# Julia at Scale

**URL:** https://discourse.julialang.org/c/domain/parallel/34.md?page=13

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**Page:** 14

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## [Logical processes remain active after my parallelized program ends](https://discourse.julialang.org/t/logical-processes-remain-active-after-my-parallelized-program-ends/16338)

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**Author:** [@dsHitman](https://discourse.julialang.org/u/dsHitman)\
**Replies:** 4\
**Last updated:** [October 16, 2018, 10:06am UTC](https://discourse.julialang.org/t/logical-processes-remain-active-after-my-parallelized-program-ends/16338 "2018-10-16T10:06:45Z")

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Hi, I have developed a parallel version of a cellular automata but when the programm ends the logical process continue to remain active as the programm didn’t ends. Why?

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## [The sum of an array is faster in the sequential version than in the parallelized version](https://discourse.julialang.org/t/the-sum-of-an-array-is-faster-in-the-sequential-version-than-in-the-parallelized-version/16171)

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**Author:** [@dsHitman](https://discourse.julialang.org/u/dsHitman)\
**Replies:** 9\
**Last updated:** [October 11, 2018, 3:57pm UTC](https://discourse.julialang.org/t/the-sum-of-an-array-is-faster-in-the-sequential-version-than-in-the-parallelized-version/16171 "2018-10-11T15:57:19Z")

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I have an i7 with 8 logical process but the sum of an array is faster in the sequential versione than in the parallel. Why? Am I doing something wrong? Thanks for the answers. using Distributed x = rand(1000000) #print…

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## [Parallel without communication using MPI](https://discourse.julialang.org/t/parallel-without-communication-using-mpi/16016)

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**Author:** [@milankl](https://discourse.julialang.org/u/milankl)\
**Replies:** 3\
**Last updated:** [October 8, 2018, 5:54pm UTC](https://discourse.julialang.org/t/parallel-without-communication-using-mpi/16016 "2018-10-08T17:54:41Z")

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using MPI function main() MPI.Init() comm = MPI.COMM\_WORLD id = MPI.Comm\_rank(comm) # compile and initialize inv(rand(100,100)); A = rand(3500,3500) @time inv(A); println("$id of $(MPI.…

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## [My parallel cellular automata with Distributed Arrays is very slowly](https://discourse.julialang.org/t/my-parallel-cellular-automata-with-distributed-arrays-is-very-slowly/15998)

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**Author:** [@dsHitman](https://discourse.julialang.org/u/dsHitman)\
**Replies:** 0\
**Last updated:** [October 7, 2018, 6:31pm UTC](https://discourse.julialang.org/t/my-parallel-cellular-automata-with-distributed-arrays-is-very-slowly/15998 "2018-10-07T18:31:36Z")

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Hi, I tried to implement a Game Of Life in Julia using the distributed Array and the Distributed library to improve it and make it faster than the sequential version, but althoug I have a quad core i7 CPU the programm is…

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## [How can I speed up a batch of numerical integrations from a shared array?](https://discourse.julialang.org/t/how-can-i-speed-up-a-batch-of-numerical-integrations-from-a-shared-array/15925)

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**Author:** [@joshdorrington](https://discourse.julialang.org/u/joshdorrington)\
**Replies:** 1\
**Last updated:** [October 5, 2018, 1:40pm UTC](https://discourse.julialang.org/t/how-can-i-speed-up-a-batch-of-numerical-integrations-from-a-shared-array/15925 "2018-10-05T13:40:55Z")

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I am trying to carry out numerical integrations on a large number of initial conditions, storing them in a shared array: D=6 N=1000 T=150 state=SharedArray{Float64}((D,N,T)) state\[:,:,1\]=randn(D,N); @everywhere include…

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## [Memory Allocation of Channel Buffers of type Array](https://discourse.julialang.org/t/memory-allocation-of-channel-buffers-of-type-array/15655)

