If two threads have one freshly initialized string buffer each and call
strbuf_reset on them at roughly the same time, both threads will be
writing a '\0' to strbuf_slopbuf. That is not a problem in practice
since it doesn't matter in which order the writes happen. But
ThreadSanitizer will consider this a race.
When compiling with GIT_THREAD_SANITIZER, avoid writing to
strbuf_slopbuf. Let's instead assert on the first byte of strbuf_slopbuf
being '\0', since it ensures the promised invariant of "buf[len] ==
'\0'". (Writing to strbuf_slopbuf is normally bad, but could become even
more bad if we stop covering it up in strbuf_reset.)
Signed-off-by: Martin Ågren <martin.agren@xxxxxxxxx>
---
strbuf.h | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/strbuf.h b/strbuf.h
index e705b94db..295654d39 100644
--- a/strbuf.h
+++ b/strbuf.h
@@ -153,7 +153,19 @@ static inline void strbuf_setlen(struct strbuf *sb, size_t len)
/**
* Empty the buffer by setting the size of it to zero.
*/
+#ifdef GIT_THREAD_SANITIZER
+#define strbuf_reset(sb) \
+ do { \
+ struct strbuf *_sb = sb; \
+ _sb->len = 0; \
+ if (_sb->buf == strbuf_slopbuf) \
+ assert(!strbuf_slopbuf[0]); \
+ else \
+ _sb->buf[0] = '\0'; \
+ } while (0)
+#else
#define strbuf_reset(sb) strbuf_setlen(sb, 0)
+#endif
/**
--
2.14.1.151.gdfeca7a7e
