摘要:
A transactional memory implementation has been developed that is capable of coordinating concurrent hardware transactional memory (HTM) and software transactional memory (STM) transactions over a unified transactional memory space. Some implementations employ hardware transactional memory, if available or suitable, to improve performance. Some exploitations include a hardware transactional memory in which, or for which, hardware-mediated transactions are augmented to include within their transactional scope (or mechanism) one or more additional transactional locations that facilitate coordination with concurrently executing software-mediated transactions (if any).
摘要:
Transactional programming promises to substantially simplify the development and maintenance of correct, scalable, and efficient concurrent programs. Designs for supporting transactional programming using transactional memory implemented in hardware, software, and a mixture of the two have emerged recently. However, various features and capabilities for debugging programs executed using transactional memory are absent from conventional debuggers. Because transactional memory implementations provide the “illusion” of multiple memory locations changing value atomically, there are challenges involved with integrating debuggers with such programs to provide the user with a coherent view of program execution. For instance, when execution is halted for debugging, a user may request to view a transactional variable or memory location. The transactional variable or memory location may have a pre-transaction value and a tentative value. Allowing a user to only view one of the values reduces the capacity of a user to reason about the behavior of the code.
摘要:
Solutions to a value recycling problem that we define herein facilitate implementations of computer programs that may execute as multithreaded computations in multiprocessor computers, as well as implementations of related shared data structures. Some exploitations of the techniques described herein allow non-blocking, shared data structures to be implemented using standard dynamic allocation mechanisms (such as malloc and free). Indeed, we present several exemplary realizations of dynamic-sized, non-blocking shared data structures that are not prevented from future memory reclamation by thread failures and which depend (in some implementations) only on widely-available hardware support for synchronization. Some exploitations of the techniques described herein allow non-blocking, indeed even lock-free or wait-free, implementations of dynamic storage allocation for shared data structures. A class of general solutions to value recycling is described in the context of an illustration we call the Repeat Offender Problem (ROP), including illustrative Application Program Interfaces (APIs) defined in terms of the ROP terminology. Furthermore, specific solutions, implementations and algorithm, including a Pass-The-Buck (PTB) implementation are described.
摘要:
The design of nonblocking linked data structures using single-location synchronization primitives such as compare-and-swap (CAS) is a complex affair that often requires severe restrictions on the way pointers are used. One way to address this problem is to provide stronger synchronization operations, for example, ones that atomically modify one memory location while simultaneously verifying the contents of others. We provide a simple and highly efficient nonblocking implementation of such an operation: an atomic k-word-compare single-swap operation (KCSS). Our implementation is obstruction-free. As a result, it is highly efficient in the uncontended case and relies on contention management mechanisms in the contended cases. It allows linked data structure manipulation without the complexity and restrictions of other solutions. Additionally, as a building block of some implementations of our techniques, we have developed the first nonblocking software implementation of load-linked/store-conditional that does not severely restrict word size.
摘要:
We teach a powerful approach that greatly simplifies the design of non-blocking mechanisms and data structures, in part by, largely separate the issues of correctness and progress. At a high level, our methodology includes designing an “obstruction-free” implementation of the desired mechanism or data structure, which may then be combined with a contention management mechanism whose role is to facilitate the conditions under which progress of the obstruction-free implementation is assured. In general, the contention management mechanism is separable semantically from an obstruction-free concurrent shared/sharable object implementation to which it is/may be applied. In some cases, the contention management mechanism may actually be coded separately from the obstruction-free implementation. We elaborate herein on the notions of obstruction-freedom and contention management, and various possibilities for combining the two. In addition, we include description of some exemplary applications to particular concurrent software mechanisms and data structure implementations.
摘要:
One embodiment of the present invention provides a system that facilitates precise exception semantics for a virtual machine. During operation, the system executes a program in the virtual machine using a processor that includes a gated store buffer that stores values to be written to a memory. This gated store buffer is configured to delay a store to the memory until after a speculatively-optimized region of the program commits. The processor signals an exception when it detects that a load following the store is attempting to access the same memory region being written by the store prior to the commitment of the speculatively-optimized region.
摘要:
Systems and methods for implementing and using nonblocking zero-indirection software transactional memory (NZSTM) are disclosed. NZSTM systems implement object-based software transactional memory that eliminates all levels of indirection except in the uncommon case of a conflict with an unresponsive thread. Shared data is co-located with a header in an NZObject, and is addressable at a fixed offset from the header. Conflicting transactions are requested to abort themselves without being forced to abort. NZObjects are modified in place when there are no conflicts, and when a conflicting transaction acknowledges the abort request. In the uncommon case, NZObjects are inflated to introduce a locator and some levels of indirection, and are restored to their un-inflated form following resolution of the conflict. In some embodiments, transactions are executed using best effort hardware transactional memory if it is available and effective, and software transactional memory if not, yielding a hybrid transactional memory system, NZTM.
摘要:
In a multi-threaded computer system that uses transactional memory, object fields accessed by only one thread are accessed by regular non-transactional read and write operations. When an object may be visible to more than one thread, access by non-transactional code is prevented and all accesses to the fields of that object are performed using transactional code. In one embodiment, the current visibility of an object is stored in the object itself. This stored visibility can be checked at runtime by code that accesses the object fields or code can be generated to check the visibility prior to access during compilation.
摘要:
We propose a new form of software transactional memory (STM) designed to support dynamic-sized data structures, and we describe a novel non-blocking implementation. The non-blocking property we consider is obstruction-freedom. Obstruction-freedom is weaker than lock-freedom; as a result, it admits substantially simpler and more efficient implementations. An interesting feature of our obstruction-free STM implementation is its ability to use of modular contention managers to ensure progress in practice.
摘要:
Transactional programming promises to substantially simplify the development and maintenance of correct, scalable, and efficient concurrent programs. Designs for supporting transactional programming using transactional memory implemented in hardware, software, and a mixture of the two have emerged recently. Unfortunately, conventional debugging programs are often inadequate when employed in relation to code that employs transactional memory and new or modified techniques are needed. We describe techniques whereby certain facilities of a transactional memory implementation can be leveraged to provide replay debugging. With replay debugging, the user can examine a partial or complete execution of an atomic block after it has happened—for example, right before the execution commits. Moreover, in some cases the user can modify the replayed execution, and decide to commit the new modified execution instead of the original replayed one.