glsl: Add initial functions to implement an on-disk cache

This code provides for an on-disk cache of objects. Objects are stored
and retrieved via names that are arbitrary 20-byte sequences,
(intended to be SHA-1 hashes of something identifying for the
content). The directory used for the cache can be specified by means
of environment variables in the following priority order:

	$MESA_GLSL_CACHE_DIR
	$XDG_CACHE_HOME/mesa
	<user-home-directory>/.cache/mesa

By default the cache will be limited to a maximum size of 1GB. The
environment variable:

	$MESA_GLSL_CACHE_MAX_SIZE

can be set (at the time of GL context creation) to choose some other
size. This variable is a number that can optionally be followed by
'K', 'M', or 'G' to select a size in kilobytes, megabytes, or
gigabytes. By default, an unadorned value will be interpreted as
gigabytes.

The cache will be entirely disabled at runtime if the variable
MESA_GLSL_CACHE_DISABLE is set at the time of GL context creation.

Many thanks to Kristian Høgsberg <[email protected]> for the initial
implementation of code that led to this patch. In particular, the idea
of using an mmapped file, (indexed by a portion of the SHA-1), for the
efficent implementation of cache_has_key was entirely his
idea. Kristian also provided some very helpful advice in discussions
regarding various race conditions to be avoided in this code.

Signed-off-by: Timothy Arceri <[email protected]>
Reviewed-by: Eric Anholt <[email protected]>

