hash_to_hex_algop() returns a static buffer, relieving callers from the
responsibility of freeing memory after use. But the current
implementation uses the same static data for all threads and, thus, is
not thread-safe. We could avoid using this function and its wrappers
in threaded code, but they are sometimes too deep in the call stack to
be noticed or even avoided.
grep.c:grep_source_load_oid(), for example, uses the thread-unsafe
oid_to_hex() (on errors) despite being called in threaded code. And
oid_to_hex() -- which calls hash_to_hex_algop() -- is used in many other
places, as well:
$ git grep 'oid_to_hex(' | wc -l
818
Although hash_to_hex_algop() and its wrappers don't seem to be causing
problems out there for now (at least not reported), making them
thread-safe makes the codebase more robust against race conditions. We
can easily do that by replicating the static buffer in each thread's
local storage.
Original-patch-by: Fredrik Kuivinen <frekui@xxxxxxxxx>
Signed-off-by: Fredrik Kuivinen <frekui@xxxxxxxxx>
Signed-off-by: Matheus Tavares <matheus.bernardino@xxxxxx>
---
hex.c | 46 ++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 42 insertions(+), 4 deletions(-)
diff --git a/hex.c b/hex.c
index da51e64929..4f2f163d5e 100644
--- a/hex.c
+++ b/hex.c
@@ -1,4 +1,5 @@
#include "cache.h"
+#include "thread-utils.h"
const signed char hexval_table[256] = {
-1, -1, -1, -1, -1, -1, -1, -1, /* 00-07 */
@@ -136,12 +137,49 @@ char *oid_to_hex_r(char *buffer, const struct object_id *oid)
return hash_to_hex_algop_r(buffer, oid->hash, the_hash_algo);
}
+struct hexbuf_array {
+ int idx;
+ char bufs[4][GIT_MAX_HEXSZ + 1];
+};
+
+#ifdef HAVE_THREADS
+static pthread_key_t hexbuf_array_key;
+static pthread_once_t hexbuf_array_once = PTHREAD_ONCE_INIT;
+
+static void init_hexbuf_array_key(void)
+{
+ if (pthread_key_create(&hexbuf_array_key, free))
+ die(_("failed to initialize threads' key for hash to hex conversion"));
+}
+
+#else
+static struct hexbuf_array default_hexbuf_array;
+#endif
+
char *hash_to_hex_algop(const unsigned char *hash, const struct git_hash_algo *algop)
{
- static int bufno;
- static char hexbuffer[4][GIT_MAX_HEXSZ + 1];
- bufno = (bufno + 1) % ARRAY_SIZE(hexbuffer);
- return hash_to_hex_algop_r(hexbuffer[bufno], hash, algop);
+ struct hexbuf_array *ha;
+
+#ifdef HAVE_THREADS
+ void *value;
+
+ if (pthread_once(&hexbuf_array_once, init_hexbuf_array_key))
+ die(_("failed to initialize threads' key for hash to hex conversion"));
+
+ value = pthread_getspecific(hexbuf_array_key);
+ if (value) {
+ ha = (struct hexbuf_array *) value;
+ } else {
+ ha = xmalloc(sizeof(*ha));
+ if (pthread_setspecific(hexbuf_array_key, (void *)ha))
+ die(_("failed to set thread buffer for hash to hex conversion"));
+ }
+#else
+ ha = &default_hexbuf_array;
+#endif
+
+ ha->idx = (ha->idx + 1) % ARRAY_SIZE(ha->bufs);
+ return hash_to_hex_algop_r(ha->bufs[ha->idx], hash, algop);
}
char *hash_to_hex(const unsigned char *hash)
--
2.26.2
