Fast Serial - Append File I / O Mode Support for Cilk

Apart from resources, such as memory and processors, parallel computations also require file I/O. There exist a number of interesting file I/O modes, depending on the specific application. One particularly interesting file I/O mode is serial-append, described in [5]. In this mode the file output of a parallel computation, executed on any number of processors, is “the same” as the output of the sequential, single processor execution. Cheerio, an implementation of serial-append presented in [5], uses a special formated file where ordering metadata about the parallel execution of the computation is saved together with the actual data. This allows for later reconstruction of the output of the sequential execution. The algorithm described in [5] uses a single mutex-ed counter that allows a worker processor to obtain a new node to write to, when a steal operation occurs in Cilk’s scheduler. Additional locking mechanisms are also performed by Cilk’s Runtime System in order to correctly maintain the order of the structure required by Cheerio. Due to the high overhead of the steal operation this method does not scale up with the number of processors.