Abstract: A data object has a lock and a condition indicator associated with it. Based at least partly on detecting a first setting of the condition indicator, a reader stores an indication that the reader has obtained read access to the data object in an element of a readers structure and reads the data object without acquiring the lock. A writer detects the first setting and replaces it with a second setting, indicating that the lock is to be acquired by readers before reading the data object. Prior to performing a write on the data object, the writer verifies that one or more elements of the readers structure have been cleared.

Abstract: A first data accessor acquires a lock associated with a critical section. The first data accessor initiates a help session associated with a first operation of the critical section. In the help session, a second data accessor (which has not acquired the first lock) performs one or more sub-operations of the first operation. The first data accessor releases the lock after at least the first operation has been completed.

Abstract: A computer comprising one or more processors and memory may implement multiple threads that perform a lock operation using a data structure comprising an allocation field and a grant field. Upon entry to a lock operation, a thread allocates a ticket by atomically copying a ticket value contained in the allocation field and incrementing the allocation field. The thread compares the allocated ticket to the grant field. If they are unequal, the thread determines a number of waiting threads. If the number is above the threshold, the thread enters a long term wait operation comprising determining a location for long term wait value and waiting on changes to that value. If the number is below the threshold or the long term wait operation is complete, the thread waits for the grant value to equal the ticket to indicate that the lock is allocated.

Abstract: Parameter permutation is performed for federated learning to train a machine learning model. Parameter permutation is performed by client systems of a federated machine learning system on updated parameters of a machine learning model that have been updated as part of training using local training data. An intra-model shuffling technique is performed at the client systems according to a shuffling pattern. Then, the encoded parameters are provided to an aggregation server using Private Information Retrieval (PIR) queries generated according to the shuffling pattern.

Abstract: Transactional Lock Elision allows hardware transactions to execute unmodified critical sections protected by the same lock concurrently, by subscribing to the lock and verifying that it is available before committing the transaction. A “lazy subscription” optimization, which delays lock subscription, can potentially cause behavior that cannot occur when the critical sections are executed under the lock. Hardware extensions may provide mechanisms to ensure that lazy subscriptions are safe (e.g., that they result in correct behavior). Prior to executing a critical section transactionally, its lock and subscription code may be identified (e.g., by writing their locations to special registers). Prior to committing the transaction, the thread executing the critical section may verify that the correct lock was correctly subscribed to. If not, or if locations identified by the special registers have been modified, the transaction may be aborted.

Abstract: A first data accessor acquires a lock associated with a critical section. The first data accessor initiates a help session associated with a first operation of the critical section. In the help session, a second data accessor (which has not acquired the first lock) performs one or more sub-operations of the first operation. The first data accessor releases the lock after at least the first operation has been completed.

Abstract: NUMA-aware reader-writer locks may leverage lock cohorting techniques that introduce a synthetic level into the lock hierarchy (e.g., one whose nodes do not correspond to the system topology). The synthetic level may include a global reader lock and a global writer lock. A writer thread may acquire a node-level writer lock, then the global writer lock, and then the top-level lock, after which it may access a critical section protected by the lock. The writer may release the lock (if an upper bound on consecutive writers has been met), or may pass the lock to another writer (on the same node or a different node, according to a fairness policy). A reader may acquire the global reader lock (whether or not node-level reader locks are present), and then the top-level lock. However, readers may only hold these locks long enough to increment reader counts associated with them.

Abstract: Transactional Lock Elision allows hardware transactions to execute unmodified critical sections protected by the same lock concurrently, by subscribing to the lock and verifying that it is available before committing the transaction. A “lazy subscription” optimization, which delays lock subscription, can potentially cause behavior that cannot occur when the critical sections are executed under the lock. Hardware extensions may provide mechanisms to ensure that lazy subscriptions are safe (e.g., that they result in correct behavior). Prior to executing a critical section transactionally, its lock and subscription code may be identified (e.g., by writing their locations to special registers). Prior to committing the transaction, the thread executing the critical section may verify that the correct lock was correctly subscribed to. If not, or if locations identified by the special registers have been modified, the transaction may be aborted.

Abstract: Generic Concurrency Restriction (GCR) may divide a set of threads waiting to acquire a lock into two sets: an active set currently able to contend for the lock, and a passive set waiting for an opportunity to join the active set and contend for the lock. The number of threads in the active set may be limited to a predefined maximum or even a single thread. Generic Concurrency Restriction may be implemented as a wrapper around an existing lock implementation. Generic Concurrency Restriction may, in some embodiments, be unfair (e.g., to some threads) over the short term, but may improve the overall throughput of the underlying multithreaded application via passivation of a portion of the waiting threads.

Abstract: NUMA-aware reader-writer locks may leverage lock cohorting techniques that introduce a synthetic level into the lock hierarchy (e.g., one whose nodes do not correspond to the system topology). The synthetic level may include a global reader lock and a global writer lock. A writer thread may acquire a node-level writer lock, then the global writer lock, and then the top-level lock, after which it may access a critical section protected by the lock. The writer may release the lock (if an upper bound on consecutive writers has been met), or may pass the lock to another writer (on the same node or a different node, according to a fairness policy). A reader may acquire the global reader lock (whether or not node-level reader locks are present), and then the top-level lock. However, readers may only hold these locks long enough to increment reader counts associated with them.