1 files changed, 710 insertions, 0 deletions

diff --git a/src/compiler/glsl/cache.c b/src/compiler/glsl/cache.c
new file mode 100644
index 00000000000..64a34f06217
--- /dev/null
+++ b/src/compiler/glsl/cache.c
@@ -0,0 +1,710 @@
+/*
+ * Copyright © 2014 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include <ctype.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <sys/file.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/mman.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <pwd.h>
+#include <errno.h>
+#include <dirent.h>
+
+#include "util/u_atomic.h"
+#include "util/mesa-sha1.h"
+#include "util/ralloc.h"
+#include "main/errors.h"
+
+#include "cache.h"
+
+/* Number of bits to mask off from a cache key to get an index. */
+#define CACHE_INDEX_KEY_BITS 16
+
+/* Mask for computing an index from a key. */
+#define CACHE_INDEX_KEY_MASK ((1 << CACHE_INDEX_KEY_BITS) - 1)
+
+/* The number of keys that can be stored in the index. */
+#define CACHE_INDEX_MAX_KEYS (1 << CACHE_INDEX_KEY_BITS)
+
+struct program_cache {
+   /* The path to the cache directory. */
+   char *path;
+
+   /* A pointer to the mmapped index file within the cache directory. */
+   uint8_t *index_mmap;
+   size_t index_mmap_size;
+
+   /* Pointer to total size of all objects in cache (within index_mmap) */
+   uint64_t *size;
+
+   /* Pointer to stored keys, (within index_mmap). */
+   uint8_t *stored_keys;
+
+   /* Maximum size of all cached objects (in bytes). */
+   uint64_t max_size;
+};
+
+/* Create a directory named 'path' if it does not already exist.
+ *
+ * Returns: 0 if path already exists as a directory or if created.
+ *         -1 in all other cases.
+ */
+static int
+mkdir_if_needed(char *path)
+{
+   struct stat sb;
+
+   /* If the path exists already, then our work is done if it's a
+    * directory, but it's an error if it is not.
+    */
+   if (stat(path, &sb) == 0) {
+      if (S_ISDIR(sb.st_mode)) {
+         return 0;
+      } else {
+         _mesa_warning(NULL,
+                       "Cannot use %s for shader cache (not a directory)"
+                       "---disabling.\n", path);
+         return -1;
+      }
+   }
+
+   int ret = mkdir(path, 0755);
+   if (ret == 0 || (ret == -1 && errno == EEXIST))
+     return 0;
+
+   _mesa_warning(NULL,
+                 "Failed to create %s for shader cache (%s)---disabling.\n",
+                 path, strerror(errno));
+
+   return -1;
+}
+
+/* Concatenate an existing path and a new name to form a new path.  If the new
+ * path does not exist as a directory, create it then return the resulting
+ * name of the new path (ralloc'ed off of 'ctx').
+ *
+ * Returns NULL on any error, such as:
+ *
+ *      <path> does not exist or is not a directory
+ *      <path>/<name> exists but is not a directory
+ *      <path>/<name> cannot be created as a directory
+ */
+static char *
+concatenate_and_mkdir(void *ctx, char *path, char *name)
+{
+   char *new_path;
+   struct stat sb;
+
+   if (stat(path, &sb) != 0 || ! S_ISDIR(sb.st_mode))
+      return NULL;
+
+   new_path = ralloc_asprintf(ctx, "%s/%s", path, name);
+
+   if (mkdir_if_needed(new_path) == 0)
+      return new_path;
+   else
+      return NULL;
+}
+
+struct program_cache *
+cache_create(void)
+{
+   void *local;
+   struct program_cache *cache = NULL;
+   char *path, *max_size_str;
+   uint64_t max_size;
+   int fd = -1;
+   struct stat sb;
+   size_t size;
+
+   /* A ralloc context for transient data during this invocation. */
+   local = ralloc_context(NULL);
+   if (local == NULL)
+      goto fail;
+
+   /* At user request, disable shader cache entirely. */
+   if (getenv("MESA_GLSL_CACHE_DISABLE"))
+      goto fail;
+
+   /* Determine path for cache based on the first defined name as follows:
+    *
+    *   $MESA_GLSL_CACHE_DIR
+    *   $XDG_CACHE_HOME/mesa
+    *   <pwd.pw_dir>/.cache/mesa
+    */
+   path = getenv("MESA_GLSL_CACHE_DIR");
+   if (path && mkdir_if_needed(path) == -1) {
+      goto fail;
+   }
+
+   if (path == NULL) {
+      char *xdg_cache_home = getenv("XDG_CACHE_HOME");
+
+      if (xdg_cache_home) {
+         if (mkdir_if_needed(xdg_cache_home) == -1)
+            goto fail;
+
+         path = concatenate_and_mkdir(local, xdg_cache_home, "mesa");
+         if (path == NULL)
+            goto fail;
+      }
+   }
+
+   if (path == NULL) {
+      char *buf;