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**Author:** [@rohanmclure](https://discourse.julialang.org/u/rohanmclure)\
**Replies:** 0\
**Last updated:** [September 29, 2018, 7:55am UTC](https://discourse.julialang.org/t/memory-allocation-of-channel-buffers-of-type-array/15655 "2018-09-29T07:55:27Z")

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I have distributed workers wishing to perform an in-place distributed transpose. In this particular example, each worker has access to a ‘column block’ of a dense matrix, and workers must send off-diagonal sections of th…

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## [How does the future of ParallelAccelerator look like?](https://discourse.julialang.org/t/how-does-the-future-of-parallelaccelerator-look-like/15510)

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**Author:** [@MiguelGoncalves](https://discourse.julialang.org/u/MiguelGoncalves)\
**Replies:** 3\
**Last updated:** [September 27, 2018, 9:36am UTC](https://discourse.julialang.org/t/how-does-the-future-of-parallelaccelerator-look-like/15510 "2018-09-27T09:36:25Z")

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It seems I cannot add ParallelAccelerator to Julia 1.0 because it requires version 0.6. That being said, the last commit to the package is from October 2017. Are there any plans for: making the package compatible with …

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## [Why does RemoteChannel have few constructors.](https://discourse.julialang.org/t/why-does-remotechannel-have-few-constructors/15502)

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**Author:** [@YonghyunRyu](https://discourse.julialang.org/u/YonghyunRyu)\
**Replies:** 1\
**Last updated:** [September 26, 2018, 9:30am UTC](https://discourse.julialang.org/t/why-does-remotechannel-have-few-constructors/15502 "2018-09-26T09:30:49Z")

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The constructor that creates a RemoteChannel with a specific size and type requires a function as the first argument like RemoteChannel(()-\>Channel{Int}(10), pid). Using lambda functions as parameters is inconvenient be…

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## [Can't add Windows workers due to a missing sh shell](https://discourse.julialang.org/t/cant-add-windows-workers-due-to-a-missing-sh-shell/15055)

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**Author:** [@turtle](https://discourse.julialang.org/u/turtle)\
**Replies:** 4\
**Last updated:** [September 18, 2018, 12:40pm UTC](https://discourse.julialang.org/t/cant-add-windows-workers-due-to-a-missing-sh-shell/15055 "2018-09-18T12:40:07Z")

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I am trying to add workers on a Windows 10 node from a Windows 10 master. Identical Julia 0.7.0 and passwordless login are set up correctly. However addprocs( \[(remote\_ip,6)\] ) fails with the error message: ‘sh’ is no…

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## [Releasing processes by restarting the kernel](https://discourse.julialang.org/t/releasing-processes-by-restarting-the-kernel/15066)

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**Author:** [@Snir\_Gazit](https://discourse.julialang.org/u/Snir_Gazit)\
**Replies:** 0\
**Last updated:** [September 17, 2018, 1:08pm UTC](https://discourse.julialang.org/t/releasing-processes-by-restarting-the-kernel/15066 "2018-09-17T13:08:26Z")

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Does restarting a kernel (either from the command line or Jupyter) will also release running processes added by addprocs()? By looking at the CPU usage using top from the command line, it appears that this is not the cas…

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## [Some feedback while waiting for pmap](https://discourse.julialang.org/t/some-feedback-while-waiting-for-pmap/14970)

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**Author:** [@turtle](https://discourse.julialang.org/u/turtle)\
**Replies:** 9\
**Last updated:** [September 16, 2018, 10:24am UTC](https://discourse.julialang.org/t/some-feedback-while-waiting-for-pmap/14970 "2018-09-16T10:24:03Z")

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I am running a long calculation distributed on several workers and several computers: output = pmap( i-\>iter(i,parameters), 1:1000 ) While waiting I would like to know which i is being processed. How can I get this s…

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## [Calling Julia from HPC code](https://discourse.julialang.org/t/calling-julia-from-hpc-code/14680)

