Make the loop iterating over multiple parquet files parallel (#5486)

This makes the loop over multiple parquet files parallel

This PR is the same as #4952,
except it fixes the bug exposed by that PR. `CPtrsToData` and
`CPtrsToWhereNulls` need to be local for each parallel task, so they
must be declared inside of the forall loop. Technically, they will be
instantiated more than they really need to be, but it is correct.

Resolves #4952

Signed-off-by: Jade Abraham <jade.abraham@hpe.com>

Author: jabraham17

src/ParquetMsg.chpl

@@ -1281,20 +1281,24 @@ module ParquetMsg {
 
       var subdoms = getSubdomains(this.sizes);
 
+      pqLogger.debug(getM(), getR(), getL(),
+        "readInto with e.domain=%?, ty=%?, offsets=%?, subdoms=%?, filenames=%?"
+        .format(e.domain, this.ty, this.offsets, subdoms, this.filenames));
+
       coforall loc in Locales with (ref this) do on loc {
         const LocTypes = this.ty;
-        var CPtrsToData: [e.domain] c_ptr(void);
-        var CPtrsToWhereNulls: [e.domain] c_ptr(void);
 
         const ref DataDom = getDomain(e);
 
-        for (off, filedom, filename) in zip(this.offsets, subdoms, this.filenames) {
+        forall (off, filedom, filename) in zip(this.offsets, subdoms, this.filenames) with (ref this) {
+          var CPtrsToData: [e.domain] c_ptr(void);
+          var CPtrsToWhereNulls: [e.domain] c_ptr(void);
           for locdom in DataDom.localSubdomains() {
             const intersection = domain_intersection(locdom, filedom);
             if intersection.size > 0 {
               for colIdx in e.domain {
                 pqLogger.debug(getM(), getR(), getL(), "Locale " + here.id:string +
-                               " will read " + intersection:string);
+                               " will read " + intersection:string, " for column " + colIdx:string);
                 pqLogger.debug(getM(), getR(), getL(), "\tCTypes %?\n".format(LocTypes));
                 pqLogger.debug(getM(), getR(), getL(), "\tnullMode %?\n".format(nullMode));
                 CPtrsToData[colIdx] = getPtr(e=e[colIdx],
@@ -1308,6 +1312,9 @@ module ParquetMsg {
               }
 
               var pqErr = new parquetErrorMsg();
+              const startIdx = intersection.low - off;
+              pqLogger.debug(getM(), getR(), getL(), "about to call c_readAllCols for locale %? with filename=%?, startIdx=%?, ptrs=%?"
+                             .format(here.id, filename, startIdx, CPtrsToData));
               if c_readAllCols(filename.localize().c_str(),
                                c_ptrTo(CPtrsToData), c_ptrToConst(LocTypes),
                                c_ptrTo(CPtrsToWhereNulls),