[Mesa-dev] [PATCH 3/3] util/disk_cache: use rand_xorshift128plus() to get our random int

[Timothy Arceri]

Otherwise for apps that don't seed the regular rand() we will always
remove old cache entries from the same dirs.
---
 src/util/disk_cache.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/util/disk_cache.c b/src/util/disk_cache.c
index f2d67c9..f6ecf0b 100644
--- a/src/util/disk_cache.c
+++ b/src/util/disk_cache.c
@@ -34,20 +34,21 @@
 #include <sys/statvfs.h>
 #include <sys/mman.h>
 #include <unistd.h>
 #include <fcntl.h>
 #include <pwd.h>
 #include <errno.h>
 #include <dirent.h>
 #include "zlib.h"
 
 #include "util/crc32.h"
+#include "util/rand_xor.h"
 #include "util/u_atomic.h"
 #include "util/u_queue.h"
 #include "util/mesa-sha1.h"
 #include "util/ralloc.h"
 #include "main/errors.h"
 #include "util/macros.h"
 
 #include "disk_cache.h"
 
 /* Number of bits to mask off from a cache key to get an index. */
@@ -354,20 +355,23 @@ disk_cache_create(const char *gpu_name, const char *timestamp)
    cache->max_size = max_size;
 
    /* A limit of 32 jobs was choosen as observations of Deus Ex start-up times
     * showed that we reached at most 11 jobs on an Intel i5-6400 CPU at 2.70GHz
     * (a fairly modest desktop CPU). 1 thread was chosen because we don't
     * really care about getting things to disk quickly just that it's not
     * blocking other tasks.
     */
    util_queue_init(&cache->cache_queue, "disk_cache", 32, 1);
 
+   /* Seed our rand function */
+   s_rand_xorshift128plus();
+
    ralloc_free(local);
 
    return cache;
 
  fail:
    if (fd != -1)
       close(fd);
    if (cache)
       ralloc_free(cache);
    ralloc_free(local);
@@ -569,22 +573,23 @@ evict_lru_item(struct disk_cache *cache)
    const char hex[] = "0123456789abcde";
    char *dir_path;
    int a, b;
    size_t size;
 
    /* With a reasonably-sized, full cache, (and with keys generated
     * from a cryptographic hash), we can choose two random hex digits
     * and reasonably expect the directory to exist with a file in it.
     * Provides pseudo-LRU eviction to reduce checking all cache files.
     */
-   a = rand() % 16;
-   b = rand() % 16;
+   uint64_t rand64 = rand_xorshift128plus();
+   a = (rand64 >> 32) % 16;
+   b = (rand64 & 0xFFFFFFFF) % 16;
 
    if (asprintf(&dir_path, "%s/%c%c", cache->path, hex[a], hex[b]) < 0)
       return;
 
    size = unlink_lru_file_from_directory(dir_path);
 
    free(dir_path);
 
    if (size) {
       p_atomic_add(cache->size, - (uint64_t)size);
-- 
2.9.3