4 ms·

I haven’t heard about conditional critical regions before - here’s a interesting set of slides for others: http://www-ist.massey.ac.nz/csnotes/355/lectures/moni

I haven’t heard about conditional critical regions before - here’s a interesting set of slides for others: http://www-ist.massey.ac.nz/csnotes/355/lectures/monitors.pdf http://www-ist.massey.ac.nz/csnotes/355/lectures/monitors.pd... . Seems very closely related to condition variables - except you specify the condition at the lock site rather than via a “trigger” before an unlock. I think Google’s internal Mutex class had a LockWhen(callback) which is a pleasure to work with. Definitely an awesome concept.

Gikoskos 8y ago
IIRC there was at least one language that implemented CCRs natively in its syntax. I want to say it's Ada but I could be wrong. If anyone else knows about it please correct me. To understand it better here's the solution to the producer/consumer problem (from wikipedia), using mutexes and semaphores: mtx buffer_mutex; sem fillCount = 0; sem emptyCount = BUFFER_SIZE; procedure producer() { while (true) { item = produceItem(); down(emptyCount); down(buffer_mutex); putItemIntoBuffer(item); up(buffer_mutex); up(fillCount); } } procedure consumer() { while (true) { down(fillCount); down(buffer_mutex); item = removeItemFromBuffer(); up(buffer_mutex); up(emptyCount); consumeItem(item); } } and the same problem solved using CCRs: int avl = 0; procedure producer() { while (true) { item = produceItem(); region R when (avl < BUFFER_SIZE) { putItemIntoBuffer(item); avl++; } } } procedure consumer() { while (true) { region R when (avl > 0) { item = removeItemFromBuffer(); avl--; } consumeItem(item); } } The most important thing about CCRs is that they are supposed to guarantee fairness, along with mutual exclusion. A well-designed solution uses two binary semaphore queues to achieve this. If anyone wants to see what an implementation looks like here's a small C library I wrote a while ago, to use for some of my own personal projects, and to solve some homework for Uni https://github.com/Gikoskos/libccr https://github.com/Gikoskos/libccr
- okl 8y ago
  > I want to say it's Ada but I could be wrong. Yes, entry barriers: http://www.ada-auth.org/standards/12rm/html/RM-9-5-2.html#S0223 http://www.ada-auth.org/standards/12rm/html/RM-9-5-2.html#S0... The consumer/producer routines (entries) conceptually belong to the object/resource that is operated on (protected object) but are executed by the calling task.

Gikoskos 8y ago

IIRC there was at least one language that implemented CCRs natively in its syntax. I want to say it's Ada but I could be wrong. If anyone else knows about it please correct me. To understand it better here's the solution to the producer/consumer problem (from wikipedia), using mutexes and semaphores: mtx buffer_mutex; sem fillCount = 0; sem emptyCount = BUFFER_SIZE; procedure producer() { while (true) { item = produceItem(); down(emptyCount); down(buffer_mutex); putItemIntoBuffer(item); up(buffer_mutex); up(fillCount); } } procedure consumer() { while (true) { down(fillCount); down(buffer_mutex); item = removeItemFromBuffer(); up(buffer_mutex); up(emptyCount); consumeItem(item); } } and the same problem solved using CCRs: int avl = 0; procedure producer() { while (true) { item = produceItem(); region R when (avl < BUFFER_SIZE) { putItemIntoBuffer(item); avl++; } } } procedure consumer() { while (true) { region R when (avl > 0) { item = removeItemFromBuffer(); avl--; } consumeItem(item); } } The most important thing about CCRs is that they are supposed to guarantee fairness, along with mutual exclusion. A well-designed solution uses two binary semaphore queues to achieve this. If anyone wants to see what an implementation looks like here's a small C library I wrote a while ago, to use for some of my own personal projects, and to solve some homework for Uni https://github.com/Gikoskos/libccr https://github.com/Gikoskos/libccr

okl 8y ago
> I want to say it's Ada but I could be wrong. Yes, entry barriers: http://www.ada-auth.org/standards/12rm/html/RM-9-5-2.html#S0223 http://www.ada-auth.org/standards/12rm/html/RM-9-5-2.html#S0... The consumer/producer routines (entries) conceptually belong to the object/resource that is operated on (protected object) but are executed by the calling task.