locking

问题 I know what the following code does and I know why it is a broken code for synchronization as it has only one conditional variable while we need two but I don't know how to provide a sequence of interleaving threads for showing it doesn't work. Can you show why this code doesn't work with an example? 1 cond_t cond = PTHREAD_COND_INITIALIZER; 2 mutex_t mutex=PTHREAD_MUTEX_INITIALIZER;; 3 4 void *producer(void *arg) { 5 int i; 6 for (i = 0; i < loops; i++) { 7 Pthread_mutex_lock(&mutex); 8

问题 There is a student whose type attribute is 4 and the minimum value for type attribute can be 1. In postgres In session 1, I exclusively lock and update a row in the student table: BEGIN; LOCK TABLE students IN ROW EXCLUSIVE MODE; SELECT * FROM students WHERE id = 122 FOR UPDATE; UPDATE students SET type = 1 WHERE id = 122; END; In session 2 I concurrently run: UPDATE students SET type = type - 1 WHERE id = 122; The result I get is an exception, i.e student's type can't be lower than 1 in

问题 There is a student whose type attribute is 4 and the minimum value for type attribute can be 1. In postgres In session 1, I exclusively lock and update a row in the student table: BEGIN; LOCK TABLE students IN ROW EXCLUSIVE MODE; SELECT * FROM students WHERE id = 122 FOR UPDATE; UPDATE students SET type = 1 WHERE id = 122; END; In session 2 I concurrently run: UPDATE students SET type = type - 1 WHERE id = 122; The result I get is an exception, i.e student's type can't be lower than 1 in

问题 I'm a bit wondering about an update i'm making one a big table, do i need to worry about locks. I have a table looking like this: CREATE TABLE "ItemsToProcess"( "id" text, "WorkerInstanceId" text, "ProcessingStartTime" timestamp with time zone, "UpdatedTime" timestamp with time zone, CONSTRAINT "ITP_PK" PRIMARY KEY ("id") )WITH ( OIDS=FALSE ); Initially, this table has ~2.0 million rows in it, and only ID filled in, WorkerInstanceId and the two timestamps are null by default and on the start

问题 How do you look up a default global table locking hint? -- Questions Are there any DMV/DMF (Dynamic Management View/Function) that return such information? And also, is there a way to change the default lock hint? Currently I am adding nolock hint almost everywhere to prevent locks. I'd like to avoid doing so by changing the default lock hint to nolock so that existing stored procedures do not need to change. 回答1: I am not aware of any such global setting. IMHO even should that exist there

问题 BACKGROUND: I use an offset into a file and the Filestream lock/unlock menthods to control read/write access. I am using the following code to test if a lock is currently held on the file try { fs.Lock( RESERVED_BYTE, 1 ); fs.Unlock( RESERVED_BYTE, 1 ); rc = 1; } catch { rc = 0; } QUESTION: My goal is to eliminate the try/catch block. Is there some better way to see if the lock exists? EDIT: Note: This question is not about if the file exists. I already know it does. It is about synchronizing

问题 I had asked question about lock in here and people responded there is no problem in my lock implementation. But i catched problem. Here is same lock implementation and i am getting weird result. I expect to see numbers starts from 1 but it starts from 5.Example is at below. class Program { static object locker = new object(); static void Main(string[] args) { for (int j = 0; j < 100; j++) { (new Thread(new ParameterizedThreadStart(dostuff))).Start(j); } Console.ReadKey(); } static void

问题 Imagine a network of several nix machines. A dedicated node stores files and periodically schedules Task A that modifies these files. Each of the other nodes schedules Task B that syncs ( rsync ) those files to local storage. Task A can take considerable amount of time and the file collection needs to be in a consistent state on all nodes. Thus Task B shouldn't run while Task A is running. A possible solution for this is to use a reader-writer lock. Task A and Task B would put a write and a

问题 I seem to be having an issue with boost::interprocess::file_lock I have process 1 that is essentially boost::interprocess::file_lock test_lock("testfile.csv"); test_lock.lock(); sleep(1000); test_lock.unlock(); When I run a second process while the first process is sleeping, I find that I am still able to read testfile.csv. What's worse, I can even overwrite it. Am I misinterpreting how file_lock works? I was under the impression that calling .lock() gives it exclusive lock over the file and

问题 I have a Problem to find a good concept on locking files in bash, Basically I want to achieve the following: Lock File Read in the data in the file (multiple times) Do stuff with the data. Write new stuff to the file (not necessarily to the end) Unlock that file Doing this with flock seems not possible to me, because the file descriptor will just move once to the end of the file. Also creating a Tempfile fails, because I might overwrite already read lines which is also not possible. Edit: