Coroutines and events are two common abstractions for writing concurrent programs. Because coroutines are often more convenient, but events more portable and efficient, it is natural to want to translate the former into the latter. CPC is such a source-to-source translator for C programs, based on a partial conversion into continuation-passing style (CPS conversion) of functions annotated as cooperative. In this article, we study the application of the CPC translator to QEMU, an open-source machine emulator which also uses annotated coroutine functions for concurrency. We first propose a new type of annotations to identify functions which never cooperate, and we introduce CoroCheck, a tool for the static analysis and inference of cooperation annotations. Then, we improve the CPC translator, defining CPS conversion as a calling convention for the C language, with support for indirect calls to CPS-converted function through function pointers. Finally, we apply CoroCheck and CPC to QEMU (750 000 lines of C code), fixing hundreds of missing annotations and comparing performance of the translated code with existing implementations of coroutines in QEMU. Our work shows the importance of static annotation checking to prevent actual concurrency bugs, and demonstrates that CPS conversion is a flexible, portable, and efficient compilation technique, even for very large programs written in an imperative language.
Deriving state-machines from a threaded-style code is as old as @cite_38 . Implementations have then been improved in multiple directions: as C preprocessor macros @cite_6 , as source-to-source transformations on C++ @cite_20 or Java @cite_44 programs, as a transformation on JVM bytecode @cite_43 , or as LLVM code blocks and macros based on GCC's nested functions @cite_29 .
@cite_38 @cite_29 @cite_6 @cite_44 @cite_43 @cite_20
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This paper introduces AC, a set of language constructs for composable asynchronous IO in native languages such as C C++. Unlike traditional synchronous IO interfaces, AC lets a thread issue multiple IO requests so that they can be serviced concurrently, and so that long-latency operations can be overlapped with computation. Unlike traditional asynchronous IO interfaces, AC retains a sequential style of programming without requiring code to use multiple threads, and without requiring code to be "stack-ripped" into chains of callbacks. AC provides an "async" statement to identify opportunities for IO operations to be issued concurrently, a "do..finish" block that waits until any enclosed "async" work is complete, and a "cancel" statement that requests cancellation of unfinished IO within an enclosing "do..finish". We give an operational semantics for a core language. We describe and evaluate implementations that are integrated with message passing on the Barrelfish research OS, and integrated with asynchronous file and network IO on Microsoft Windows. We show that AC offers comparable performance to existing C C++ interfaces for asynchronous IO, while providing a simpler programming model. Event-driven programming is a popular model for writing programs for tiny embedded systems and sensor network nodes. While event-driven programming can keep the memory overhead down, it enforces a state machine programming style which makes many programs difficult to write, maintain, and debug. We present a novel programming abstraction called protothreads that makes it possible to write event-driven programs in a thread-like style, with a memory overhead of only two bytes per protothread. We show that protothreads significantly reduce the complexity of a number of widely used programs previously written with event-driven state machines. For the examined programs the majority of the state machines could be entirely removed. In the other cases the number of states and transitions was drastically decreased. With protothreads the number of lines of code was reduced by one third. The execution time overhead of protothreads is on the order of a few processor cycles. The event-driven programming style is pervasive as an efficient method for interacting with the environment. Unfortunately, the event-driven style severely complicates program maintenance and understanding, as it requires each logical flow of control to be fragmented across multiple independent callbacks. We propose tasks as a new programming model for organizing event-driven programs. Tasks are a variant of cooperative multi-threading and allow each logical control flow to be modularized in the traditional manner, including usage of standard control mechanisms like procedures and exceptions. At the same time, by using method annotations, task-based programs can be automatically and modularly translated into efficient event-based code, using a form of continuation passing style (CPS) translation. A linkable scheduler architecture permits tasks to be used in many different contexts. We have instantiated our model as a backward-compatible extension to Java, called TaskJava. We illustrate the benefits of our language through a formalization in an extension to Featherweight Java, and through a case study based on an open-source web server. This paper describes Kilim, a framework that employs a combination of techniques to help create robust, massively concurrent systems in mainstream languages such as Java: (i) ultra-lightweight, cooperatively-scheduled threads (actors), (ii) a message-passing framework (no shared memory, no locks) and (iii) isolation-aware messaging. Isolation is achieved by controlling the shape and ownership of mutable messages --- they must not have internal aliases and can only be owned by a single actor at a time. We demonstrate a static analysis built around isolation type qualifiers to enforce these constraints. Kilim comfortably scales to handle hundreds of thousands of actors and messages on modest hardware. It is fast as well --- task-switching is 1000x faster than Java threads and 60x faster than other lightweight tasking frameworks, and message-passing is 3x faster than Erlang (currently the gold standard for concurrency-orientedprogramming). Tame is a new event-based system for managing concurrency in network applications. Code written with Tame abstractions does not suffer from the "stack-ripping" problem associated with other event libraries. Like threaded code, tamed code uses standard control flow, automatically-managed local variables, and modular interfaces between callers and callees. Tame's implementation consists of C++ libraries and a source-to-source translator; no platform-specific support or compiler modifications are required, and Tame induces little runtime overhead. Experience with Tame in real-world systems, including a popular commercial Web site, suggests it is easy to adopt and deploy.