From 2e918d09ad01cc83911eac7147c3d7d8c7f6bd9a Mon Sep 17 00:00:00 2001
From: Lasse Collin <lasse.collin@tukaani.org>
Date: Thu, 3 Apr 2025 14:34:42 +0300
Subject: [PATCH] liblzma: mt dec: Fix lack of parallelization in single-shot
decoding
Single-shot decoding means calling lzma_code() by giving it the whole
input at once and enough output buffer space to store the uncompressed
data, and combining this with LZMA_FINISH and no timeout
(lzma_mt.timeout = 0). This way the file is decoded with a single
lzma_code() call if possible.
The bug prevented the decoder from starting more than one worker thread
in single-shot mode. The issue was noticed when reviewing the code;
there are no bug reports. Thus maybe few have tried this mode.
Fixes: 64b6d496dc81 ("liblzma: Threaded decoder: Always wait for output if LZMA_FINISH is used.")
(cherry picked from commit 0c80045ab82c406858d9d5bcea9f48ebc3d0a81d)
---
src/liblzma/common/stream_decoder_mt.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/src/liblzma/common/stream_decoder_mt.c b/src/liblzma/common/stream_decoder_mt.c
index 0cdb47d3..5da9a275 100644
--- a/src/liblzma/common/stream_decoder_mt.c
+++ b/src/liblzma/common/stream_decoder_mt.c
@@ -1543,10 +1543,17 @@ stream_decode_mt(void *coder_ptr, const lzma_allocator *allocator,
// Read output from the output queue. Just like in
// SEQ_BLOCK_HEADER, we wait to fill the output buffer
// only if waiting_allowed was set to true in the beginning
- // of this function (see the comment there).
+ // of this function (see the comment there) and there is
+ // no input available. In SEQ_BLOCK_HEADER, there is never
+ // input available when read_output_and_wait() is called,
+ // but here there can be when LZMA_FINISH is used, thus we
+ // need to check if *in_pos == in_size. Otherwise we would
+ // wait here instead of using the available input to start
+ // a new thread.
return_if_error(read_output_and_wait(coder, allocator,
out, out_pos, out_size,
- NULL, waiting_allowed,
+ NULL,
+ waiting_allowed && *in_pos == in_size,
&wait_abs, &has_blocked));
if (coder->pending_error != LZMA_OK) {