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 <krh@bitplanet.net> 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 <timothy.arceri@collabora.com>
Reviewed-by: Eric Anholt <eric@anholt.net>

7 files changed, 1316 insertions, 0 deletions

diff --git a/configure.ac b/configure.ac
index b9e6000a3d5..c702b539994 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1305,6 +1305,9 @@ if test "x$with_sha1" = "x"; then
     fi
 fi
 AM_CONDITIONAL([ENABLE_SHADER_CACHE], [test x$enable_shader_cache = xyes])
+if test "x$enable_shader_cache" = "xyes"; then
+   AC_DEFINE([ENABLE_SHADER_CACHE], [1], [Enable shader cache])
+fi
 
 case "$host_os" in
 linux*)
diff --git a/src/compiler/Makefile.glsl.am b/src/compiler/Makefile.glsl.am
index b8225cbe206..80dfb737fb2 100644
--- a/src/compiler/Makefile.glsl.am
+++ b/src/compiler/Makefile.glsl.am
@@ -33,6 +33,7 @@ EXTRA_DIST += glsl/tests glsl/glcpp/tests glsl/README	\
 TESTS += glsl/glcpp/tests/glcpp-test			\
 	glsl/glcpp/tests/glcpp-test-cr-lf		\
 	glsl/tests/blob-test				\
+	glsl/tests/cache-test				\
 	glsl/tests/general-ir-test			\
 	glsl/tests/optimization-test			\
 	glsl/tests/sampler-types-test			\
@@ -47,6 +48,7 @@ check_PROGRAMS +=					\
 	glsl/glcpp/glcpp				\
 	glsl/glsl_test					\
 	glsl/tests/blob-test				\
+	glsl/tests/cache-test				\
 	glsl/tests/general-ir-test			\
 	glsl/tests/sampler-types-test			\
 	glsl/tests/uniform-initializer-test
@@ -58,6 +60,11 @@ glsl_tests_blob_test_SOURCES =				\
 glsl_tests_blob_test_LDADD =				\
 	glsl/libglsl.la
 
+glsl_tests_cache_test_SOURCES =				\
+	glsl/tests/cache_test.c
+glsl_tests_cache_test_LDADD =				\
+	glsl/libglsl.la
+
 glsl_tests_general_ir_test_SOURCES =			\
 	glsl/tests/builtin_variable_test.cpp		\
 	glsl/tests/invalidate_locations_test.cpp	\
@@ -120,6 +127,9 @@ glsl_libglsl_la_SOURCES =				\
 	$(LIBGLSL_GENERATED_FILES)			\
 	$(LIBGLSL_FILES)
 
+if ENABLE_SHADER_CACHE
+glsl_libglsl_la_SOURCES += $(LIBGLSL_SHADER_CACHE_FILES)
+endif
 
 glsl_libstandalone_la_SOURCES = \
 	$(GLSL_COMPILER_CXX_FILES)
diff --git a/src/compiler/Makefile.sources b/src/compiler/Makefile.sources
index f5b4f9c0b98..712b33aa74c 100644
--- a/src/compiler/Makefile.sources
+++ b/src/compiler/Makefile.sources
@@ -136,6 +136,10 @@ LIBGLSL_FILES = \
 	glsl/s_expression.cpp \
 	glsl/s_expression.h
 
+LIBGLSL_SHADER_CACHE_FILES = \
+	glsl/cache.c \
+	glsl/cache.h
+
 # glsl_compiler
 
