feat: mp_wait4file macro

base/mp_wait4file.sas

@@ -0,0 +1,37 @@
+/**
+  @file
+  @brief Wait until a file arrives before continuing execution
+  @details Loops with a `sleep()` command until a file arrives or the max wait
+  period expires.
+
+  @example
+
+  Wait 3 minutes OR for /tmp/flag.txt to appear
+
+    %mp_wait4file(/tmp/flag.txt , maxwait=60*3)
+
+  @param [in] file The file to wait for.  Must be provided.
+  @param [in] maxwait= (0) Number of seconds to wait.  If set to zero, will
+    loop indefinitely (to a maximum of 46 days, per SAS [documentation](
+      https://support.sas.com/documentation/cdl/en/lrdict/64316/HTML/default/viewer.htm#a001418809.htm
+    )).  Otherwise, execution will proceed upon sleep expiry.
+  @param [in] interval= (1) The wait period between sleeps, in seconds
+
+
+**/
+
+%macro mp_wait4file(file, maxwait=0, interval=1);
+
+%if %str(&file)=%str() %then %do;
+  %put %str(ERR)OR: file not provided;
+%end;
+
+data _null_;
+  maxwait=&maxwait;
+  if maxwait=0 then maxwait=60*60*24*46;
+  do until (fileexist("&file") or slept>maxwait );
+    slept=sum(slept,sleep(&interval,1));
+  end;
+run;
+
+%mend mp_wait4file;