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**Author:** [@nurban](https://discourse.julialang.org/u/nurban)\
**Replies:** 3\
**Last updated:** [September 11, 2018, 7:05pm UTC](https://discourse.julialang.org/t/calling-julia-from-hpc-code/14680 "2018-09-11T19:05:22Z")

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I’m interested in the possibility of writing Julia functions as subroutines that can be invoked from a modern HPC code (i.e. something written in Fortran or C++, often with a compiler tuned to a specific supercomputer ar…

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## [Use Dynamic Arrays (Vectors) during Multi-threading](https://discourse.julialang.org/t/use-dynamic-arrays-vectors-during-multi-threading/14759)

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**Author:** [@SohamTamb](https://discourse.julialang.org/u/SohamTamb)\
**Replies:** 7\
**Last updated:** [September 10, 2018, 11:50pm UTC](https://discourse.julialang.org/t/use-dynamic-arrays-vectors-during-multi-threading/14759 "2018-09-10T23:50:16Z")

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Consider a situation where each thread is performing push! on a unique vector. i.e. no 2 threads can edit the same vector. This can cause a race condition because push! can invoke memory reallocation. If 2 different t…

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## [Windows 10 + Linux working together](https://discourse.julialang.org/t/windows-10-linux-working-together/14727)

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**Author:** [@turtle](https://discourse.julialang.org/u/turtle)\
**Replies:** 3\
**Last updated:** [September 9, 2018, 7:46pm UTC](https://discourse.julialang.org/t/windows-10-linux-working-together/14727 "2018-09-09T19:46:54Z")

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I have two computers, one running Windows 10 and the other running Ubuntu 14.04, both with the same version of the language: Julia 0.7.0. I would like to combine the computing power of the two computers, and control a…

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## [Help with data movement and commuication](https://discourse.julialang.org/t/help-with-data-movement-and-commuication/14672)

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**Author:** [@bbrunaud](https://discourse.julialang.org/u/bbrunaud)\
**Replies:** 1\
**Last updated:** [September 8, 2018, 5:37am UTC](https://discourse.julialang.org/t/help-with-data-movement-and-commuication/14672 "2018-09-08T05:37:09Z")

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Hello, I’ve been struggling for a long time with an apparently simple problem. Given a graph data structure with nodes inside I want to apply a function to each node that shares information across nodes and modifies the…

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## [Error when using @distributed for on cluster with multiple nodes](https://discourse.julialang.org/t/error-when-using-distributed-for-on-cluster-with-multiple-nodes/14377)

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**Author:** [@thehalfspace](https://discourse.julialang.org/u/thehalfspace)\
**Replies:** 4\
**Last updated:** [August 31, 2018, 9:02pm UTC](https://discourse.julialang.org/t/error-when-using-distributed-for-on-cluster-with-multiple-nodes/14377 "2018-08-31T21:02:24Z")

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I have a code with some simple @sync @distributed for loops. It works fine when I run it on my computer with 4 processors, or on the cluster with 1 node and any number of processors per node. But when I run it with more…

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## [Custom Modules with Distributed](https://discourse.julialang.org/t/custom-modules-with-distributed/14321)

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**Author:** [@gideonsimpson](https://discourse.julialang.org/u/gideonsimpson)\
**Replies:** 1\
**Last updated:** [August 30, 2018, 2:48pm UTC](https://discourse.julialang.org/t/custom-modules-with-distributed/14321 "2018-08-30T14:48:14Z")

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In 0.6.x of Julia, the following worked for me: modulepath = "/home/me/code/my\_modules"; addprocs(4); push!(LOAD\_PATH,modulepath); @everywhere using MyModule # rest of my code In the above, MyModule is some custom modu…

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## [Julia 1.0 Example of @distributed and pmap](https://discourse.julialang.org/t/julia-1-0-example-of-distributed-and-pmap/14064)

