synchronization

My web application returns a file from the filesystem. These files are dynamic, so I have no way to know the names o how many of them will there be. When this file doesn't exist, the application creates it from the database. I want to avoid that two different threads recreate the same file at the same time, or that a thread try to return the file while other thread is creating it. Also, I don't want to get a lock over a element that is common for all the files. Therefore I should lock the file just when I'm creating it. So I want to lock a file till its recreation is complete, if other thread

I'm looking to implement data synchronization between servers and distributed clients. The data source on the server is mysql with django on top. The client can vary. Updates can take place on either client or server, and the connection between server and client is not reliable (eg. changes can be made on a disconnected cell phone, should get sync'd when the cell phone has a connection again). S. Lott suggests using a version control design pattern in this question , which makes sense. I'm wondering if there are any existing packages / implementations of this I can use. Or, should I directly

I have the following C++ code where I make use of the Critical Section object : EnterCriticalSection(&cs); // code that may throw an exception LeaveCriticalSection(&cs); How can I ensure that the LeaveCriticalSection function is called even if an exception is thrown? Just write a guard utilizing the destructor for clean up: struct Guard { CriticalSection& cs; Guard(CriticalSection& cs) : cs(cs) { EnterCriticalSection(cs); } ~Guard() { LeaveCriticalSection(cs); } Guard(const Guard&) = delete; Guard& operator = (const Guard&) = delete; }; Usage: void f() { Guard guard(cs); ... } marcinj Use RAII

I have a piece of code that can be executed by multiple threads that needs to perform an I/O-bound operation in order to initialize a shared resource that is stored in a ConcurrentMap . I need to make this code thread safe and avoid unnecessary calls to initialize the shared resource. Here's the buggy code: private ConcurrentMap<String, Resource> map; // ..... String key = "somekey"; Resource resource; if (map.containsKey(key)) { resource = map.get(key); } else { resource = getResource(key); // I/O-bound, expensive operation map.put(key, resource); } With the above code, multiple threads may

I have a trigger function: CREATE OR REPLACE FUNCTION "trigger_deleteUsers"() RETURNS trigger AS $BODY$ BEGIN INSERT INTO "DeletedEntities" ("uuidKey", "dateCreated", "dateModified", "dateSynced", "username", "entityName") VALUES (OLD."uuidKey", OLD."dateCreated", OLD."dateModified", "dateSynced", OLD."username", 'Users'); RETURN NULL; END; $BODY$ LANGUAGE plpgsql; CREATE TRIGGER "deleteUsers" AFTER DELETE ON "Users" FOR EACH ROW EXECUTE PROCEDURE "trigger_deleteUsers"(); This works for the table "Users". Every time I delete a row from the "Users" table the database inserts a row with (

I have a problem with the MS C compiler reordering certain statements, critical in a multithreading context, at high levels of optimization. I want to know how to force ordering in specific places while still using high levels of optimization. (At low levels of optimization, this compiler does not reorder statements) The following code: ChunkT* plog2sizeChunk=... SET_BUSY(plog2sizeChunk->pPoolAndBusyFlag); // set "busy" bit on this chunk of storage x = plog2sizeChunk->pNext; produces this: 0040130F 8B 5A 08 mov ebx,dword ptr [edx+8] 00401312 83 22 FE and dword ptr [edx],0FFFFFFFEh in which the