+      size_t buf_size;
+      struct passwd pwd, *result;
+
+      buf_size = sysconf(_SC_GETPW_R_SIZE_MAX);
+      if (buf_size == -1)
+         buf_size = 512;
+
+      /* Loop until buf_size is large enough to query the directory */
+      while (1) {
+         buf = ralloc_size(local, buf_size);
+
+         getpwuid_r(getuid(), &pwd, buf, buf_size, &result);
+         if (result)
+            break;
+
+         if (errno == ERANGE) {
+            ralloc_free(buf);
+            buf = NULL;
+            buf_size *= 2;
+         } else {
+            goto fail;
+         }
+      }
+
+      path = concatenate_and_mkdir(local, pwd.pw_dir, ".cache");
+      if (path == NULL)
+         goto fail;
+
+      path = concatenate_and_mkdir(local, path, "mesa");
+      if (path == NULL)
+         goto fail;
+   }
+
+   cache = ralloc(NULL, struct program_cache);
+   if (cache == NULL)
+      goto fail;
+
+   cache->path = ralloc_strdup(cache, path);
+   if (cache->path == NULL)
+      goto fail;
+
+   path = ralloc_asprintf(local, "%s/index", cache->path);
+   if (path == NULL)
+      goto fail;
+
+   fd = open(path, O_RDWR | O_CREAT | O_CLOEXEC, 0644);
+   if (fd == -1)
+      goto fail;
+
+   if (fstat(fd, &sb) == -1)
+      goto fail;
+
+   /* Force the index file to be the expected size. */
+   size = sizeof(*cache->size) + CACHE_INDEX_MAX_KEYS * CACHE_KEY_SIZE;
+   if (sb.st_size != size) {
+      if (ftruncate(fd, size) == -1)
+         goto fail;
+   }
+
+   /* We map this shared so that other processes see updates that we
+    * make.
+    *
+    * Note: We do use atomic addition to ensure that multiple
+    * processes don't scramble the cache size recorded in the
+    * index. But we don't use any locking to prevent multiple
+    * processes from updating the same entry simultaneously. The idea
+    * is that if either result lands entirely in the index, then
+    * that's equivalent to a well-ordered write followed by an
+    * eviction and a write. On the other hand, if the simultaneous
+    * writes result in a corrupt entry, that's not really any
+    * different than both entries being evicted, (since within the
+    * guarantees of the cryptographic hash, a corrupt entry is
+    * unlikely to ever match a real cache key).
+    */
+   cache->index_mmap = mmap(NULL, size, PROT_READ | PROT_WRITE,
+                            MAP_SHARED, fd, 0);
+   if (cache->index_mmap == MAP_FAILED)
+      goto fail;
+   cache->index_mmap_size = size;
+
+   close(fd);
+
+   cache->size = (uint64_t *) cache->index_mmap;
+   cache->stored_keys = cache->index_mmap + sizeof(uint64_t);
+
+   max_size = 0;
+
+   max_size_str = getenv("MESA_GLSL_CACHE_MAX_SIZE");
+   if (max_size_str) {
+      char *end;
+      max_size = strtoul(max_size_str, &end, 10);
+      if (end == max_size_str) {
+         max_size = 0;
+      } else {
+         while (*end && isspace(*end))
+            end++;
+         switch (*end) {
+         case 'K':
+         case 'k':
+            max_size *= 1024;
+            break;
+         case 'M':
+         case 'm':
+            max_size *= 1024*1024;
+            break;
+         case '\0':
+         case 'G':
+         case 'g':
+         default:
+            max_size *= 1024*1024*1024;
+            break;
+         }
+      }
+   }
+
+   /* Default to 1GB for maximum cache size. */
+   if (max_size == 0)
+      max_size = 1024*1024*1024;
+
+   cache->max_size = max_size;
+
+   ralloc_free(local);
+
+   return cache;
+
+ fail:
+   if (fd != -1)
+      close(fd);
+   if (cache)
+      ralloc_free(cache);
+   ralloc_free(local);
+
+   return NULL;
+}
+
+void
+cache_destroy(struct program_cache *cache)
+{
+   munmap(cache->index_mmap, cache->index_mmap_size);
+
+   ralloc_free(cache);
+}
+
+/* Return a filename within the cache's directory corresponding to 'key'. The
+ * returned filename is ralloced with 'cache' as the parent context.
+ *
+ * Returns NULL if out of memory.
+ */
+static char *
+get_cache_file(struct program_cache *cache, cache_key key)
+{
+   char buf[41];
+
+   _mesa_sha1_format(buf, key);
+
+   return ralloc_asprintf(cache, "%s/%c%c/%s",
+                          cache->path, buf[0], buf[1], buf + 2);
+}
+
+/* Create the directory that will be needed for the cache file for \key.
+ *
+ * Obviously, the implementation here must closely match
+ * _get_cache_file above.
+*/