 GLSL_COMPILER_CXX_FILES = \
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;
+}
diff --git a/src/compiler/glsl/cache.h b/src/compiler/glsl/cache.h
new file mode 100644
index 00000000000..78df32b6c54
--- /dev/null
+++ b/src/compiler/glsl/cache.h
@@ -0,0 +1,172 @@
+/*
+ * 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.
+ */
+
+#pragma once
+#ifndef CACHE_H
+#define CACHE_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <stdint.h>
+#include <stdbool.h>
+
+/* Size of cache keys in bytes. */
+#define CACHE_KEY_SIZE 20
+
+typedef uint8_t cache_key[CACHE_KEY_SIZE];
+
+/* Provide inlined stub functions if the shader cache is disabled. */
+
+#ifdef ENABLE_SHADER_CACHE
+
+/**
+ * Create a new cache object.
+ *
+ * This function creates the handle necessary for all subsequent cache_*
+ * functions.
+ *
+ * This cache provides two distinct operations:
+ *
+ *   o Storage and retrieval of arbitrary objects by cryptographic
+ *     name (or "key").  This is provided via cache_put() and
+ *     cache_get().
+ *
+ *   o The ability to store a key alone and check later whether the
+ *     key was previously stored. This is provided via cache_put_key()
+ *     and cache_has_key().
+ *
+ * The put_key()/has_key() operations are conceptually identical to
+ * put()/get() with no data, but are provided separately to allow for
+ * a more efficient implementation.
+ *
+ * In all cases, the keys are sequences of 20 bytes. It is anticipated
+ * that callers will compute appropriate SHA-1 signatures for keys,
+ * (though nothing in this implementation directly relies on how the
+ * names are computed). See mesa-sha1.h and _mesa_sha1_compute for
+ * assistance in computing SHA-1 signatures.
+ */
+struct program_cache *
+cache_create(void);
+
+/**
+ * Destroy a cache object, (freeing all associated resources).
+ */
+void
+cache_destroy(struct program_cache *cache);
+
+/**
+ * Store an item in the cache under the name \key.
+ *
+ * The item can be retrieved later with cache_get(), (unless the item has
+ * been evicted in the interim).
+ *
+ * Any call to cache_put() may cause an existing, random item to be
+ * evicted from the cache.
+ */
+void
+cache_put(struct program_cache *cache, cache_key key,
+          const void *data, size_t size);
+
+/**
+ * Retrieve an item previously stored in the cache with the name <key>.
+ *
+ * The item must have been previously stored with a call to cache_put().
+ *
+ * If \size is non-NULL, then, on successful return, it will be set to the
+ * size of the object.
+ *
+ * \return A pointer to the stored object if found. NULL if the object
+ * is not found, or if any error occurs, (memory allocation failure,
+ * filesystem error, etc.). The returned data is malloc'ed so the
+ * caller should call free() it when finished.
+ */
+void *
+cache_get(struct program_cache *cache, cache_key key, size_t *size);
+
+/**
+ * Store the name \key within the cache, (without any associated data).
+ *
+ * Later this key can be checked with cache_has_key(), (unless the key
+ * has been evicted in the interim).
+ *
+ * Any call to cache_record() may cause an existing, random key to be
+ * evicted from the cache.
+ */
+void
+cache_put_key(struct program_cache *cache, cache_key key);
+
+/**
+ * Test whether the name \key was previously recorded in the cache.
+ *
+ * Return value: True if cache_put_key() was previously called with
+ * \key, (and the key was not evicted in the interim).
+ *
+ * Note: cache_has_key() will only return true for keys passed to
+ * cache_put_key(). Specifically, a call to cache_put() will not cause
+ * cache_has_key() to return true for the same key.
+ */
+bool
+cache_has_key(struct program_cache *cache, cache_key key);
+
+#else
+
+static inline struct program_cache *
+cache_create(void)
+{
+   return NULL;
+}
+
+static inline void
+cache_put(struct program_cache *cache, cache_key key,
+          const void *data, size_t size)
+{
+   return;
+}
+
+static inline uint8_t *
+cache_get(struct program_cache *cache, cache_key key, size_t *size)
+{
+   return NULL;
+}
+
+static inline void
+cache_put_key(struct program_cache *cache, cache_key key)
+{
+   return;
+}
+
+static inline bool
+cache_has_key(struct program_cache *cache, cache_key key)
+{
+   return false;
+}
+
+#endif /* ENABLE_SHADER_CACHE */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* CACHE_H */
diff --git a/src/compiler/glsl/tests/.gitignore b/src/compiler/glsl/tests/.gitignore
index 13dcdc4ab73..1661ae78bdd 100644
--- a/src/compiler/glsl/tests/.gitignore
+++ b/src/compiler/glsl/tests/.gitignore
