Abstract

In this paper we describe restartable atomic sequences, an optimistic mechanism for implementing simple atomic operations (such as Test-And-Set) on a uniprocessor. A thread that is suspended within a restartable atomic sequence is resumed by the operating system at the beginning of the sequence, rather than at the point of suspension. This guarantees that the thread eventually executes the sequence atomically. A restartable atomic sequence has signi cantly less overhead than other software-based synchronization mechanisms, such askernel emulation or software reservation. Consequently, it is an attractive alternative for use on uniprocessors that do not support atomic operations. Even on processors that do support atomic operations in hardware, restartable atomic sequences can have lower overhead. We describe di erent implementations of restartable atomic sequences for the Mach 3.0 and Taos operating systems. These systems ' thread management packages

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