计算在一个新的线程，并参考结果以后在R [英] Compute in a new thread and refer to results later in R

问题描述

在clojure中，我可以这样做：

In clojure I can do something like this:

(def x 
  ;; perform some expensive computation in a new thread
  ;; the repl is not blocked, so you can go on do something else
  (future 
    (do 
      (Thread/sleep 500) 
      3.14)))
;; ... do something else
;; now when you need x
;; just deref the future, get 3.14
@x    

？

推荐答案

在Linux上，您可以分叉一个进程，然后再收集它，如帮助页面？parallel :: mccollect（）;这是一个黑客，而不是像未来一样的强大功能。

On Linux you can fork a process and then collect it later, as illustrated on the help page ?parallel::mccollect(); this is more of a hack than a robust feature like future.

> p <- mcparallel({ Sys.sleep(5); "done" })
> sqrt(1:5)
[1] 1.000000 1.414214 1.732051 2.000000 2.236068
> mccollect(p)
$`15666`
[1] "done"

snow :: sendCall（） / snow :: recvResult（）请参见 snow :: clusterCall（）的实现，并注意集群可以是子集，例如 cl [1] 设置单个节点工作。

One can implement a similar strategy with snow::sendCall() / snow::recvResult(); see the implementation of snow::clusterCall() and note that a cluster can be subset, e.g., cl[1] to set a single node to work. (identically named functions are available in the parallel package, but not exported).

要检查作业是否已完成，请使用 wait = FALSE 。示例：

To check whether a job has finished, use wait = FALSE. Example:

require(parallel)
p1 = mcparallel({Sys.sleep(90); list(tag = "job1", res = 1})
p2 = mcparallel({Sys.sleep(80); 2})
p3 = mcparallel({Sys.sleep(60); 3})
res = mccollect(list(p1, p2, p3), wait = FALSE)
is.null(res)

如果这3个作业都没有完成，则 res 为NULL。

If none of these 3 jobs has been finished, then res is NULL.

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