KDB: A Multi-threaded Debugger for Multi-threaded Applications

Introduction Concurrent programs contain both sequential and concurrent errors. While deadlock and race conditions are unique to concurrent programs, there also exist algorithmic design errors, such as inhibiting concurrency, which are unknown in the sequential domain. Recently, there has been a large effort in debugging race conditions [16], both statically [8] and dynamically [7], and to a lesser extent, deadlock [13]. Our experience shows that concurrent errors occur with diminishing frequency in the order: traditional sequential errors, algorithmic design errors, deadlock, race conditions. However, the difficulty in determining and fixing these errors grows exponentially from sequential errors to race conditions. Our experience also shows that the frequency of deadlock and race-conditions diminishes significantly when high-level concurrency constructs (e.g., task, monitor, actor, etc.) are used, versus thread and lock programming. We believe the best way to improve concur