isabella232 / concurrent-ll

concurrent linked list implementation

Overview

This package contains the skeleton code for implementing and evaluating two concurrent linked lists: a lock-free and a lock-based. The implementations should work on any Linux-based x86 environments.

Both lists are sorted and provide three main operations:

• adding an element to the list (if not already in the list)
• removing an element from the list (if already in the list)
• looking for an element in the list

In our case, a node of the list contains at least an integer key.

The lock-based implementation will use a technique called "hand-over-hand locking", while the lock-free will be based on Harris' algorithm (reference below).

Reference

Lock-free linkedlist implementation of Harris' algorithm

"A Pragmatic Implementation of Non-Blocking Linked Lists" T. Harris, p. 300-314, DISC 2001.

Build

You can compile the code (in Linux) by calling:

make

in the base directory.

If the number of cores on your processor is not recognized properly, fix it in include/utils.h. file under the "#if defined(DEFAULT)" definitions.

You can verify by calling:

make check

Benchmarking

You can invoke the benchmarking scripts by calling:

make bench

Tools

You can find several useful scripts that will help you test and evaluate your implementations.

In details:

• scripts/test_correctness.sh: test the correctness of an implementation, by stressing it
• scripts/scalability1.sh: benchmark 1 application and get its throughput and scalability E.g., scripts/scalability1.sh all ./out/test-lock -i128
• scripts/scalability2.sh: benchmark 2 applications and get their throughput and scalability E.g., scripts/scalability2.sh all ./out/test-lock ./out/test-lockfree -i100
• scripts/run_ll.sh: execute the workloads that will be part of the deliverable
• scripts/create_plots_ll.sh: generate the plots (int plots folder) of the data generated with scripts/run_ll.sh Note: You need gnuplot installed

Implementation

You can find an easy-to-use interface for atomic operations in include/atomic_ops.h.

• list.h: contains the interface and the structures of the list. You only need to change the llist_t and node_t structures to reflect the list and a node of a list of your implementations respectively.

• list.c: contains the implementations of the operations of the list, i.e., creating a new list and a new bucket, freeing the list, and, of course, adding, removing, and looking for an element in the list.

Additionally, for the lock-based version, you need to implement and use some locks. You can find the skeletons for initializing, freeing, locking, and unlocking a lock in include/lock_if.h.

Memory management is one of most cumbersome problems on lock-free data structures. In other words, when a thread removes an element (a node) from the structure, it cannot always free the memory for that node, because other threads might be holding a reference to this memory.

When using locks, memory management is rather straightforward, because of the mutual exclusion property of locks. You can optionally implement memory management on the lock-based version.