This applies to AIX only.
Under UNIX, when a child process terminates, it signals to its parent that it has terminated and waits for the parent to acknowledge that signal. 4002⌶ is the mechanism to allow the APL programmer to issue such acknowledgements.
The result R is a matrix containing the list of the newly-terminated processes which have been terminated as a result of receiving the acknowledgement, along with information about each of those processes as described below.
R[;1] is the process ID (PID) of the terminated child
R[;2] is ¯1 if the child process terminated normally, otherwise it is the signal number which caused the child process to terminate.
R[;3] is ¯1 if the child process terminated as the result of a signal, otherwise it is the exit code of the child process
The remaining 15 columns are the contents of the rusage structure returned by the underlying wait3() system call. Note that the two timevalstructs are each returned as a floating point number.
The current rusage structure contains:
struct rusage {
struct timeval ru_utime; /* user time used */
struct timeval ru_stime; /* system time used */
long ru_maxrss; /* maximum resident set size */
long ru_ixrss; /* integral shared memory size */
long ru_idrss; /* integral unshared data size */
long ru_isrss; /* integral unshared stack size */
long ru_minflt; /* page reclaims */
long ru_majflt; /* page faults */
long ru_nswap; /* swaps */
long ru_inblock; /* block input operations */
long ru_oublock; /* block output operations */
long ru_msgsnd; /* messages sent */
long ru_msgrcv; /* messages received */
long ru_nsignals; /* signals received */
long ru_nvcsw; /* voluntary context switches */
long ru_nivcsw; /* involuntary context switches */
};
4002⌶ may return the PID of an abnormally terminated Auxiliary Processor; APL code should check that the list of processes that have been reaped is a superset of the list of processes that have been started.
Example
∇ tryforks;pid;fpid;rpid [1] rpids←fpids←⍬ [2] :For i :In ⍳5 [3] fpid←4000⌶'' ⍝ fork() a process [4] ⍝ if the child, hang around for a while [5] :If fpid=0 [6] ⎕DL 2×i [7] ⎕OFF [8] :Else [9] ⍝ if the parent, save child's pid [10] +fpids,←fpid [11] :EndIf [12] :EndFor [13] [14] :For i :In ⍳20 [15] ⎕DL 3 [16] ⍝ get list of newly terminated child processes [17] rpid←4002⌶'' [18] ⍝ and if not empty, make note of their pids [19] :If 0≠⊃⍴rpid [20] +rpids,←rpid[;1] [21] :EndIf [22] ⍝ if all fork()'d child processes accounted for [23] :If fpids≡fpids∩rpids [24] :Leave ⍝ quit [25] :EndIf [26] :EndFor ∇