Abstract: Generic Concurrency Restriction (GCR) may divide a set of threads waiting to acquire a lock into two sets: an active set currently able to contend for the lock, and a passive set waiting for an opportunity to join the active set and contend for the lock. The number of threads in the active set may be limited to a predefined maximum or even a single thread. Generic Concurrency Restriction may be implemented as a wrapper around an existing lock implementation. Generic Concurrency Restriction may, in some embodiments, be unfair (e.g., to some threads) over the short term, but may improve the overall throughput of the underlying multithreaded application via passivation of a portion of the waiting threads.

Abstract: A computer comprising one or more processors and memory may implement multiple threads performing mutually exclusive lock acquisition operations on disjoint ranges of a shared resource each using atomic compare and swap (CAS) operations. A linked list of currently locked ranges is maintained and, upon entry to a lock acquisition operation, a thread waits for all locked ranges overlapping the desired range to be released then inserts a descriptor for the desired range into the linked list using a single CAS operation. To release a locked range, a thread executes a single fetch and add (FAA) operation. The operation may be extended to support simultaneous exclusive and non-exclusive access by allowing overlapping ranges to be locked for non-exclusive access and by performing an additional validation after locking to provide conflict resolution should a conflict be detected.

Abstract: A data object has a lock and a condition indicator associated with it. Based at least partly on detecting a first setting of the condition indicator, a reader stores an indication that the reader has obtained read access to the data object in an element of a readers structure and reads the data object without acquiring the lock. A writer detects the first setting and replaces it with a second setting, indicating that the lock is to be acquired by readers before reading the data object. Prior to performing a write on the data object, the writer verifies that one or more elements of the readers structure have been cleared.

Abstract: A computer comprising one or more processors and memory may implement multiple threads performing mutually exclusive lock acquisition operations on disjoint ranges of a shared resource each using atomic compare and swap (CAS) operations. A linked list of currently locked ranges is maintained and, upon entry to a lock acquisition operation, a thread waits for all locked ranges overlapping the desired range to be released then inserts a descriptor for the desired range into the linked list using a single CAS operation. To release a locked range, a thread executes a single fetch and add (FAA) operation. The operation may be extended to support simultaneous exclusive and non-exclusive access by allowing overlapping ranges to be locked for non-exclusive access and by performing an additional validation after locking to provide conflict resolution should a conflict be detected.

Abstract: A data object has a lock and a condition indicator associated with it. Based at least partly on detecting a first setting of the condition indicator, a reader stores an indication that the reader has obtained read access to the data object in an element of a readers structure and reads the data object without acquiring the lock. A writer detects the first setting and replaces it with a second setting, indicating that the lock is to be acquired by readers before reading the data object. Prior to performing a write on the data object, the writer verifies that one or more elements of the readers structure have been cleared.

Abstract: A computer comprising one or more processors and memory may implement multiple threads that perform a lock operation using a data structure comprising an allocation field and a grant field. Upon entry to a lock operation, a thread allocates a ticket by atomically copying a ticket value contained in the allocation field and incrementing the allocation field. The thread compares the allocated ticket to the grant field. If they are unequal, the thread determines a number of waiting threads. If the number is above the threshold, the thread enters a long term wait operation comprising determining a location for long term wait value and waiting on changes to that value. If the number is below the threshold or the long term wait operation is complete, the thread waits for the grant value to equal the ticket to indicate that the lock is allocated.

Abstract: A computer comprising multiple processors and non-uniform memory implements multiple threads that perform a lock operation using a shared lock structure that includes a pointer to a tail of a first-in-first-out (FIFO) queue of threads waiting to acquire the lock. To acquire the lock, a thread allocates and appends a data structure to the FIFO queue. The lock is released by selecting and notifying a waiting thread to which control is transferred, with the thread selected executing on the same processor socket as the thread controlling the lock. A secondary queue of threads is managed for threads deferred during the selection process and maintained within the data structures of the waiting threads such that no memory is required within the lock structure. If no threads executing on the same processor socket are waiting for the lock, entries in the secondary queue are transferred to the FIFO queue preserving FIFO order.

Abstract: Concurrent threads may be synchronized at the level of the memory words they access rather than at the level of the lock that protects the execution of critical sections. Each lock may be associated with an array of flags and each flag may indicate ownership of certain memory words. A pessimistic thread may set flags corresponding to memory words it is accessing in the critical section, while an optimistic thread may read the corresponding flag before any memory access to ensure that the flag is not set and that therefore the associated memory word is not being accessed by the other thread. Thus, optimistic threads that do not have conflicts with the pessimistic thread may not have to wait for the pessimistic thread to release the lock before proceeding.

Abstract: A remove operation and an add-to-front operation may be currently performed with respect to nodes in an Least Recently Used (LRU) queue. A remove operation for a node may proceed if a lock can be obtained on the node to be removed and a predecessor node. During the remove operation, an add-to-front operation may proceed if a lock can be obtained on a dummy node that precedes the current front node of the LRU queue.

Abstract: A computer comprising one or more processors and memory may implement multiple threads that perform a lock operation using a data structure comprising an allocation field and a grant field. Upon entry to a lock operation, a thread allocates a ticket by atomically copying a ticket value contained in the allocation field and incrementing the allocation field. The thread compares the allocated ticket to the grant field. If they are unequal, the thread determines a number of waiting threads. If the number is above the threshold, the thread enters a long term wait operation comprising determining a location for long term wait value and waiting on changes to that value. If the number is below the threshold or the long term wait operation is complete, the thread waits for the grant value to equal the ticket to indicate that the lock is allocated.