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### `ox_select`

`ox_select(nlist[,timeout])`
  :: Returns the list of process identifiers on which data is available.

return
  list
nlist
  list of integers (process identifier)
timeout
  number

- Returns the list of process identifiers on which data is available.
- If all the processes in nlist are running, it blocks until one of the processes returns data. If timeout is specified, it waits for only timeout seconds.
- By sending `SM_popCMO` or `SM_popSerializedLocalObject` with `ox_push_cmd()` in advance and by examining the process status with `ox_select()`, one can avoid a hanging up caused by `ox_pop_local()` or `ox_pop_cmo()`. In such a case, data can be received by `ox_get()`.

    ox_launch();
    0
    [220] ox_launch();
    1
    [221] ox_launch();
    2
    [222] ox_rpc(2,"fctr",x^500-y^500);
    0
    [223] ox_rpc(1,"fctr",x^100-y^100);
    0
    [224] ox_rpc(0,"fctr",x^10-y^10);
    0
    [225] P=[0,1,2];
    [0,1,2]
    [226] map(ox_push_cmd,P,258);
    [0,0,0]
    [227] ox_select(P);
    [0]
    [228] ox_get(0);
    [[1,1],[x^4+y*x^3+y^2*x^2+y^3*x+y^4,1],
    [x^4-y*x^3+y^2*x^2-y^3*x+y^4,1],[x-y,1],[x+y,1]]

`References`
  section `ox_pop_cmo`, `ox_pop_local`, section `ox_push_cmd`, `ox_sync`, section `ox_get`

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