Modern transactional response-time sensitive applications have run into practical limits on the size of garbage collected heaps. The heap can only grow until GC pauses exceed the responsetime limits. Sustainable, scalable concurrent collection has become a feature worth paying for.Azul Systems has built a custom system (CPU, chip, board, and OS) specifically to run garbage collected virtual machines. The custom CPU includes a read barrier instruction. The read barrier enables a highly concurrent (no stop-the-world phases), parallel and compacting GC algorithm. The Pauseless algorithm is designed for uninterrupted application execution and consistent mutator throughput in every GC phase.Beyond the basic requirement of collecting faster than the allocation rate, the Pauseless collector is never in a "rush" to complete any GC phase. No phase places an undue burden on the mutators nor do phases race to complete before the mutators produce more work. Portions of the Pauseless algorithm also feature a "self-healing" behavior which limits mutator overhead and reduces mutator sensitivity to the current GC state.We present the Pauseless GC algorithm, the supporting hardware features that enable it, and data on the overhead, efficiency, and pause times when running a sustained workload.

C4, the Continuously Concurrent Compacting Collector, an updated generational form of the Pauseless GC Algorithm [7], is introduced and described, along with details of its implementation on modern X86 hardware. It uses a read barrier to support concurrent compaction, concurrent remapping, and concurrent incremental update tracing. C4 differentiates itself from other generational garbage collectors by supporting simultaneous-generational concurrency: the different generations are collected using concurrent (non stop-the-world) mechanisms that can be simultaneously and independently active. C4 is able to continuously perform concurrent young generation collections, even during long periods of concurrent full heap collection, allowing C4 to sustain high allocation rates and maintain the efficiency typical to generational collectors, without sacrificing response times or reverting to stop-the-world operation. Azul systems has been shipping a commercial implementation of the Pauseless GC mechanism, since 2005. Three successive generations of Azul's Vega series systems relied on custom multi-core processors and a custom OS kernel to deliver both the scale and features needed to support Pauseless GC. In 2010, Azul released its first software-only commercial implementation of C4 for modern commodity X86 hardware, using Linux kernel enhancements to support the required feature set. We discuss implementation details of C4 on X86, including the Linux virtual and physical memory management enhancements that were used to support the high rate of virtual memory operations required for sustained pauseless operation. We discuss updates to the collector's management of the heap for efficient generational collection and provide throughput and pause time data while running sustained workloads.

An interactive data fusion methodology of video, audio and nonlinear structural dynamic analysis for potential application in forensic engineering applications is piesented.The methodology was developed and successfully demonstrated in the analysis of a heavy transportable bridge collapse during preparation for testing. In this event multiple bridge elements failures were identified after the collapse including fractuie, cracks and npmre of high performance structural materials. A hand held camcorder provided the only recorded source of information about the collapse sequence in the form of a low quality and extremely unstable videotape recording.User assisted numerical algorithms were utilized to stabilize and enhance the digitized video sequence and to produce an filtered audio account of the collapse sequence. The interactive data fusion methodology was manifested by user assistance in the process of extracting, identifying, measuring and correlating relevant audio and video information from the videotaped recording with dynamic nonlinear structural analysis of postulated bridge failure sequences.The interactive data fusion methodology produced a conclusive account of the sequence of events during the bridge collapse. It clearly identified the failure mechanism and enabled the timely correction of the failure cause.476

We describe the Collie collector, a fully concurrent compacting collector that uses transactional memory techniques to achieve waitfree compaction. The collector uses compaction as the primary means of reclaiming unused memory, and performs "individual object transplantations" as transactions. We introduce new terms and requirements useful for analyzing concurrent relocating collectors, including definitions of referrer sets, object transplantation and the notion of individually transplantable objects. The Collie collector builds on these terms and on a detailed analysis of an object's legal states during compaction.Collie uses a combination of read barriers, write barriers and transactional memory operations. Its read-barrier supports fast, direct object referencing while using a bound, constant time, waitfree triggering path. Collie thereby avoids the constant indirection cost of Brooks [9] style barriers or handle-based heaps [25]. Collie is demonstrated using speculative multi-address atomicity [11], a form of hardware transactional memory supported by the Azul Vega architecture [2].We evaluate the Collie collector on the Azul platform, on which previous concurrent collectors such as the Pauseless Collector [12] and its generational variant [30] have been commercially available for several years. We discuss Collie's performance while running sustained workloads, and compare it to the Pauseless collector on the same platform. The Collie collector provides significant MMU [5] improvements even in the 1-msec time windows compared to the Pauseless collector. At the same time, it matches Pauseless in throughput and in the ability to scale to large heap sizes.We believe that the Collie collector is the first garbage collector to leverage hardware-assisted transactional memory. While Collie directly leverages Vega's speculative multi-address atomicity feature (SMA) [11], its design can be easily adapted to other hardwareassisted transactional memory systems. Specifically, the upcoming Intel TSX instruction set extensions [21] include capabilities similar to SMA. We expect Collie to be easily implementable on future Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee.

C4, the Continuously Concurrent Compacting Collector, an updated generational form of the Pauseless GC Algorithm [7], is introduced and described, along with details of its implementation on modern X86 hardware. It uses a read barrier to support concurrent compaction, concurrent remapping, and concurrent incremental update tracing. C4 differentiates itself from other generational garbage collectors by supporting simultaneous-generational concurrency: the different generations are collected using concurrent (non stop-the-world) mechanisms that can be simultaneously and independently active. C4 is able to continuously perform concurrent young generation collections, even during long periods of concurrent full heap collection, allowing C4 to sustain high allocation rates and maintain the efficiency typical to generational collectors, without sacrificing response times or reverting to stop-the-world operation. Azul systems has been shipping a commercial implementation of the Pauseless GC mechanism, since 2005. Three successive generations of Azul's Vega series systems relied on custom multi-core processors and a custom OS kernel to deliver both the scale and features needed to support Pauseless GC. In 2010, Azul released its first software-only commercial implementation of C4 for modern commodity X86 hardware, using Linux kernel enhancements to support the required feature set. We discuss implementation details of C4 on X86, including the Linux virtual and physical memory management enhancements that were used to support the high rate of virtual memory operations required for sustained pauseless operation. We discuss updates to the collector's management of the heap for efficient generational collection and provide throughput and pause time data while running sustained workloads.