+static void
+make_cache_file_directory(struct program_cache *cache, cache_key key)
+{
+   char *dir;
+   char buf[41];
+
+   _mesa_sha1_format(buf, key);
+
+   dir = ralloc_asprintf(cache, "%s/%c%c", cache->path, buf[0], buf[1]);
+
+   mkdir_if_needed(dir);
+
+   ralloc_free(dir);
+}
+
+/* Given a directory path and predicate function, count all entries in
+ * that directory for which the predicate returns true. Then choose a
+ * random entry from among those counted.
+ *
+ * Returns: A malloc'ed string for the path to the chosen file, (or
+ * NULL on any error). The caller should free the string when
+ * finished.
+ */
+static char *
+choose_random_file_matching(const char *dir_path,
+                            bool (*predicate)(struct dirent *))
+{
+   DIR *dir;
+   struct dirent *entry;
+   unsigned int count, victim;
+   char *filename;
+
+   dir = opendir(dir_path);
+   if (dir == NULL)
+      return NULL;
+
+   count = 0;
+
+   while (1) {
+      entry = readdir(dir);
+      if (entry == NULL)
+         break;
+      if (! predicate(entry))
+         continue;
+
+      count++;
+   }
+
+   if (count == 0) {
+      closedir(dir);
+      return NULL;
+   }
+
+   victim = rand() % count;
+
+   rewinddir(dir);
+   count = 0;
+
+   while (1) {
+      entry = readdir(dir);
+      if (entry == NULL)
+         break;
+      if (! predicate(entry))
+         continue;
+      if (count == victim)
+         break;
+
+      count++;
+   }
+
+   if (entry == NULL) {
+      closedir(dir);
+      return NULL;
+   }
+
+   asprintf(&filename, "%s/%s", dir_path, entry->d_name);
+
+   closedir(dir);
+
+   return filename;
+}
+
+/* Is entry a regular file, and not having a name with a trailing
+ * ".tmp"
+ */
+static bool
+is_regular_non_tmp_file(struct dirent *entry)
+{
+   size_t len;
+
+   if (entry->d_type != DT_REG)
+      return false;
+
+   len = strlen (entry->d_name);
+   if (len >= 4 && strcmp(&entry->d_name[len-4], ".tmp") == 0)
+      return false;
+
+   return true;
+}
+
+/* Returns the size of the deleted file, (or 0 on any error). */
+static size_t
+unlink_random_file_from_directory(const char *path)
+{
+   struct stat sb;
+   char *filename;
+
+   filename = choose_random_file_matching(path, is_regular_non_tmp_file);
+   if (filename == NULL)
+      return 0;
+
+   if (stat(filename, &sb) == -1) {
+      free (filename);
+      return 0;
+   }
+
+   unlink(filename);
+
+   free (filename);
+
+   return sb.st_size;
+}
+
+/* Is entry a directory with a two-character name, (and not the
+ * special name of "..")
+ */
+static bool
+is_two_character_sub_directory(struct dirent *entry)
+{
+   if (entry->d_type != DT_DIR)
+      return false;
+
+   if (strlen(entry->d_name) != 2)
+      return false;
+
+   if (strcmp(entry->d_name, "..") == 0)
+      return false;
+
+   return true;
+}
+
+static void
+evict_random_item(struct program_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.
+    */
+   a = rand() % 16;
+   b = rand() % 16;
+
+   asprintf (&dir_path, "%s/%c%c", cache->path, hex[a], hex[b]);
+   if (dir_path == NULL)
+      return;
+
+   size = unlink_random_file_from_directory(dir_path);
+
+   free(dir_path);
+
+   if (size) {
+      p_atomic_add(cache->size, - size);
+      return;
+   }
+
+   /* In the case where the random choice of directory didn't find
+    * something, we choose randomly from the existing directories.
+    *
+    * Really, the only reason this code exists is to allow the unit
+    * tests to work, (which use an artificially-small cache to be able
+    * to force a single cached item to be evicted).
+    */
+   dir_path = choose_random_file_matching(cache->path,
+                                          is_two_character_sub_directory);
+   if (dir_path == NULL)
+      return;
+
+   size = unlink_random_file_from_directory(dir_path);
+
+   free(dir_path);
+
+   if (size)
+      p_atomic_add(cache->size, - size);
+}
+
+void
+cache_put(struct program_cache *cache,
+          cache_key key,
+          const void *data,
+          size_t size)
+{
+   int fd = -1, fd_final = -1, err, ret;
+   size_t len;
+   char *filename = NULL, *filename_tmp = NULL;
+   const char *p = data;
+
+   filename = get_cache_file(cache, key);
+   if (filename == NULL)
+      goto done;
+
+   /* Write to a temporary file to allow for an atomic rename to the
