This paper presents a new efficient programming toolchain for message-passing parallel algorithms which can fully ensure, for any typable programs and for any execution path, deadlock-freedom, communication safety and global progress through a static checking. The methodology is embodied as a multiparty session-based programming environment for C and its runtime libraries, which we call Session C. Programming starts from specifying a global protocol for a target parallel algorithm, using a protocol description language. From this global protocol, the projection algorithm generates endpoint protocols, based on which each endpoint C program is designed and implemented with a small number of concise session primitives. The endpoint protocol can further be refined to a more optimised protocol through subtyping for asynchronous communication, preserving original safety guarantees. The underlying theory can ensure that the complexity of the toolchain stays in polynomial time against the size of programs. We apply this framework to representative parallel algorithms with complex communication topologies. The benchmark results show that Session C performs competitively against MPI.