Are there any drawbacks to using semaphores in Java?
One drawback in your code is the starvation for writers. The first reader has acquired writeLock, and so subsequent readers will keep on coming and will not let readCount become 0. So any waiting writers will always wait for writeLock to be released and will eventually starve.
Do you need a readlock semaphore in Java?
The readLock semaphore protects the readCount variable, so the original code is fine. No need for additional mechanisms to make it atomic in this case. There’s no need to use synchronize for readers, as you are acquiring the lock for readCount++ and readCount–. One drawback in your code is the starvation for writers.
How are semaphores used in production and consumer?
This busy-waiting makes already high resource contention worse. But all is not lost. With the help of the OS, we can implement semaphores so that the calling process will block instead of spin in the P () operation and wait for the V () operation to “wake it up” making it runnable again.
Is there such a thing as a blocking semaphore?
The pseudo-code below shows the implementation of such a semaphore, called a blocking semaphore : Please notice that the P ()ing process must atomically become unrunnable and release the mutex. This is becuase of the risk of a lost wakeup .
When to use the readers-writers problem in Java?
The readers-writers problem is used for managing synchronization among various reader and writer process so that there are no problems with the data sets, i.e. no inconsistency is generated. Let’s understand with an example – If two or more than two readers want to access the file at the same point in time there will be no problem.
How are semaphores used to solve the readers problem?
We chose to implement our solution (with readers preference) using semaphores. First some quick (probably skipable) refresh course to (formal) semaphores: Semaphores where first introduced by Dijkstra in 1968, who thought it to be an useful tool for implementing mutual exclusion and for signalling the occurrence of events such as interrupts.