kandi X-RAY | ReLaXed Summary
kandi X-RAY | ReLaXed Summary
Top functions reviewed by kandi - BETA
- Waits for a page to wait for a page to arrive in out of the page
- Parses the given locals and returns a JSON string
- Parse a string to a JSON object
- Asynchronously reads a JSON file
- print error
- Determines whether the last json path is the last local file .
- Check if a path is a JSON file
ReLaXed Key Features
ReLaXed Examples and Code Snippets
r'(?:id|ID)=(?P\d+)' r'(id|ID)=(?P\d+)' some fancy title title = self._search_regex( r']+class="title"[^>]*>([^<]+)', webpage, 'title') title = self._search_regex( r']+class=(["\'])title\1[^>]*>(?P[^<]+)
def build_recursive_hd_all_reduce(input_tensors, red_op, un_op=None): """Construct a subgraph for recursive halving-doubling all-reduce. The recursive halving-doubling algorithm is described in (Thakur et al., 2015). The concept is to arran
def _unable_to_call_layer_due_to_serialization_issue( layer, *unused_args, **unused_kwargs): """Replaces the `layer.call` if the layer was not fully serialized. Keras Model/Layer serialization is relatively relaxed because SavedModels are
Trending Discussions on ReLaXed
I've been reading this post of Jeff Preshing about The Synchronizes-With Relation, and also the "Release-Acquire Ordering" section in the std::memory_order page from cpp reference, and I don't really understand:
It seems that there is some kind of promise by the standard that I don't understand why it's necessary. Let's take the example from the CPP reference:...
ANSWERAnswered 2022-Mar-29 at 15:00
ptr.store(p, std::memory_order_release) (L1) guarantees that anything done prior to this line in this particular thread (T1) will be visible to other threads as long as those other threads are reading
ptr in a correct fashion (in this case, using
std::memory_order_acquire). This guarantee works only with this pair, alone this line guarantees nothing.
Now you have
ptr.load(std::memory_order_acquire) (L2) on the other thread (T2) which, working with its pair from another thread, guarantees that as long as it read the value written in T1 you can see other values written prior to that line (in your case it is
data). So because L1 synchronizes with L2,
data = 42; happens before
assert(data == 42).
Also there is a guarantee that
ptr is written and read atomically, because, well, it is atomic. No other guarantees or promises are in that code.
I have a question about the definition of the synchronises-with relation in the C++ memory model when relaxed and acquire/release accesses are mixed on one and the same atomic variable. Consider the following example consisting of a global initialiser and three threads:...
ANSWERAnswered 2022-Mar-17 at 14:01
Because you use relaxed ordering on a separate load & store in T2, the release sequence is broken and the second assert can trigger (although not on a TSO platform such as X86).
You can fix this by either using acq/rel ordering in thread T2 (as you suggested) or by modifying T2 to use an atomic read-modify-write operation (RMW), like this:
I am working with post-processing of the log file arranged in the following format:...
ANSWERAnswered 2022-Mar-08 at 12:41
You may use this
in a lock-free queue.pop(), I read a trivialy_copyable variable (of integral type) after synchronization with an atomic aquire inside a loop. Minimized pseudo code:...
ANSWERAnswered 2022-Feb-20 at 23:05
Yes, it's UB in ISO C++;
value = data[oldReadPosition] in the C++ abstract machine involves reading the value of that object. (Usually that means lvalue to rvalue conversion, IIRC.)
But it's mostly harmless, probably only going to be a problem on machines with hardware race detection (not normal mainstream CPUs, but possibly on C implementations like clang with threadsanitizer).
Another use-case for non-atomic read and then checking for possible tearing is the SeqLock, where readers can prove no tearing by reading the same value from an atomic counter before and after the non-atomic read. It's UB in C++, even with
volatile for the non-atomic data, although that may be helpful in making sure the compiler-generated asm is safe. (With memory barriers and current handling of atomics by existing compilers, even non-volatile makes working asm). See Optimal way to pass a few variables between 2 threads pinning different CPUs
atomic_thread_fence is still necessary for a SeqLock to be safe, and some of the necessary ordering of atomic loads wrt. non-atomic may be an implementation detail if it can't sync with something and create a happens-before.
People do use Seq Locks in real life, depending on the fact that real-life compilers de-facto define a bit more behaviour than ISO C++. Or another way to put it is that happen to work for now; if you're careful about what code you put around the non-atomic read it's unlikely for a compiler to be able to do anything problematic.
But you're definitely venturing out past the safe area of guaranteed behaviour, and probably need to understand how C++ compiles to asm, and how asm works on the target platforms you care about; see also Who's afraid of a big bad optimizing compiler? on LWN; it's aimed at Linux kernel code, which is the main user of hand-rolled atomics and stuff like that.
I have a shared data structure that is already internally synchronised with a mutex. Can I use an atomic with memory order relaxed to signal changes. A very simplified view of what I mean in code
ANSWERAnswered 2022-Feb-10 at 16:08
Relaxed order means that ordering of atomics and external operations only happens with regard to operations on the specific atomic object (and even then, the compiler is free to re-order them outside of the program-defined order). Thus, a relaxed store has no relationship to any state in external objects. So a relaxed load will not synchronize with your other mutexes.
