Context-bounded verification of thread pools

Thread pooling is a common programming idiom in which a fixed set of worker threads are maintained to execute tasks concurrently. The workers repeatedly pick tasks and execute them to completion. Each task is sequential, with possibly recursive code, and tasks communicate over shared memory. Executing a task can lead to more new tasks being spawned. We consider the safety verification problem for thread-pooled programs. We parameterize the problem with two parameters: the size of the thread pool as well as the number of context switches for each task. The size of the thread pool determines the number of workers running concurrently. The number of context switches determines how many times a worker can be swapped out while executing a single task---like many verification problems for multithreaded recursive programs, the context bounding is important for decidability. We show that the safety verification problem for thread-pooled, context-bounded, Boolean programs is EXPSPACE-complete, even if the size of the thread pool and the context bound are given in binary. Our main result, the EXPSPACE upper bound, is derived using a sequence of new succinct encoding techniques of independent language-theoretic interest. In particular, we show a polynomial-time construction of downward closures of languages accepted by succinct pushdown automata as doubly succinct nondeterministic finite automata. While there are explicit doubly exponential lower bounds on the size of nondeterministic finite automata accepting the downward closure, our result shows these automata can be compressed. We show that thread pooling significantly reduces computational power: in contrast, if only the context bound is provided in binary, but there is no thread pooling, the safety verification problem becomes 3EXPSPACE-complete. Given the high complexity lower bounds of related problems involving binary parameters, the relatively low complexity of safety verification with thread-pooling comes as a surprise.

Nondeterministic Syntactic Complexity

We introduce a new measure on regular languages: their nondeterministic syntactic complexity. It is the least degree of any extension of the ‘canonical boolean representation’ of the syntactic monoid. Equivalently, it is the least number of states of any subatomic nondeterministic acceptor. It turns out that essentially all previous structural work on nondeterministic state-minimality computes this measure. Our approach rests on an algebraic interpretation of nondeterministic finite automata as deterministic finite automata endowed with semilattice structure. Crucially, the latter form a self-dual category.

Implementasi Finite State Automata Dalam Siklus Pembelajaran Magister Ilmu Komputer STMIK Nusa Mandiri

Menyelesaikan Pendidikan Magister Ilmu Komputer pada STMIK Nusa Mandiri dalam waktu 4 semester merupakan harapan setiap mahasiswa. Untuk dapat lulus tepat waktu setiap mahasiswa wajib memenuhi semua persyaratan yang telah ditentukan oleh pihak kampus. Dalam tiap semester terdapat berbagai kegiatan diluar kegiatan belajar mengajar yang wajib diikuti oleh mahasiswa. Kegiatan tersebut meliputi Seminar, Workshop, dan Tes TOEFL. Hal-hal tersebut seringkali tidak diketahui mahasiswa sehingga tidak lulus mata kuliah tertentu. Apabila seorang mahasiswa dinyatakan tidak lulus mata kuliah tertentu maka diwajibkan untuk mengulang di semester berikutnya. Mengulang mata kuliah akan menambah pengeluaran dan tentunya menambah waktu belajar sehingga tidak dapat lulus tepat waktu sesuai yang diharapkan. Pada paper ini akan membahas tentang bagaimana Finite State Automata (FSA) jenis Nondeterministic Finite Automata (NFA) dapat diimplementasikan dalam siklus pembelajaran Magister Ilmu Komputer pada STMIK Nusa Mandiri. Dengan diterapkan metode ini diharapkan dapat membantu mahasiswa dalam pemenuhan persyaratan untuk mencapai kelulusan