locking

问题 I'm new to linux kernel development and wonder how wait_event/wait_event_interruptible interacts with other locking primitives in the kernel. I'm used to C++ std::condition_variable::wait and want to achieve something similar in the kernel. I have a queue of receive buffers which are filled using DMA transfers. The list is protected using a spin lock. Finished buffers are added by the DMA finished soft IRQ. I created a character device which allows reading of the finished buffers. So far this

问题 Is there any way to work with sessions without locking on ASP.Net MVC site ? Session lock mechanism leads many problems; When your site slow down little bit, users are start to hit "F5" on the keyboard. When they do this, requests are starting to wait each other. All those requests are hanging on IIS at " RequestAcquireState " state for session module. If a user made a simultaneous requests this will happen. Because session module in IIS and default session provider (Or generally custom ones)

问题 I have the following problem: I'm using Redis with NodeJS together via mranney's driver and my NodeJS webserver is retrieving some data from Redis, doing some operations on it and saving it back to the Redis. But this operation (call it X) may take a while so multiple users can fire it at the same time on the same resources. So if a user A fires X and user B fires X at the same time I want user A to finish the job and then user B to get the (processed) data and do X. In the meantime user B

问题 We have a table in MySQL using InnoDB, and we are using a transaction isolation level of read uncommitted. Why does setting @x as shown acquire a lock? mysql> set @x = (select userID from users limit 1); Query OK, 0 rows affected (0.02 sec) mysql> Trying to update this table from another prompt results in a timeout error: mysql> update users set userID = 1; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction 回答1: For what it's worth, this locking is not limited to READ

问题 We have a table in MySQL using InnoDB, and we are using a transaction isolation level of read uncommitted. Why does setting @x as shown acquire a lock? mysql> set @x = (select userID from users limit 1); Query OK, 0 rows affected (0.02 sec) mysql> Trying to update this table from another prompt results in a timeout error: mysql> update users set userID = 1; ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction 回答1: For what it's worth, this locking is not limited to READ

问题 After executing the below code, create table t(id int primary key); insert into t values (5),(10); -- session 1 start transaction; select * from t where id > 8 for share; -- session 2 start transaction; insert into t values(6); -- is blocked the output of select * from performance_schema.data_locks is: +--------+---------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+----------------

问题 I am using Qt5 on Windows 7. In my current project I open a binary file in order to populate it with data coming from a TCP socket. Normally, after the file is populated, I close it and another application will read this binary file for further processing. Well, the problem is: The writing operation takes about 4-5 seconds (or even more) so I need to find a way to prevent the other application from reading from the binary file until the file is completely populated ... Here below is the code

问题 I have questions about TMREWSync: Is it possible to upgrade Read lock to Write lock without unlocking? Don't understand what I should do if BeginWrite returns false? 回答1: Yes, TMREWSync supports lock upgrades. Use it like: BeginRead ... BeginWrite ... EndWrite ... EndRead . Source code in System.SysUtils states: The function result of BeginWrite indicates whether another thread got the write lock while the current thread was waiting for the write lock. Return value of True means that the

问题 The way Lock interface with class Reentrant(true) lock works is that it uses BlockingQueue to store Threads that want to acquire the lock . In that way thread that 'came first, go out first'-FIFO. All clear about that. But where do 'unfair locks' go, or ReentrantLock(false). What is their internal implementation? How does OS decide which thread now to pick? And most importantly are now these threads also stored in a queue or where? (they must be somewhere) 回答1: The class ReentrantLock does

问题 The way Lock interface with class Reentrant(true) lock works is that it uses BlockingQueue to store Threads that want to acquire the lock . In that way thread that 'came first, go out first'-FIFO. All clear about that. But where do 'unfair locks' go, or ReentrantLock(false). What is their internal implementation? How does OS decide which thread now to pick? And most importantly are now these threads also stored in a queue or where? (they must be somewhere) 回答1: The class ReentrantLock does