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Lock in C By Shobha Shivakumar. Popular Course in this category. Course Price View Course. Free Software Development Course. In a situation where a resource is changed infrequently, a ReaderWriterLock provides better throughput than a simple one-at-a-time lock, such as Monitor. ReaderWriterLock works best where most accesses are reads, while writes are infrequent and of short duration. Multiple readers alternate with single writers, so that neither readers nor writers are blocked for long periods.
Holding reader locks or writer locks for long periods will starve other threads. For best performance, consider restructuring your application to minimize the duration of writes. A thread can hold a reader lock or a writer lock, but not both at the same time.
Readers and writers are queued separately. When a thread releases the writer lock, all threads waiting in the reader queue at that instant are granted reader locks; when all of those reader locks have been released, the next thread waiting in the writer queue, if any, is granted the writer lock, and so on. In other words, ReaderWriterLock alternates between a collection of readers, and one writer.
While a thread in the writer queue is waiting for active reader locks to be released, threads requesting new reader locks accumulate in the reader queue. Their requests are not granted, even though they could share concurrent access with existing reader-lock holders; this helps protect writers against indefinite blockage by readers.
Most methods for acquiring locks on a ReaderWriterLock accept time-out values. Use time-outs to avoid deadlocks in your application. For example, a thread might acquire the writer lock on one resource and then request a reader lock on a second resource; in the meantime, another thread might acquire the writer lock on the second resource, and request a reader lock on the first.
Unless time-outs are used, the threads deadlock. If the time-out interval expires and the lock request has not been granted, the method returns control to the calling thread by throwing an ApplicationException. A thread can catch this exception and determine what action to take next. Time-outs are expressed in milliseconds. If you use a System. See how the file ends up.
Then remove either one or both of these instructions in order to see how the file ends up. And then you will understand what these two instructions do. Now, to test the program for its safety in accessing a file concurrently, run the program not only once but many times.
But before you do this, add one or more Console. ReadLine and Console. The Console. Each instance will unlock the file when the FileStream is closed.
From the time the FileStream is opened to the time the FileStream is closed, only one instance can access the file, whether for reading, writing or both. Dimitrios Kalemis. I am exactly like Jesus Christ: an atheist and anarchist against society and bad people with influence and power judges, social workers, politicians, priests, and teachers.
Skip to content. How to lock a text file for reading and writing using C Posted on June 23, by Dimitrios Kalemis. Here it is: using System; using System. IO; using System. WriteLine "Sequence begins. Open, FileAccess. ReadWrite, FileShare. The content you requested has been removed.
Ask a question. Quick access. Search related threads. Remove From My Forums. Answered by:. Archived Forums. Visual C. Jayahar Devadhason 0. Sign in to vote. Wednesday, April 22, AM. You can use FileStream. Lock and FileStream. UnLock for locking the file. I'm guessing that the code for your unlock and lock buttons does not have access to the FileStream where you have locked the file?
Do you want to unlock a file that has been locked elsewhere? Marked as answer by D. Wednesday, April 22, PM. FileInfo pathToTheFile ; if! IsReadOnly fileInfo. Best regards, Sergiu.
Thursday, April 23, AM.
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