+    * final destination filename, (to prevent any readers from seeing
+    * a partially written file).
+    */
+   filename_tmp = ralloc_asprintf(cache, "%s.tmp", filename);
+   if (filename_tmp == NULL)
+      goto done;
+
+   fd = open(filename_tmp, O_WRONLY | O_CLOEXEC | O_CREAT, 0644);
+
+   /* Make the two-character subdirectory within the cache as needed. */
+   if (fd == -1) {
+      if (errno != ENOENT)
+         goto done;
+
+      make_cache_file_directory(cache, key);
+
+      fd = open(filename_tmp, O_WRONLY | O_CLOEXEC | O_CREAT, 0644);
+      if (fd == -1)
+         goto done;
+   }
+
+   /* With the temporary file open, we take an exclusive flock on
+    * it. If the flock fails, then another process still has the file
+    * open with the flock held. So just let that file be responsible
+    * for writing the file.
+    */
+   err = flock(fd, LOCK_EX | LOCK_NB);
+   if (err == -1)
+      goto done;
+
+   /* Now that we have the lock on the open temporary file, we can
+    * check to see if the destination file already exists. If so,
+    * another process won the race between when we saw that the file
+    * didn't exist and now. In this case, we don't do anything more,
+    * (to ensure the size accounting of the cache doesn't get off).
+    */
+   fd_final = open(filename, O_RDONLY | O_CLOEXEC);
+   if (fd_final != -1)
+      goto done;
+
+   /* OK, we're now on the hook to write out a file that we know is
+    * not in the cache, and is also not being written out to the cache
+    * by some other process.
+    *
+    * Before we do that, if the cache is too large, evict something
+    * else first.
+    */
+   if (*cache->size + size > cache->max_size)
+      evict_random_item(cache);
+
+   /* Now, finally, write out the contents to the temporary file, then
+    * rename them atomically to the destination filename, and also
+    * perform an atomic increment of the total cache size.
+    */
+   for (len = 0; len < size; len += ret) {
+      ret = write(fd, p + len, size - len);
+      if (ret == -1) {
+         unlink(filename_tmp);
+         goto done;
+      }
+   }
+
+   rename(filename_tmp, filename);
+
+   p_atomic_add(cache->size, size);
+
+   /* This close finally releases the flock, (now that the final dile
+    * has been renamed into place and the size has been added).
+    */
+   close(fd);
+   fd = -1;
+
+ done:
+   if (filename_tmp)
+      ralloc_free(filename_tmp);
+   if (filename)
+      ralloc_free(filename);
+   if (fd != -1)
+      close(fd);
+}
+
+void *
+cache_get(struct program_cache *cache, cache_key key, size_t *size)
+{
+   int fd = -1, ret, len;
+   struct stat sb;
+   char *filename = NULL;
+   uint8_t *data = NULL;
+
+   if (size)
+      *size = 0;
+
+   filename = get_cache_file(cache, key);
+   if (filename == NULL)
+      goto fail;
+
+   fd = open(filename, O_RDONLY | O_CLOEXEC);
+   if (fd == -1)
+      goto fail;
+
+   if (fstat(fd, &sb) == -1)
+      goto fail;
+
+   data = malloc(sb.st_size);
+   if (data == NULL)
+      goto fail;
+
+   for (len = 0; len < sb.st_size; len += ret) {
+      ret = read(fd, data + len, sb.st_size - len);
+      if (ret == -1)
+         goto fail;
+   }
+
+   ralloc_free(filename);
+   close(fd);
+
+   if (size)
+      *size = sb.st_size;
+
+   return data;
+
+ fail:
+   if (data)
+      free(data);
+   if (filename)
+      ralloc_free(filename);
+   if (fd != -1)
+      close(fd);
+
+   return NULL;
+}
+
+void
+cache_put_key(struct program_cache *cache, cache_key key)
+{
+   uint32_t *key_chunk = (uint32_t *) key;
+   int i = *key_chunk & CACHE_INDEX_KEY_MASK;
+   unsigned char *entry;
+
+   entry = &cache->stored_keys[i + CACHE_KEY_SIZE];
+
+   memcpy(entry, key, CACHE_KEY_SIZE);
+}
+
+/* This function lets us test whether a given key was previously
+ * stored in the cache with cache_put_key(). The implement is
+ * efficient by not using syscalls or hitting the disk. It's not
+ * race-free, but the races are benign. If we race with someone else
+ * calling cache_put_key, then that's just an extra cache miss and an
+ * extra recompile.
+ */
+bool
+cache_has_key(struct program_cache *cache, cache_key key)
+{
+   uint32_t *key_chunk = (uint32_t *) key;
+   int i = *key_chunk & CACHE_INDEX_KEY_MASK;
+   unsigned char *entry;
+
+   entry = &cache->stored_keys[i + CACHE_KEY_SIZE];
+
+   return memcmp(entry, key, CACHE_KEY_SIZE) == 0;
+}