From d4a5bc4efc40e090bf55a1a9221b6ab26b17b302 Mon Sep 17 00:00:00 2001
From: Tom Wang <tomcwang@fb.com>
Date: Fri, 29 Jul 2022 12:51:58 -0700
Subject: [PATCH] Add warning when multi-thread decompression is requested
 (#3208)

When user pass in argument for both decompression and multi-thread, print a warning message
to indicate that multi-threaded decompression is not supported.

* Add warning when multi-thread decompression is requested
* add test case for multi-threaded decoding warning
   Expectation is for -d -T0 we will not throw any warning,
   and see warning for any other -d -T(>1) inputs
---
 programs/zstdcli.c                                         | 3 +++
 tests/cli-tests/compression/multi-threaded.sh              | 4 ++++
 tests/cli-tests/compression/multi-threaded.sh.stderr.exact | 1 +
 3 files changed, 8 insertions(+)
 create mode 100644 tests/cli-tests/compression/multi-threaded.sh.stderr.exact

diff --git a/programs/zstdcli.c b/programs/zstdcli.c
index fbacb908a..372b7d7a3 100644
--- a/programs/zstdcli.c
+++ b/programs/zstdcli.c
@@ -1226,6 +1226,9 @@ int main(int argCount, const char* argv[])
     DISPLAYLEVEL(3, WELCOME_MESSAGE);
 
 #ifdef ZSTD_MULTITHREAD
+    if ((operation==zom_decompress) && (!singleThread) && (nbWorkers > 1)) {
+        DISPLAYLEVEL(2, "Warning : decompression does not support multi-threading\n");
+    }
     if ((nbWorkers==0) && (!singleThread)) {
         /* automatically set # workers based on # of reported cpus */
         if (defaultLogicalCores) {
diff --git a/tests/cli-tests/compression/multi-threaded.sh b/tests/cli-tests/compression/multi-threaded.sh
index e3961330a..bd01448e2 100755
--- a/tests/cli-tests/compression/multi-threaded.sh
+++ b/tests/cli-tests/compression/multi-threaded.sh
@@ -9,3 +9,7 @@ zstd --rsyncable -f file                ; zstd -t file.zst
 zstd -T0 -f file                        ; zstd -t file.zst
 zstd -T0 --auto-threads=logical -f file ; zstd -t file.zst
 zstd -T0 --auto-threads=physical -f file; zstd -t file.zst
+
+# multi-thread decompression warning test
+zstd -T0 -f file                        ; zstd -t file.zst; zstd -T0 -d file.zst -o file3
+zstd -T0 -f file                        ; zstd -t file.zst; zstd -T2 -d file.zst -o file4
diff --git a/tests/cli-tests/compression/multi-threaded.sh.stderr.exact b/tests/cli-tests/compression/multi-threaded.sh.stderr.exact
new file mode 100644
index 000000000..54d47d8bd
--- /dev/null
+++ b/tests/cli-tests/compression/multi-threaded.sh.stderr.exact
@@ -0,0 +1 @@
+Warning : decompression does not support multi-threading