The Grace Safe Threading Library

Copyright (c) 2007-13 Emery Berger, University of Massachusetts Amherst.

Emery Berger http://www.cs.umass.edu/~emery

Introduction

Grace is a runtime system for safe and efficient multithreading. Grace replaces the standard pthreads library with a new runtime system that eliminates concurrency errors while maintaining good scalability and high performance. Grace works with unaltered C/C++ programs, requires no compiler support, and runs on standard hardware platforms. Grace can ensure the correctness of otherwise-buggy multithreaded programs, and at the same time, achieve high performance and scalability.

Grace prevents the following errors:

• deadlocks
• race conditions
• atomicity violations
• nondeterministic results

In effect, running with Grace makes a multithreaded program act like each thread is executing sequentially, one after the other. However, Grace can actually execute these threads concurrently, so that the resulting program can scale up.

Grace currently works for multithreaded programs with fork-join parallelism; in other words, programs that divide computation work into a number of threads. Grace provides the highest scalability when these threads are reasonably long-lived and do not modify much data that is shared across the threads.

Building Grace

Just change into the src/ directory and type make gcc-x86.

Grace currently works only on x86-based Linux platforms with the GNU C/C++ compilers.

Using Grace

To use Grace, change the final compile step in your program (the link stage) so that it links with Grace instead of with pthreads.

For example, change this link step:

g++ mycode.cpp -lpthreads -o mycode

to the following:

g++ -Wl,-T grace.ld mycode.cpp -L/grace/install/dir -lgrace -o mycode

where /grace/install/dir should be replaced by wherever you choose to install Grace.

NOTE: Grace does not yet work in 64-bit mode. When compiling code on 64-bit architectures with GNU C++, use the -m32 compiler flag, as in:

g++ -m32 -Wl,-T grace.ld mycode.cpp -L/grace/install/dir -lgrace -o mycode

Limitations

• Grace currently is only supported for 32-bit, x86 platforms; Linux / GNU only.

• Grace can significantly slow down a multithreaded program. Your mileage may vary. Grace will scale perfectly for a program whose threads do not update any data shared across the threads. Detailed experiments measuring the relative effect of different thread lengths (in runtime) and amount of sharing are in our paper, listed below.

• Grace is currently designed to support programs that use multiple threads to speed up computation using fork-join parallelism. In particular, Grace does not currently support threads that "run forever" or that communicate with each other via condition variables. Dthreads, our follow-on project, handles such programs and generally provides higher performance, at the cost of reducing its semantic guarantees (it only guarantees deterministic execution).

More information

Grace's technology consists of three key components:

• a novel virtual memory based software transactional memory system (STM) implemented on top of processes
• an ordering protocol to guarantee sequential program semantics
• an optimized mmap-based heap and global variables that lets processes behave like threads.

For more detailed technical information about Grace, see the following paper:

Grace: Safe Multithreaded Programming for C/C++ Emery D. Berger, Ting Yang, Tongping Liu, and Gene Novark. Proceedings of the 24th ACM SIGPLAN conference on Object Oriented Programming Systems, Languages, and Applications (OOPSLA 2009), Pages 81-96.

(included as doc/grace-oopsla09.pdf)