摘要:
One embodiment of the present invention provides a system that implements a hash table that is fully dynamic and lock-free. During a lookup in the hash table the system first uses a hash key to lookup a bucket pointer in a bucket array. Next, the system follows the bucket pointer to a data node within a linked list that contains all of the data nodes in the hash table, wherein the linked list contains only data nodes and at most a constant number of dummy nodes. The system then searches from the data node through the linked list to locate a node that matches the hash key, if one exists.
摘要:
One embodiment of the present invention provides a system that performs operations on a hash table that is fully dynamic and lock-free. This hash table is implemented with a linked list containing data nodes and a bucket array containing bucket pointers, wherein the bucket pointers point to portions of the linked list that function as hash buckets, and wherein the linked list contains only data nodes and no dummy nodes.
摘要:
One embodiment of the present invention provides a system that implements a hash table that is fully dynamic and lock-free. During a lookup in the hash table the system first uses a hash key to lookup a bucket pointer in a bucket array. Next, the system follows the bucket pointer to a data node within a linked list that contains all of the data nodes in the hash table, wherein the linked list contains only data nodes and at most a constant number of dummy nodes. The system then searches from the data node through the linked list to locate a node that matches the hash key, if one exists.
摘要:
One embodiment of the present invention provides a system that supports concurrent accesses to a skip list that is lock-free, which means that the skip list can be simultaneously accessed by multiple processes without requiring the processes to perform locking operations. During a node deletion operation, the system receives reference to a target node to be deleted from the skip list. The system marks a next pointer in the target node to indicate that the target node is deleted, wherein next pointer contains the address of an immediately following node in the skip list. This marking operation does not destroy the address of the immediately following node, and furthermore, the marking operation is performed atomically and thereby without interference from other processes. The system then atomically modifies the next pointer of an immediately preceding node in the skip list to point to an immediately following node in the skip list, instead of pointing to the target node, thereby splicing the target node out of the skip list.
摘要:
A linked-list-based concurrent shared object implementation has been developed that provides non-blocking and linearizable access to the concurrent shared object. In an application of the underlying techniques to a deque, the linked-list-based algorithm allows non-blocking completion of access operations without restricting concurrency in accessing the deque's two ends. The new implementation is based at least in part on a new technique for splitting a pop operation into two steps, marking that a node is about to be deleted, and then deleting it. Once marked, the node logically deleted, and the actual deletion from the list can be deferred. In one realization, actual deletion is performed as part of a next push or pop operation performed at the corresponding end of the deque. An important aspect of the overall technique is synchronization of delete operations when processors detect that there are only marked nodes in the list and attempt to delete one or more of these nodes concurrently from both ends of the deque.
摘要:
We present a methodology for transforming concurrent data structure implementations that depend on garbage collection to equivalent implementations that do not. Assuming the existence of garbage collection makes it easier to design implementations of concurrent data structures, particularly because it eliminates the well-known ABA problem. However, this assumption limits their applicability. Our results demonstrate that, for a significant class of data structures, designers can first tackle the easier problem of an implementation that does depend on garbage collection, and then apply our methodology to achieve a garbage-collection-independent implementation. Our methodology is based on the well-known reference counting technique, and employs the double compare-and-swap operation.
摘要:
A license plate bracket includes a pair of resilient hooks for hooking the bracket to the grille of a vehicle. The hooks, in part, replace conventional hardware such as screws and bolts which are incompatible with the thin plastic ribs found on modern vehicle front grilles. The entire bracket, including the hooks, can be formed as a one-piece plastic molding.
摘要:
A set of structures and techniques are described herein whereby an exemplary concurrent shared object, namely a shared skip list, can be implemented in a lock-free manner. Indeed, we have developed a number of interesting variants of a lock-free shared skip-list, including variants that may be employed to provide a lock-free shared dictionary. In some variants, a key-value dictionary is implemented.
摘要:
The present invention provides a unified grammar for a speech interpreter capable of real-time speech understanding for user applications running on a general purpose microprocessor-based computer. The speech interpreter includes a unified grammar (UG) compiler, a speech recognizer and a natural language (NL) processor. The UG compiler receives a common UG lexicon and unified grammar description, and generates harmonized speech recognition (SR) and NL grammars for the speech recognizer and natural language processor, respectively. The lexicon includes a plurality of UG word entries having predefined characteristics, i.e., features, while the UG description includes a plurality of complex UG rules which define grammatically allowable word sequences. The UG compiler converts the complex UG rules (complex UG rules include augmentations for constraining the UG rules) into permissible SR word sequences and SR simple rules (simple rules do not include any augmentation) for the SR grammar. The SR grammar is a compact representation of the SR word entries corresponding to the UG word entries, permissible SR word sequences and simple SR rules corresponding to the augmentations of the complex UG rules. The NL grammar provides the NL processor with NL patterns enabling the NL processor to extract the meaning of the validated word sequences passed from the speech recognizer.
摘要:
One embodiment of the present invention provides a system that supports inserting or deleting nodes at any location within a doubly-linked list which is lock-free, wherein lock-free means that the doubly-linked list can be simultaneously accessed by multiple processes without requiring the processes to perform locking operations (non-blocking) and furthermore that a finite number of steps performed by a process will guarantee progress by at least one process (lock-free). During operation, the system receives a reference to a target node to be deleted from the doubly-linked list. Next, the system atomically marks a forward pointer in the target node to indicate that the target node is deleted, wherein the forward pointer contains the address of an immediately following node in the doubly-linked list, and wherein the marking operation does not destroy the address of the immediately following node. Additional cleanup steps are then done by this or any other process. The system may also receive a new node which is accessible by only the requesting thread and may then insert the new node into the doubly linked list after a reference node. The system accomplishes this by setting the new node's backward pointer to the reference node and forward pointer to the successor of the reference node. Next, the system atomically changes the forward pointer of the reference node from the successor node to the new node. Additional cleanup steps are then done by this or any other process. An update operation that atomically performs a delete of an old node and an insert of its replacement node is also described.