ThreadScan

Abstract

The concurrent memory reclamation problem is that of devising a way for a deallocating thread to verify that no other concurrent threads hold references to a memory block being deallocated. To date, in the absence of automatic garbage collection, there is no satisfactory solution to this problem; existing tracking methods like hazard pointers, reference counters, or epoch-based techniques like RCU, are either prohibitively expensive or require significant programming expertise, to the extent that implementing them efficiently can be worthy of a publication. None of the existing techniques are automatic or even semi-automated.In this paper, we take a new approach to concurrent memory reclamation: instead of manually tracking access to memory locations as done in techniques like hazard pointers, or restricting shared accesses to specific epoch boundaries as in RCU, our algorithm, called ThreadScan, leverages operating system signaling to automatically detect which memory locations are being accessed by concurrent threads.Initial empirical evidence shows that ThreadScan scales surprisingly well and requires negligible programming effort beyond the standard use of Malloc and Free.

Decoupling lock-free data structures from memory reclamation for static analysis

“…ThreadScan (TS) [Alistarh et al 2015]. Modified version of hazard pointers which uses signaling to protect nodes on demand.…”

Pointer life cycle types for lock-free data structures with memory reclamation

“…Optimized HP implementations include the work by Aghazadeh et al [2014], the work by Dice et al [2016], and Cadence [Balmau et al 2016]. Dynamic Collect [Dragojevic et al 2011], StackTrack [Alistarh et al 2014], and ThreadScan [Alistarh et al 2015] are HP-esque implementations exploring the use of operating system and hardware support. Drop the Anchor [Braginsky et al 2013], Optimistic Access [Cohen and Petrank 2015b], Automatic Optimistic Access [Cohen and Petrank 2015a], QSense [Balmau et al 2016], Hazard Eras [Ramalhete and Correia 2017], and Interval-based Reclamation [Wen et al 2018] combine EBR and HP.…”

Every data structure deserves lock-free memory reclamation

“…However, the epoch-based reclamation scheme foils the lock-freedom guarantee of the data structure; and the reference-counting and hazard-pointers schemes add significant overhead [Hart et al 2007]. Recently, there has been a significant interest in designing lock-free reclamation schemes that support the lock-freedom progress guarantee, yet they do not add significant overhead [Alistarh et al 2017[Alistarh et al , 2015Balmau et al 2016;Braginsky et al 2013;Brown 2015;Cohen and Petrank 2015a,b;Dice et al 2016].…”

“…This data structure offers stronger progress guarantees (i.e., wait-free searches) and better performance than the Harris-Michael linked list [Cohen and Petrank 2015a]. Other recent memory-reclamation schemes [Alistarh et al 2015;Balmau et al 2016;Braginsky et al 2013;Brown 2015;Cohen and Petrank 2015b;Dice et al 2016] are similarly incompatible with the Harris and Harris-Herlihy-Shavit linked-list data structures.In this paper, we present Free Access: the first memory-reclamation scheme that stands up to the expectations of the data-structure designers. The Free Access scheme does not require the data structure to satisfy any algorithmic properties, hence making it generally applicable for existing and future lock-free data structures.…”

“…This data structure offers stronger progress guarantees (i.e., wait-free searches) and better performance than the Harris-Michael linked list [Cohen and Petrank 2015a]. Other recent memory-reclamation schemes [Alistarh et al 2015;Balmau et al 2016;Braginsky et al 2013;Brown 2015;Cohen and Petrank 2015b;Dice et al 2016] are similarly incompatible with the Harris and Harris-Herlihy-Shavit linked-list data structures.…”