@@ -1,4 +1,5 @@
 blob-test
+cache-test
 ralloc-test
 uniform-initializer-test
 sampler-types-test
diff --git a/src/compiler/glsl/tests/cache_test.c b/src/compiler/glsl/tests/cache_test.c
new file mode 100644
index 00000000000..1b0403caca6
--- /dev/null
+++ b/src/compiler/glsl/tests/cache_test.c
@@ -0,0 +1,416 @@
+/*
+ * Copyright © 2015 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.
+ */
+
+/* A collection of unit tests for cache.c */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <ftw.h>
+#include <errno.h>
+#include <stdarg.h>
+
+#include "util/mesa-sha1.h"
+#include "cache.h"
+
+bool error = false;
+
+void
+_mesa_warning(void *ctx, const char *fmt, ...);
+
+void
+_mesa_warning(void *ctx, const char *fmt, ...)
+{
+    va_list vargs;
+    (void) ctx;
+
+    va_start(vargs, fmt);
+
+    /* This output is not thread-safe, but that's good enough for the
+     * standalone compiler.
+     */
+    fprintf(stderr, "Mesa warning: ");
+    vfprintf(stderr, fmt, vargs);
+    fprintf(stderr, "\n");
+
+    va_end(vargs);
+}
+
+static void
+expect_equal(uint64_t actual, uint64_t expected, const char *test)
+{
+   if (actual != expected) {
+      fprintf(stderr, "Error: Test '%s' failed: Expected=%ld, Actual=%ld\n",
+              test, expected, actual);
+      error = true;
+   }
+}
+
+static void
+expect_null(void *ptr, const char *test)
+{
+   if (ptr != NULL) {
+      fprintf(stderr, "Error: Test '%s' failed: Result=%p, but expected NULL.\n",
+              test, ptr);
+      error = true;
+   }
+}
+
+static void
+expect_non_null(void *ptr, const char *test)
+{
+   if (ptr == NULL) {
+      fprintf(stderr, "Error: Test '%s' failed: Result=NULL, but expected something else.\n",
+              test);
+      error = true;
+   }
+}
+
+static void
+expect_equal_str(const char *actual, const char *expected, const char *test)
+{
+   if (strcmp(actual, expected)) {
+      fprintf(stderr, "Error: Test '%s' failed:\n\t"
+              "Expected=\"%s\", Actual=\"%s\"\n",
+              test, expected, actual);
+      error = true;
+   }
+}
+
+/* Callback for nftw used in rmrf_local below.
+ */
+static int
+remove_entry(const char *path,
+             const struct stat *sb,
+             int typeflag,
+             struct FTW *ftwbuf)
+{
+   int err = remove(path);
+
+   if (err)
+      fprintf(stderr, "Error removing %s: %s\n", path, strerror(errno));
+
+   return err;
+}
+
+/* Recursively remove a directory.
+ *
+ * This is equivalent to "rm -rf <dir>" with one bit of protection
+ * that the directory name must begin with "." to ensure we don't
+ * wander around deleting more than intended.
+ *
+ * Returns 0 on success, -1 on any error.
+ */
+static int
+rmrf_local(const char *path)
+{
+   if (path == NULL || *path == '\0' || *path != '.')
+      return -1;
+
+   return nftw(path, remove_entry, 64, FTW_DEPTH | FTW_PHYS | FTW_MOUNT);
+}
+
+#define CACHE_TEST_TMP "./cache-test-tmp"
+
+static void
+test_cache_create(void)
+{
+   struct program_cache *cache;
+   int err;
+
+   /* Before doing anything else, ensure that with
+    * MESA_GLSL_CACHE_DISABLE set, that cache_create returns NULL.
+    */
+   setenv("MESA_GLSL_CACHE_DISABLE", "1", 1);
+   cache = cache_create();
+   expect_null(cache, "cache_create with MESA_GLSL_CACHE_DISABLE set");
+
+   unsetenv("MESA_GLSL_CACHE_DISABLE");
+
+   /* For the first real cache_create() clear these environment
+    * variables to test creation of cache in home directory.
+    */
+   unsetenv("MESA_GLSL_CACHE_DIR");
+   unsetenv("XDG_CACHE_HOME");
+
+   cache = cache_create();
+   expect_non_null(cache, "cache_create with no environment variables");
+
+   cache_destroy(cache);
+
+   /* Test with XDG_CACHE_HOME set */
+   setenv("XDG_CACHE_HOME", CACHE_TEST_TMP "/xdg-cache-home", 1);
+   cache = cache_create();
+   expect_null(cache, "cache_create with XDG_CACHE_HOME set with"
+               "a non-existing parent directory");
+
+   mkdir(CACHE_TEST_TMP, 0755);
+   cache = cache_create();
+   expect_non_null(cache, "cache_create with XDG_CACHE_HOME set");
+
+   cache_destroy(cache);
+
+   /* Test with MESA_GLSL_CACHE_DIR set */
+   err = rmrf_local(CACHE_TEST_TMP);
+   expect_equal(err, 0, "Removing " CACHE_TEST_TMP);
+
+   setenv("MESA_GLSL_CACHE_DIR", CACHE_TEST_TMP "/mesa-glsl-cache-dir", 1);
+   cache = cache_create();
+   expect_null(cache, "cache_create with MESA_GLSL_CACHE_DIR set with"
+               "a non-existing parent directory");
+
+   mkdir(CACHE_TEST_TMP, 0755);
+   cache = cache_create();
