atomics | Lockless , wait-free and allocation-free tools for Java | Map library
kandi X-RAY | atomics Summary
kandi X-RAY | atomics Summary
Lockless, wait-free and allocation-free tools for Java. These tools are designed for situations where waiting to acquire a monitor or having garbage collections is not acceptable.
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Top functions reviewed by kandi - BETA
- Reads data from the buffer
- Encodes the given read claim
- Gets the claimed state
- Gets read state
- Calculates the number of bytes written by a given state
- Removes an item from the bag
- Returns a value in the given state
- Makes the removal of a given state
- Returns the size of the bag
- Retrieves an item from the bag
- Returns the next free mask
- Acquires an item from the queue
- Returns the next item
- Reads the contents of this mirror into the given image
- Updates the image stored in this mirror
- Blocks until a wait is complete
atomics Key Features
atomics Examples and Code Snippets
Community Discussions
Trending Discussions on atomics
QUESTION
In C++20, we got the capability to sleep on atomic variables, waiting for their value to change.
We do so by using the std::atomic::wait method.
Unfortunately, while wait has been standardized, wait_for and wait_until are not. Meaning that we cannot sleep on an atomic variable with a timeout.
Sleeping on an atomic variable is anyway implemented behind the scenes with WaitOnAddress on Windows and the futex system call on Linux.
Working around the above problem (no way to sleep on an atomic variable with a timeout), I could pass the memory address of an std::atomic to WaitOnAddress on Windows and it will (kinda) work with no UB, as the function gets void* as a parameter, and it's valid to cast std::atomic to void*
On Linux, it is unclear whether it's ok to mix std::atomic with futex. futex gets either a uint32_t* or a int32_t* (depending which manual you read), and casting std::atomic to u/int* is UB. On the other hand, the manual says
The uaddr argument points to the futex word. On all platforms, futexes are four-byte integers that must be aligned on a four- byte boundary. The operation to perform on the futex is specified in the futex_op argument; val is a value whose meaning and purpose depends on futex_op.
Hinting that alignas(4) std::atomic should work, and it doesn't matter which integer type is it is as long as the type has the size of 4 bytes and the alignment of 4.
Also, I have seen many places where this trick of combining atomics and futexes is implemented, including boost and TBB.
So what is the best way to sleep on an atomic variable with a timeout in a non UB way? Do we have to implement our own atomic class with OS primitives to achieve it correctly?
(Solutions like mixing atomics and condition variables exist, but sub-optimal)
...ANSWER
Answered 2021-Jun-15 at 20:48You shouldn't necessarily have to implement a full custom atomic API, it should actually be safe to simply pull out a pointer to the underlying data from the atomic and pass it to the system.
Since std::atomic does not offer some equivalent of native_handle like other synchronization primitives offer, you're going to be stuck doing some implementation-specific hacks to try to get it to interface with the native API.
For the most part, it's reasonably safe to assume that first member of these types in implementations will be the same as the T type -- at least for integral values [1]. This is an assurance that will make it possible to extract out this value.
... and casting
std::atomictou/int*is UB
This isn't actually the case.
std::atomic is guaranteed by the standard to be Standard-Layout Type. One helpful but often esoteric properties of standard layout types is that it is safe to reinterpret_cast a T to a value or reference of the first sub-object (e.g. the first member of the std::atomic).
As long as we can guarantee that the std::atomic contains only the u/int as a member (or at least, as its first member), then it's completely safe to extract out the type in this manner:
QUESTION
I have set a react-native project with the cli. It works, but I have a very anoying eslint error:
Strings must use singlequote.eslint(quotes)
I have tried to write this:
...ANSWER
Answered 2021-Jun-15 at 13:57You can turn off any specific rule like so:
QUESTION
In one of his great video, Jon Gjengset implements a mutex to notably understand the effect of std::sync::atomic::Ordering. The code is very simple : create a mutex that holds an integer and start many threads to add 1 to the integer concurrently and see the results. The code is here (I reproduce stricly Jon example) : https://github.com/fmassot/atomics-rust
When using correct ordering, we expect the program to make additions atomically and check the result as the sum of all added values. The code does several times on each thread the following actions :
- call compare_exchange_weak with Ordering::Acquire to get the lock
- on success increment the value by one
- release the lock with Ordering::Release
Unfortunately it does not seem to work on linux/x86_64 nor on macbook/arm64.
