE_DATA, data: getDataForWrite(3) ) self.writeValue(tag: GlobalData.WRITE_DATA, data: getDataForWrite(4) ) self.writeValue(tag: GlobalData.WRITE_DATA, data: getDataForWrite(5) ) // ..... DispatchQueue.main.async { //This will run on