The whole point of acquire/release semantics is to allow an atomic to control visibility of other memory. If you want an atomic load to mean that something is available, it must be an acquire and the value it acquired must have been released.
What would be the minimally needed memory barriers in the following scenario?
Several threads update the elements of an array
int a[n] in parallel.
All elements are initially set to zero.
Each thread computes a new value for each element; then,
it compares the computed new value to the existing value stored in the array,
and writes the new value only if it is greater than the stored value.
For example, if a thread computes for
a a new value
a is already
10, then the thread should not update
But if the thread computes a new value
then the thread must update
The computation of the new values involves some shared read-only data; it does not involve the array at all.
While the above-mentioned threads are running, no other thread accesses the array. The array is consumed later, after all the threads are guaranteed to finish their updates.
The implementation uses a compare-and-swap loop, wrapping the elements
atomic_ref (either from Boost or from C++20):
ANSWERAnswered 2022-Feb-08 at 20:54
Relaxed is fine, you don't need any ordering wrt. access to any other elements during the process of updating. And for accesses to the same location, ISO C++ guarantees that a "modification order" exists for each location separately, and that even
relaxed operations will only see the same or later values in the modification order of the location between loaded or RMWed.
You're just building an atomic
fetch_max primitive out of a CAS retry loop. Since the other writers are doing the same thing, the value of each location is monotonically increasing. So it's totally safe to bail out any time you see a value greater than the
For the main thread to collect the results at the end, you do need release/acquire synchronization like
thread.join or some kind of flag. (e.g. maybe
fetch_sub(1, release) of a counter of how many threads still have work left to do, or an array of
done flags so you can just do a pure store.)
BTW, this seems likely to be slow, with lots of time spent waiting for cache lines to bounce between cores. (Lots of false-sharing.) Ideally you you can efficiently change this to have each thread work on different parts of the array (e.g. computing multiple candidates for the same index so it doesn't need any atomic stuff).
I cannot guarantee that the computed indices do not overlap. In practice, the overlapping is usually small, but it cannot be eliminated.
So apparently that's a no. And if the indices touched by different threads are in different cache lines (chunk of 16
int32_t) then there won't be too much false sharing. (Also, if computation is expensive so you aren't producing values very fast, that's good so atomic updates aren't what your code is spending most of its time on.)
But if there is significant contention and the array isn't huge, you could give each thread its own output array, and collect the results at the end. e.g. have one thread do
a[i] = max(a[i], b[i], c[i], d[i]) for 4 to 8 arrays per loop. (Not too many read streams at once, and not a variable number of inputs because that probably couldn't compile efficiently). This should benefit from SIMD, e.g. SSE4.1
pmaxsd doing 4 parallel
max operations, so this should be limited mostly by L3 cache bandwidth.
Or divide the max work between threads as a second parallel phase, with each thread doing the above over part of the output array. Or have the
thread_id % 4 == 0 reduce results from itself and the next 3 threads, so you have a tree of reductions if you have a system with many threads.
I basically have the following code snippet:...
ANSWERAnswered 2021-Sep-20 at 14:16
To answer the question in your title, there is no real relationship between atomics and sequence points.
The code as written does guarantee that the compiler must execute the
atomic_fetch_sub before the
atomic_load. But these functions are (in C's memory model) simply requests to the platform to perform certain actions on certain pieces of memory. Their effects, when they become visible to who, are specified by the memory model, and the ordering parameters. Thus even in the case when you know request A comes before request B, that does not mean the effects of request A are resolved before request B, unless you explicitly specify it to be.
Hey I am getting this kind of weird issue. I don't understand why this is causing in my unit test. Can someone please guide me what is missing in my side....
ANSWERAnswered 2022-Jan-26 at 15:04
When unit testing, you have to replace Dispatchers.Main with a different dispatcher than it has by default, because the default implementation of Dispatchers.Main doesn't exist when not running a full application. To do this, you need to have the
kotlinx-coroutines-test test dependency if you don't already:
I'm building my project with Vue.js 3, Vite.js. The app works fine when in dev mode (when using the dev server). Once I do launch the build command, Vite creates for me the /dist directory containing the build for my app. If I run the preview command (vite preview) it starts with no problem the preview of my build.
The problem is with some images which are coming from Vue components. All the images of my project are in the src/assets directory....
ANSWERAnswered 2022-Jan-24 at 11:27
Instead of using relative path
(..) to the assets folder, you can use
@/assets from any of the vue components to refer to files in the assets folder.
E.g this should work, no matter how deep the Vue component is nested.
I basically want to make a picture and div with whitespace-nowrap be in one horizontal line regardless of the screen size using tailwind css. First of all, here is a picture when I have it on full screen:
Just to be clear, I don't mind my text going over the screen due to whitespace-nowrap. However, I want my picture to be on the RIGHT side of the paragraph, not on the paragraph like below. So, I want my picture to be on the right side even though we won't be able to see the picture on the screen(unless ofcourse you scroll right). Here is my html:...
ANSWERAnswered 2022-Jan-23 at 09:07
First of all You have few
cssConflicts in first
I allowed myself to remove them, next You can see the rest below, I hope I understand You well and You will be satisfied ;-) And if You would like the
image on the right to look better, I suggest adjusting the
text on the left to the screen resolution ;-)
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