![]() ![]() Like many locks across the system, Old River is showing its age and is in need of attention. At present, 30 percent of the Mississippi River’s flow is diverted to the Atchafalaya, which also receives the total inflow of both the Red and Ouachita rivers. In short, the complex is designed to prevent the Mississippi River from changing course to the much steeper Atchafalaya River and abandoning its current course. Hydroelectric Station was completed in 1990. The lock is one of the structures that make up the Old River Control Complex, which also includes the Low Sill Control Structure, the Auxiliary Structure and the Overbank Structure. Old River Lock-located just upriver of the Red River Landing and across the river from Angola, La.-was completed in December 1962 and opened to navigation on March 15, 1963. “The closure is scheduled to start on 15 August 2022 and end on 13 November 2022.” “Old River will be totally closed to navigation for the entire dewatering, and no traffic will be able to pass,” said Ricky Boyett, public affairs chief for the New Orleans District. The first and longest closure will occur at Old River Lock, which is set to close this summer. Release-Acquire ordering, cppreference.The New Orleans and Vicksburg Engineer Districts have a pair of lock closures scheduled for this summer and fall that will temporarily disrupt navigation on both the Red and Ouachita rivers.It was the base foundation for DPDK’s rte_ring. Kip Macy implemented a buffer ring for FreeBSD. From the thread safety point of view, they should not be necessary but they may be there for some reason. In the FreeBSD queue the push () and pop () are wrapped with critical_enter () and critical_exit (). Uint32_t push ( struct queue_t * q, uint32_t * data, uint32_t len ) Open questions The full code can be found in the loki library. Single-consumer single-producer queue (buggy version) Now, the trick is in how to move those pointers atomically. The consumer does something similar: moving the consumer’s head reserves the entries to read so other readers will not pop the same data and the consumer’s tail serves as a stop-marker for the writers. Only when the producer finishes, she will move forward her tail, commiting the change and allowing the readers to proceed. The producer moves her head to reserve the space so other writers will begin to write starting from that point.Īt the same time the consumer will not forward beyond the producer’s tail. Reserve-Commitīoth the producer and the consumer need their own head and tail. The key to resolve this is to have two heads and two tails. The problem is that the write and the move of the head is not a single atomic action. Keep reading.Ĭhanging the order doesn’t fix the problem: a producer may move the head before writing, trying to reserve the space but now a consumer may forward the tail before the data was actually written reading entries that are empty. We cannot longer guarantee that the head was moved after writing the data even if the code say so. You may think that this cannot happen because we have only one producer.Īnd you are correct except for the memory reorders. In the first case we say that the queue is full in the second, the queue is empty.īut if we want to make the queue thread safe without using locks we need to make the push and the pop atomic.Īnd here is the problem: if a producer store the data and later moves the head, another producer will see the old head in between and store her data in the same place overwriting the first one. When head and tail pointers are the same there is not ambiguity. The pointers serve as stop-markers: the producer will not write if the head points to an entry that is immediately before the entry pointed by the tail the consumer will not read if the tail and the head are pointing to the same entry.Įmpty queue. Other implementations do not waste this entry. One entry is always left empty to differentiate a full queue from an empty queue. When a producer pushes a new data to the queue, she moves forward the head and writes the data meanwhile the consumer reads the data and moves forward the tail.įull queue. In a traditional queue we have two pointers: the head, that points to the next free entry to write and the tail, which points to the next entry ready to be read. A multi-producer multi-consumer queue is described in the second part. In this first part will analyse and implement a lock-free single-producer single-consumer queue. While implementing a bounded queue or ring buffer in a single-thread universe is relatively easy, doing the same when you have two threads, the implementation of a lock-free queue is more challenging. ![]() Lock-Free Queue - Part I The Book of Gehn ![]()
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