The results when running cargo r --release are sometimes correct, sometimes wrong like this:
ANSWER
Answered 2021-Jun-06 at 22:47Problem solved, solution given by @user4815162342
The same value was used for LOCKED and UNLOCKED so there was no lock at all.
Conclusion, the error was stupid and coming from me...
QUESTION
So in rust, I want to have an atomically referenced count pointer, but I want that pointer to also be atomic. Meaning that for whatever pointer the Arc holds, it will free the memory pointed to by the pointer when the reference count is zero.
Say I have the following code in C++
...ANSWER
Answered 2021-May-20 at 05:33If you don't need to do manual deallocation or cleanup (are you using unsafe for allocation?), you don't need to to anything special. When the last Arc is dropped, it will call drop on the AtomicPtr. If you do need do to manual deallocation/cleanup, I think you could solve this by using making a struct PtrGuard(pub AtomicPtr>) that implements Drop (running your custom cleanup code), and your smart pointer type will be Arc>.
QUESTION
Let me start with the fact that I like asynchronous code. I would never wrap async code in a sync wrapper in production, but it is still something that I want to learn how to do. I am talking about specifically in Node.JS, not the browser. There are many ways to access the result of an async function synchronously like using child_process.spawnSync or a worker and Atomics. The issue with these ways is this:
ANSWER
Answered 2021-May-18 at 22:01I found the npm package deasync. In it, there is a line of code: process._tickCallback(). I implemented it as a function. This will only resolve a promise that has been completely fulfilled. For example:
QUESTION
There is an interesting article about ARM8.1 Graviton 2 offering of AWS. This article has tests for CPU coherency where I am trying to repeat.
There is C++ code repo in GitHub named core-latency using Nonius Micro-benchmarking.
I managed to replicate the first test without atomic instructions using the command below to compile:
...ANSWER
Answered 2021-Apr-30 at 09:51After doing some more experiments, I found the problem. In the code snippet below are the steps:
- making a comparison first (if state equals Ping)
- calling the class method
setto do an atomic store operation.
Code snippet from core-latency:
QUESTION
This is my implementation of a lockless, waitless, multithread-safe MPMC queue using only atomics:
...ANSWER
Answered 2021-Apr-26 at 06:08If the other bugs are fixed, most likely start, end, and precount can all be memory_order_relaxed in all uses.
postcount is the variable that signifies that a value has been written to the queue. ie it controls the publishing of the value, and the reading of the value.
So postcount needs memory_order_release ("publish") in push, and memory_order_acquire before reading (ie in pop).
Maybe.
QUESTION
The implementation of emulated atomics in openCL following the STREAM blog works nicely for atomic add in 32bit, on CPU as well as NVIDIA and AMD GPUs.
The 64bit equivalent based on the cl_khr_int64_base_atomics extension seems to run properly on (pocl and intel) CPU as well as NVIDIA openCL drivers.
I fail to make 64bit work on AMD GPU cards though -- both on amdgpu-pro and rocm (3.5.0) environments, running on a Radeon VII and a Radeon Instinct MI50, respectively.
The implementation goes as follows:
...ANSWER
Answered 2021-Apr-22 at 11:41For 64-bit, the function is called atom_cmpxchg and not atomic_cmpxchg.
QUESTION
Receiving this error when attempting to install pg_query -v '1.0.2 gem on ruby 2.6.6 on an M1 Mac.
Here's the full trace:
...ANSWER
Answered 2021-Apr-21 at 12:40For posterity, I had to upgrade to pg_query 1.3.0 in order to get ARM support. https://github.com/pganalyze/pg_query/issues/210
QUESTION
This program will sometimes print 00, but if I comment out a.store and b.store and uncomment a.fetch_add and b.fetch_add which does the exact same thing i.e both set the value of a=1,b=1 , I never get 00. (Tested on an x86-64 Intel i3, with g++ -O2)
Am i missing something, or can "00" never occur by the standard?
This is the version with plain stores, which can print 00.
...ANSWER
Answered 2021-Apr-05 at 14:05I get "10" in both cases. The first thread will always run faster and a == 1! But if you add additional operations to foo()
Community Discussions, Code Snippets contain sources that include Stack Exchange Network
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Install atomics
You can use atomics like any standard Java library. Please include the the jar files in your classpath. You can also use any IDE and you can run and debug the atomics component as you would do with any other Java program. Best practice is to use a build tool that supports dependency management such as Maven or Gradle. For Maven installation, please refer maven.apache.org. For Gradle installation, please refer gradle.org .
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