Efficient object sharing in shared-memory multiprocessors.

摘要

The goal of this work is to facilitate efficient use of concurrent shared objects in asynchronous, shared-memory multiprocessors. Shared objects are usually implemented using locks in such systems. However, lock-based implementations result in substantial inefficiency in multiprogrammed systems, where processes are frequently subject to delays due to preemption. This inefficiency arises because processes can be delayed while holding a lock, thereby delaying other processes that require the lock.;In contrast, lock-free and wait-free implementations guarantee that the delay of one process will not delay another process. We show that lock-free and wait-free implementations for shared objects provide a viable alternative to lock-based ones, and that they can provide a significant performance advantage over lock-based implementations in multiprogrammed systems.;Lock-free and wait-free implementations are notoriously difficult to design and to verify as correct. Universal constructions alleviate this problem by generating lock-free and wait-free shared object implementations using sequential implementations. However, previous universal constructions either require significant creative effort on the part of the programmer for each object, or result in objects that have high space and time overhead due to excessive copying.;We present lock-free and wait-free universal constructions that achieve low space and time overhead for a wide spectrum of important objects, while not placing any extra burden on the object programmer. We also show that the space and time overhead of these constructions can be further reduced by using k-exclusion algorithms to restrict access to the shared object. This approach requires a long-lived renaming algorithm that enables processes to acquire and release names repeatedly. We present several efficient k-exclusion and long-lived renaming algorithms.;Our universal constructions are based on the load-linked and store-conditional synchronization instructions. We give a constant-time, wait-free implementation of load-linked and store-conditional using compare-and-swap, and an implementation of multi-word load-linked and store-conditional instructions using similar one-word instructions. These results allow our algorithms and others to be applied more widely; they can also simplify the design of new algorithms.