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**Author:** [@iwelch](https://discourse.julialang.org/u/iwelch)\
**Replies:** 1\
**Last updated:** [August 26, 2018, 2:56am UTC](https://discourse.julialang.org/t/julia-1-0-example-of-distributed-and-pmap/14064 "2018-08-26T02:56:14Z")

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I am unable to get @distributed (aka @parallel) to work, even with a trivial example. I get errors. is it obvious what I am doing wrong? $ julia \_ \_ \_ \_(\_)\_ | Documentation: https://docs.…

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## [Share a modules between processes](https://discourse.julialang.org/t/share-a-modules-between-processes/13903)

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**Author:** [@vitreo12](https://discourse.julialang.org/u/vitreo12)\
**Replies:** 0\
**Last updated:** [August 22, 2018, 7:51pm UTC](https://discourse.julialang.org/t/share-a-modules-between-processes/13903 "2018-08-22T19:51:46Z")

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Duplicate of: Share a module between two Worker processes Sorry for the mistake.

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## [Distributed for loop slower than serial?](https://discourse.julialang.org/t/distributed-for-loop-slower-than-serial/13722)

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**Author:** [@Panadestein](https://discourse.julialang.org/u/Panadestein)\
**Replies:** 4\
**Last updated:** [August 20, 2018, 7:28am UTC](https://discourse.julialang.org/t/distributed-for-loop-slower-than-serial/13722 "2018-08-20T07:28:07Z")

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Hello everyone. As the title of this post says, I have been trying to parallelize a for loop that is included in one of the programs I’m developing for my PhD thesis. This code was originally written in Python, but at so…

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## [Go-like select statement](https://discourse.julialang.org/t/go-like-select-statement/13684)

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**Author:** [@maurocchi](https://discourse.julialang.org/u/maurocchi)\
**Replies:** 0\
**Last updated:** [August 18, 2018, 9:35pm UTC](https://discourse.julialang.org/t/go-like-select-statement/13684 "2018-08-18T21:35:09Z")

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Is there in the Julia standard library something to mime the behaviour of the Golang select statement against the provided Channels?

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## [Share an already defined variable to all processes](https://discourse.julialang.org/t/share-an-already-defined-variable-to-all-processes/13421)

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**Author:** [@e3c6](https://discourse.julialang.org/u/e3c6)\
**Replies:** 3\
**Last updated:** [August 14, 2018, 5:20pm UTC](https://discourse.julialang.org/t/share-an-already-defined-variable-to-all-processes/13421 "2018-08-14T17:20:55Z")

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If I have a variable already defined in one process, how can I share it with all the other processes? @everywhere foo=1 does this for a new definition of foo. But suppose I already assigned foo to a value in the current…

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## [Memory allocation in multi-thread vs single-thread](https://discourse.julialang.org/t/memory-allocation-in-multi-thread-vs-single-thread/12999)

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**Author:** [@aabrkay](https://discourse.julialang.org/u/aabrkay)\
**Replies:** 0\
**Last updated:** [August 7, 2018, 3:23pm UTC](https://discourse.julialang.org/t/memory-allocation-in-multi-thread-vs-single-thread/12999 "2018-08-07T15:23:38Z")

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Dear All, I have a question about the significant difference in memory allocation between the multi-threads and single threads. I was experimenting Walk on Sphere method for Poisson equation, which is an embarrassingly p…

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## [Distributed computing of x = A \\ b](https://discourse.julialang.org/t/distributed-computing-of-x-a-b/12716)

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**Author:** [@ahojukka5](https://discourse.julialang.org/u/ahojukka5)\
**Replies:** 6\
**Last updated:** [July 29, 2018, 8:40pm UTC](https://discourse.julialang.org/t/distributed-computing-of-x-a-b/12716 "2018-07-29T20:40:27Z")

