A Relaxed Guide to memory_order_relaxed Hans Boehm Paul E. McKenney Google Facebook CPPCON 2020std::atomic/std::atomic_ref and memory_order_relaxed ● C++ atomic ● In particular, memory_order_relaxed allows arbitrary visibility reordering with respect to accesses to other locations.What is Not to Like About memory_order_relaxed? ● Just a load, just a store: ○ Assuming aligned machine-sized atomic objects, that is…What is Not to Like About memory_order_relaxed? ● Just a load, just a store: Full control, excellent efficiency and scalability! ○ Assuming aligned

(T1, T1, T2)") from a device function("func") is not allowed ... The experimental flag ’--expt-relaxed-constexpr’ can be used to allow this.33/66 Motivation Patterns The dark path Cuda proposal Thank and --expt-relaxed-constexpr34/66 Motivation Patterns The dark path Cuda proposal Thank you constexpr everything - 3 known uses RAPIDS1 by Nvidia: Discussed whether to use --expt-relaxed-constexpr, uses RAPIDS1 by Nvidia: Discussed whether to use --expt-relaxed-constexpr, but eventually decided against it MatX2 by Nvidia: Uses --expt-relaxed-constexpr 1Data science and AI library 2Matrix functions34/66

}; 27auto Fifo3::push(T const& value) { auto pushCursor = pushCursor_.load(std::memory_order_relaxed); auto popCursor = popCursor_.load(std::memory_order_acquire); if (full(pushCursor, popCursor)) pushCursor_.load(std::memory_order_acquire); auto popCursor = popCursor_.load(std::memory_order_relaxed); if (empty(pushCursor, popCursor)) { return false; } value = *element(popCursor); e value); };auto Fifo4::push(T const& value) { auto pushCursor = pushCursor_.load(std::memory_order_relaxed); if (full(pushCursor, cachedPopCursor_)) { cachedPopCursor_ = popCursor_.load(std::memory_order_acquire);

Drivers for Change ▶ Architectural demands to utilize multicore resources ▶ General acceptance of relaxed semantics ▶ The intractable O(n!) complexity of concurrent system models prompting the search for and Performance ▶ Previous works focus on relaxed correctness conditions ▶ Relaxed semantics is a technique, not a measurement ▶ Need to measure what relaxed semantics and other techniques do ▶ How correct Conclusion Key Take-Aways ▶ Quantifiability enables highly scalable data structures by permitting relaxed semantics ▶ The vector space model facilitates an efficient verification technique for checking

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 Relaxed Binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AnotherComponent bean in manner similar to the preceding AcmeProperties example. Relaxed Binding Spring Boot uses some relaxed rules for binding Environment properties to @ConfigurationProperties beans, firstName; } } With the preceding code, the following properties names can all be used: Table 5. relaxed binding Property Note acme.my- project.person.fir st-name Kebab case, which is recommended for

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 Relaxed Binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AnotherComponent bean in manner similar to the preceding AcmeProperties example. Relaxed Binding Spring Boot uses some relaxed rules for binding Environment properties to @ConfigurationProperties beans, firstName; } } With the preceding code, the following properties names can all be used: Table 5. relaxed binding Property Note acme.my- project.person.fir st-name Kebab case, which is recommended for

Multi-profile YAML documents YAML shortcomings Typesafe Configuration Properties Third-party configuration Relaxed binding @ConfigurationProperties Validation 24. Profiles Adding active profiles Programmatically Boot production ready starters 13.3. Spring Boot technical starters 22.1. Banner variables 23.1. relaxed binding 25.1. Logging properties Spring Boot Reference Guide Phillip Webb Dave Syer Josh Long FooComponent bean in a similar manner as the ConnectionSettings example above. Relaxed binding Spring Boot uses some relaxed rules for binding Environment properties to @ConfigurationProperties beans, so

Multi-profile YAML documents YAML shortcomings Typesafe Configuration Properties Third-party configuration Relaxed binding @ConfigurationProperties Validation 24. Profiles Adding active profiles Programmatically Boot production ready starters 13.3. Spring Boot technical starters 22.1. Banner variables 23.1. relaxed binding 25.1. Logging properties Spring Boot Reference Guide Phillip Webb Dave Syer Josh Long FooComponent bean in a similar manner as the ConnectionSettings example above. Relaxed binding Spring Boot uses some relaxed rules for binding Environment properties to @ConfigurationProperties beans, so

Multi-profile YAML documents YAML shortcomings Typesafe Configuration Properties Third-party configuration Relaxed binding @ConfigurationProperties Validation 24. Profiles Adding active profiles Programmatically Boot production ready starters 13.3. Spring Boot technical starters 22.1. Banner variables 23.1. relaxed binding 25.1. Logging properties Spring Boot Reference Guide Phillip Webb Dave Syer Josh Long FooComponent bean in a similar manner as the ConnectionSettings example above. Relaxed binding Spring Boot uses some relaxed rules for binding Environment properties to @ConfigurationProperties beans, so

Multi-profile YAML documents YAML shortcomings Typesafe Configuration Properties Third-party configuration Relaxed binding @ConfigurationProperties Validation 24. Profiles Adding active profiles Programmatically Boot production ready starters 13.3. Spring Boot technical starters 22.1. Banner variables 23.1. relaxed binding 25.1. Logging properties Spring Boot Reference Guide Phillip Webb Dave Syer Josh Long FooComponent bean in a similar manner as the ConnectionSettings example above. Relaxed binding Spring Boot uses some relaxed rules for binding Environment properties to @ConfigurationProperties beans, so