Abstract: An HTM-assisted Combining Framework (HCF) may enable multiple (combiner and non-combiner) threads to access a shared data structure concurrently using hardware transactional memory (HTM). As long as a combiner executes in a hardware transaction and ensures that the lock associated with the data structure is available, it may execute concurrently with other threads operating on the data structure. HCF may include attempting to apply operations to a concurrent data structure utilizing HTM and if the HTM attempt fails, utilizing flat combining within HTM transactions. Publication lists may be used to announce operations to be applied to a concurrent data structure. A combiner thread may select a subset of the operations in the publication list and attempt to apply the selected operations using HTM. If the thread fails in these HTM attempts, it may acquire a lock associated with the data structure and apply the selected operations without HTM.

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: 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 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: An HTM-assisted Combining Framework (HCF) may enable multiple (combiner and non-combiner) threads to access a shared data structure concurrently using hardware transactional memory (HTM). As long as a combiner executes in a hardware transaction and ensures that the lock associated with the data structure is available, it may execute concurrently with other threads operating on the data structure. HCF may include attempting to apply operations to a concurrent data structure utilizing HTM and if the HTM attempt fails, utilizing flat combining within HTM transactions. Publication lists may be used to announce operations to be applied to a concurrent data structure. A combiner thread may select a subset of the operations in the publication list and attempt to apply the selected operations using HTM. If the thread fails in these HTM attempts, it may acquire a lock associated with the data structure and apply the selected operations without HTM.

Abstract: Systems and methods are disclosed to improve disaster recovery by implementing a scalable low-loss disaster recovery for a data store. The disaster recovery system enables disaster recovery for a linearizable (e.g., externally consistent) distributed data store. The disaster recovery system also provides for a small lag on the backup site relative to the primary site, thereby reducing the data loss by providing a smaller data loss window compared to traditional disaster recovery techniques. The disaster recovery system implements a timestamp for log records based on a globally synchronized clock. The disaster recovery system also implements a watermark service that updates a global watermark timestamp that a backup node uses to apply log records.

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: Compact and scalable mutual exclusion techniques are implemented for multiple executing threads. A thread may acquire a lock by swapping a pointer to the thread into a tail field of a lock data structure. If the swap operation returned a null value, then the lock is acquired. If the swap operation does not return a null value, then the thread may wait to obtain the lock from a predecessor thread. The thread may wait until a grant field in a data structure for the predecessor thread stores a pointer to the lock, signaling to the thread that the thread may acquire the lock.

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 including multiple processors and memory implements a managed runtime providing a synchronization application programming interface (API) for threads that perform synchronized accesses to shared objects. A standardized header of objects includes a memory word storing an object identifier. To lock the object for synchronized access, the memory word may be converted to store the tail of a linked list of a first-in-first-out synchronization structures for threads waiting to acquire the lock, with the object identifier relocated to the list structure. The list structure may further include a stack of threads waiting on events related to the object, with the synchronization API additionally providing wait, notify and related synchronization operations. Upon determining that no threads hold or desire to hold the lock for the object and that no threads are waiting on events related to the object, the memory word may be restored to contain the object identifier.

Abstract: Systems and methods are disclosed to improve disaster recovery by implementing a scalable low-loss disaster recovery for a data store. The disaster recovery system enables disaster recovery for a linearizable (e.g., externally consistent) distributed data store. The disaster recovery system also provides for a small lag on the backup site relative to the primary site, thereby reducing the data loss by providing a smaller data loss window compared to traditional disaster recovery techniques. The disaster recovery system implements a timestamp for log records based on a globally synchronized clock. The disaster recovery system also implements a watermark service that updates a global watermark timestamp that a backup node uses to apply log records.

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: 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 including multiple processors and memory implements a managed runtime providing a synchronization application programming interface (API) for threads that perform synchronized accesses to shared objects. A standardized header of objects includes a memory word storing an object identifier. To lock the object for synchronized access, the memory word may be converted to store the tail of a linked list of a first-in-first-out synchronization structures for threads waiting to acquire the lock, with the object identifier relocated to the list structure. The list structure may further include a stack of threads waiting on events related to the object, with the synchronization API additionally providing wait, notify and related synchronization operations. Upon determining that no threads hold or desire to hold the lock for the object and that no threads are waiting on events related to the object, the memory word may be restored to contain the object identifier.

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 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 system including one or more processors and persistent, word-addressable memory implements a persistent atomic multi-word compare-and-swap operation. On entry, a list of persistent memory locations of words to be updated, respective expected current values contained the persistent memory locations and respective new values to write to the persistent memory locations are provided. The operation atomically performs the process of comparing the existing contents of the persistent memory locations to the respective current values and, should they match, updating the persistent memory locations with the new values and returning a successful status. Should any of the contents of the persistent memory locations not match a respective current value, the operation returns a failed status. The operation is performed such that the system can recover from any failure or interruption by restoring the list of persistent memory locations.

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.