Async write for decompression (#2975)

* Async IO decompression:
- Added --[no-]asyncio flag for CLI decompression.
- Replaced dstBuffer in decompression with a pool of write jobs.
- Added an ability to execute write jobs in a separate thread.
- Added an ability to wait (join) on all jobs in a thread pool (queued and running).

tests/playTests.sh

@@ -1575,6 +1575,44 @@ elif [ "$longCSize19wlog23" -gt "$optCSize19wlog23" ]; then
     exit 1
 fi
 
+println "\n===>  zstd asyncio decompression tests "
+
+addFrame() {
+    datagen -g2M -s$2 >> tmp_uncompressed
+    datagen -g2M -s$2 | zstd --format=$1 >> tmp_compressed.zst
+}
+
+addTwoFrames() {
+  addFrame $1 1
+  addFrame $1 2
+}
+
+testAsyncIO() {
+  roundTripTest -g2M "3 --asyncio --format=$1"
+  roundTripTest -g2M "3 --no-asyncio --format=$1"
+}
+
+rm -f tmp_compressed tmp_uncompressed
+testAsyncIO zstd
+addTwoFrames zstd
+if [ $GZIPMODE -eq 1 ]; then
+  testAsyncIO gzip
+  addTwoFrames gzip
+fi
+if [ $LZMAMODE -eq 1 ]; then
+  testAsyncIO lzma
+  addTwoFrames lzma
+fi
+if [ $LZ4MODE -eq 1 ]; then
+  testAsyncIO lz4
+  addTwoFrames lz4
+fi
+cat tmp_uncompressed | $MD5SUM > tmp2
+zstd -d tmp_compressed.zst --asyncio -c | $MD5SUM > tmp1
+$DIFF -q tmp1 tmp2
+rm tmp1
+zstd -d tmp_compressed.zst --no-asyncio -c | $MD5SUM > tmp1
+$DIFF -q tmp1 tmp2
 
 if [ "$1" != "--test-large-data" ]; then
     println "Skipping large data tests"