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N = 1000 x = sprand(N, N, 0.5) \\ full(sprand(N, 1, 0.5) The code is giving us some solutions. For N=10000 memory runs out of my laptop machine. What are my options if I want to go, for example, N=10000000, assumed that …

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## [Bug in DistributedArrays?](https://discourse.julialang.org/t/bug-in-distributedarrays/12507)

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**Author:** [@raminammour](https://discourse.julialang.org/u/raminammour)\
**Replies:** 4\
**Last updated:** [July 20, 2018, 2:50pm UTC](https://discourse.julialang.org/t/bug-in-distributedarrays/12507 "2018-07-20T14:50:07Z")

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Hello all, I encountered this in an application and it took forever to debug. I think this is a bug in DistributedArrays on v0.6.4. MWE: julia\> addprocs(2) 2-element Array{Int64,1}: 2 3 julia\> using DistributedArray…

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## [Producer consumer pattern in julia](https://discourse.julialang.org/t/producer-consumer-pattern-in-julia/12421)

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**Author:** [@atteson](https://discourse.julialang.org/u/atteson)\
**Replies:** 2\
**Last updated:** [July 17, 2018, 3:38am UTC](https://discourse.julialang.org/t/producer-consumer-pattern-in-julia/12421 "2018-07-17T03:38:51Z")

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I’m implementing a producer consumer pattern in julia. Each producer will be pushing things on a queue and each consumer will be poping them off. I’d like each producer and each consumer to run in a different execution…

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## [Optimistic Concurrency Control](https://discourse.julialang.org/t/optimistic-concurrency-control/12402)

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**Author:** [@SohamTamb](https://discourse.julialang.org/u/SohamTamb)\
**Replies:** 2\
**Last updated:** [July 16, 2018, 1:12am UTC](https://discourse.julialang.org/t/optimistic-concurrency-control/12402 "2018-07-16T01:12:32Z")

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I am considering implementing a parallel (multi-threaded) algorithm using optimistic concurrency control. i.e. you allow race conditions to happen but ensure the correctness is not affected. I was hoping to find informa…

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## [Atomic Operations are too expensive.](https://discourse.julialang.org/t/atomic-operations-are-too-expensive/11827)

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**Author:** [@SohamTamb](https://discourse.julialang.org/u/SohamTamb)\
**Replies:** 3\
**Last updated:** [June 20, 2018, 4:53pm UTC](https://discourse.julialang.org/t/atomic-operations-are-too-expensive/11827 "2018-06-20T16:53:44Z")

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Are atomic operations supposed to be this costly? Is memory and allocations required for simple read/write operations? julia\> a = Atomic{Int64}(0) Atomic{Int64}(0) julia\> @btime a\[\] 100.546 ns (1 allocation: 16 byte…

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## [Basic Task Cooperation with Locks](https://discourse.julialang.org/t/basic-task-cooperation-with-locks/11186)

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**Author:** [@iwelch](https://discourse.julialang.org/u/iwelch)\
**Replies:** 0\
**Last updated:** [May 27, 2018, 6:36pm UTC](https://discourse.julialang.org/t/basic-task-cooperation-with-locks/11186 "2018-05-27T18:36:18Z")

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Dear Julia wizards: I understand that parallelism is still a work in progress, but I would like to know how to sketch the following code. My code wants to maintain a shared (int) vector of what each CPU core is and/or …

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## [Pmap with in place functions](https://discourse.julialang.org/t/pmap-with-in-place-functions/10523)

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**Author:** [@gideonsimpson](https://discourse.julialang.org/u/gideonsimpson)\
**Replies:** 10\
**Last updated:** [May 15, 2018, 9:58pm UTC](https://discourse.julialang.org/t/pmap-with-in-place-functions/10523 "2018-05-15T21:58:54Z")

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I was hoping to use pmap with an in place function, but I’m finding the behavior is not as expected. This example illustrates the issue: addprocs(2); @everywhere function f!(x) @. x+= randn(); x end X = \[zeros…

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