Section: New Results

Parallel and Distributed Verification

Participants : Hubert Garavel, Radu Mateescu, Wendelin Serwe.

For distributed verification, CADP provides the PBG format, which implements the theoretical concept of Partitioned LTS introduced in [46] and provides a unified access to an LTS distributed over a set of remote machines. The PBG format is equipped with the DISTRIBUTOR and PBG_MERGE (previously called BCG_MERGE [45] ) tools, which perform the distributed generation of a partitioned LTS and the conversion of a partitioned LTS represented in the PBG format into a monolithic LTS stored in a BCG file.

To facilitate the manipulation of partitioned LTSs, CADP provides the PBG_CP, PBG_MV, and PBG_RM tools for copying, moving, and removing PBG files, maintaining consistency during these operations. The PBG_INFO tool provides several functionalities to inspect PBG files, such as checking consistency (i.e., existence and readability of all fragment files), calculating the size (number of states and transitions) of the corresponding LTS, displaying the list of labels, and concatenating remote log files (this is useful, e.g., to understand the reason why a PBG generation fails, and to compute global statistics about CPU and memory usage by the worker processes).

In 2012, in addition to correcting two bugs in DISTRIBUTOR and several bugs in the CAESAR_NETWORK_1 communication library used by the distributed verification tools, we also improved these tools as follows:

• We enhanced DISTRIBUTOR to support more than 256 distributed processes.

• We enhanced CAESAR_NETWORK_1 with a debugging facility, which enables traces of all distributed processes to be generated.

• We enhanced the graphical monitor of DISTRIBUTOR with the option of sorting the labels alphabetically, which facilitates their visual inspection.

• We extended PBG_INFO to enable the display of all labels in a partitioned LTS.

We also developed a prototype tool, named PBG_OPEN, which is an OPEN/CAESAR-compliant compiler for the PBG format, enabling the use of all CADP on-the-fly verification tools on a partitioned LTS. The main advantage of PBG_OPEN is that it can use the memory of several machines to store the transition relation of a partitioned LTS. Therefore, PBG_OPEN can explore on-the-fly large partitioned LTSs that could not be explored using other tool combinations. To reduce the amount of communications, PBG_OPEN can use a cache to store already encountered states, together with their outgoing transitions.

We experimented all these tools on the Grid'5000 computing infrastructure [35] using up to 512 distributed processes. These experiments confirmed the good scalability of our distributed LTS manipulation approach. A paper describing this work has been published in an international conference [12] .