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Accepted
k_g
Asked: 2024-04-18 00:08:58 +0800 CST

Julia pmap 实际上没有使用多线程？

  • 772

我在跑

julia --threads 4

然后是命令

using Distributed
@time pmap(x->begin println(x); sleep(1); println(x); x end, 1:10);

我得到输出

1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
10
10
 10.766960 seconds (2.50 M allocations: 140.642 MiB, 0.20% gc time, 6.88% compilation time)

这清楚地表明这是串行运行的。为什么代码不能并行运行？

parallel-processing

1 个回答

  1. Best Answer

    并发任务数设置为nworkers()，比 少 1 nprocs()，这不是基于线程数，而是基于 Julia 启动的进程数，可以使用-p或进行设置--procs。

    $ julia --procs auto  # set to num logical cores; can also be an explicit number

    julia> using Distributed

julia> nworkers()
4

julia> @time pmap(x->begin println(x); sleep(1); println(x); x end, 1:10);
      From worker 5:    2
      From worker 2:    3
      From worker 3:    1
      From worker 4:    4
      From worker 3:    1
      From worker 5:    2
      From worker 4:    4
      From worker 2:    3
      From worker 4:    7
      From worker 5:    5
      From worker 3:    6
      From worker 2:    8
      From worker 5:    5
      From worker 4:    7
      From worker 5:    9
      From worker 3:    6
      From worker 2:    8
      From worker 4:    10
      From worker 5:    9
      From worker 4:    10
  3.047513 seconds (61.13 k allocations: 4.138 MiB, 1.12% compilation time)
    • 2

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