locking

问题 So the syntax for select for update is something like SELECT * //1st query FROM test WHERE id = 4 FOR UPDATE; UPDATE test //2nd query SET parent = 100 WHERE id = 4; I am guessing the locking part is the first line. So when the first set of queries executes, I should not be able to select and modify the row with id = 4 (it is primary key by the way). However, I am still able to select row with id = 4 before I update anything, meaning another thread could probably come in and try to select and

问题 I need lock a function from another function in java. In example above, I call slave function to print counter. And I need when that if master function called, all threads which calls slave function must be wait master functions to be ended. How can I do that? int counter = 0; private void slave() { System.out.println(counter); } private void master() { lockSlave(); counter ++; unlockSlave(); } 回答1: Take a look at JDK ReentrantReadWriteLock. private final ReadWriteLock lock = new

问题 I'm reading this link to learn about futex of Linux. Here is something that I don't understand. In order to acquire the lock, an atomic test-and-set instruction (such as cmpxchg()) can be used to test for 0 and set to 1. In this case, the locking thread acquires the lock without involving the kernel (and the kernel has no knowledge that this futex exists). When the next thread attempts to acquire the lock, the test for zero will fail and the kernel needs to be involved. I don't quite

问题 I'm reading this link to learn about futex of Linux. Here is something that I don't understand. In order to acquire the lock, an atomic test-and-set instruction (such as cmpxchg()) can be used to test for 0 and set to 1. In this case, the locking thread acquires the lock without involving the kernel (and the kernel has no knowledge that this futex exists). When the next thread attempts to acquire the lock, the test for zero will fail and the kernel needs to be involved. I don't quite

问题 I'm reading this link to learn about futex of Linux. Here is something that I don't understand. In order to acquire the lock, an atomic test-and-set instruction (such as cmpxchg()) can be used to test for 0 and set to 1. In this case, the locking thread acquires the lock without involving the kernel (and the kernel has no knowledge that this futex exists). When the next thread attempts to acquire the lock, the test for zero will fail and the kernel needs to be involved. I don't quite

问题 I have a stored procedure that is executed by remote clients on an ongoing basis. From reading the docs I am under the impression that with the proper locking techniques I shouldn't need to externally manage these clients and I would be free to have them run as often and as concurrently as they like. This procedure updates and inserts to multiple tables. A skeleton outline of the procedure is below: LOCK TABLE table1 IN EXCLUSIVE MODE; LOOP UPDATE table1 SET "var1"="var1"+1, WHERE "var2"=var2

问题 I have a stored procedure that is executed by remote clients on an ongoing basis. From reading the docs I am under the impression that with the proper locking techniques I shouldn't need to externally manage these clients and I would be free to have them run as often and as concurrently as they like. This procedure updates and inserts to multiple tables. A skeleton outline of the procedure is below: LOCK TABLE table1 IN EXCLUSIVE MODE; LOOP UPDATE table1 SET "var1"="var1"+1, WHERE "var2"=var2

问题 I use a query like this: INSERT INTO table SELECT * FROM table2 t2 JOIN ... ... WHERE table2.date < now() - '1 day'::INTERVAL FOR UPDATE OF t2 SKIP LOCKED ON CONFLICT (...) DO UPDATE SET ... RETURNING *; My question is about FOR UPDATE t2 SKIP LOCKED . Should I use it here? Or will Postgres lock these rows automatically with INSERT SELECT ON CONFLICT till the end of the transaction? My goal is to prevent other apps from (concurrently) capturing rows with the inner SELECT which are already

问题 I am quite not understanding the lock functionality with SELECT FOR UPDATE. Here is what I've tried. CREATE TABLE ACCOUNT_TAB ( ACC_ID int NOT NULL PRIMARY KEY, BALANCE int NOT NULL ); INSERT INTO ACCOUNT_TAB VALUES(1, 100); SELECT * FROM ACCOUNT_TAB FOR UPDATE; SELECT * FROM ACCOUNT_TAB; Both SELECT will retrieve the row, but shouldn't the first query lock the row in the ACCOUNT_TAB table? I have read something about sessions: queries from the same session don't care about the lock. Can I

问题 Using C# running on mono on Linux, notice that below code works well on windows can lock a file across process but not on linux via mono (ubuntu 14.04) new FileStream("myfile.lock",FileMode.OpenOrCreate,FileAccess.ReadWrite,FileShare.None); research from internet, i should be able to do it with advisory lock FileStream.Lock however, it doesn`t work. tested with two processes on ubuntu 14.04, both of them can execute "FileStream.Lock(0, int.MaxValue)". i would expect the later one will fail