+   expect_non_null(cache, "cache_create with MESA_GLSL_CACHE_DIR set");
+
+   cache_destroy(cache);
+}
+
+static bool
+does_cache_contain(struct program_cache *cache, cache_key key)
+{
+   void *result;
+
+   result = cache_get(cache, key, NULL);
+
+   if (result) {
+      free(result);
+      return true;
+   }
+
+   return false;
+}
+
+static void
+test_put_and_get(void)
+{
+   struct program_cache *cache;
+   /* If the text of this blob is changed, then blob_key_byte_zero
+    * also needs to be updated.
+    */
+   char blob[] = "This is a blob of thirty-seven bytes";
+   uint8_t blob_key[20];
+   uint8_t blob_key_byte_zero = 0xca;
+   char string[] = "While this string has thirty-four";
+   uint8_t string_key[20];
+   char *result;
+   size_t size;
+   uint8_t *one_KB, *one_MB;
+   uint8_t one_KB_key[20], one_MB_key[20];
+   int count;
+
+   cache = cache_create();
+
+   _mesa_sha1_compute(blob, sizeof(blob), blob_key);
+
+   /* Ensure that cache_get returns nothing before anything is added. */
+   result = cache_get(cache, blob_key, &size);
+   expect_null(result, "cache_get with non-existent item (pointer)");
+   expect_equal(size, 0, "cache_get with non-existent item (size)");
+
+   /* Simple test of put and get. */
+   cache_put(cache, blob_key, blob, sizeof(blob));
+
+   result = cache_get(cache, blob_key, &size);
+   expect_equal_str(blob, result, "cache_get of existing item (pointer)");
+   expect_equal(size, sizeof(blob), "cache_get of existing item (size)");
+
+   free(result);
+
+   /* Test put and get of a second item. */
+   _mesa_sha1_compute(string, sizeof(string), string_key);
+   cache_put(cache, string_key, string, sizeof(string));
+
+   result = cache_get(cache, string_key, &size);
+   expect_equal_str(result, string, "2nd cache_get of existing item (pointer)");
+   expect_equal(size, sizeof(string), "2nd cache_get of existing item (size)");
+
+   free(result);
+
+   /* Set the cache size to 1KB and add a 1KB item to force an eviction. */
+   cache_destroy(cache);
+
+   setenv("MESA_GLSL_CACHE_MAX_SIZE", "1K", 1);
+   cache = cache_create();
+
+   one_KB = calloc(1, 1024);
+
+   /* Obviously the SHA-1 hash of 1024 zero bytes isn't particularly
+    * interesting. But we do have want to take some special care with
+    * the hash we use here. The issue is that in this artificial case,
+    * (with only three files in the cache), the probability is good
+    * that each of the three files will end up in their own
+    * directory. Then, if the directory containing the .tmp file for
+    * the new item being added for cache_put() is the chosen victim
+    * directory for eviction, then no suitable file will be found and
+    * nothing will be evicted.
+    *
+    * That's actually expected given how the eviction code is
+    * implemented, (which expects to only evict once things are more
+    * interestingly full than that).
+    *
+    * For this test, we force this signature to land in the same
+    * directory as the original blob first written to the cache.
+    */
+   _mesa_sha1_compute(one_KB, 1024, one_KB_key);
+   one_KB_key[0] = blob_key_byte_zero;
+
+   cache_put(cache, one_KB_key, one_KB, 1024);
+
+   free(one_KB);
+
+   result = cache_get(cache, one_KB_key, &size);
+   expect_non_null(result, "3rd cache_get of existing item (pointer)");
+   expect_equal(size, 1024, "3rd cache_get of existing item (size)");
+
+   free(result);
+
+   /* Ensure eviction happened by checking that only one of the two
+    * previously-added items can still be fetched.
+    */
+   count = 0;
+   if (does_cache_contain(cache, blob_key))
+       count++;
+
+   if (does_cache_contain(cache, string_key))
+       count++;
+
+   expect_equal(count, 1, "cache_put eviction with MAX_SIZE=1K");
+
+   /* Now increase the size to 1M, add back both items, and ensure all
+    * three that have been added are available via cache_get.
+    */
+   cache_destroy(cache);
+
+   setenv("MESA_GLSL_CACHE_MAX_SIZE", "1M", 1);
+   cache = cache_create();
+
+   cache_put(cache, blob_key, blob, sizeof(blob));
+   cache_put(cache, string_key, string, sizeof(string));
+
+   count = 0;
+   if (does_cache_contain(cache, blob_key))
+       count++;
+
+   if (does_cache_contain(cache, string_key))
+       count++;
+
+   if (does_cache_contain(cache, one_KB_key))
+       count++;
+
+   expect_equal(count, 3, "no eviction before overflow with MAX_SIZE=1M");
+
+   /* Finally, check eviction again after adding an object of size 1M. */
+   one_MB = calloc(1024, 1024);
+
+   _mesa_sha1_compute(one_MB, 1024 * 1024, one_MB_key);
+   one_MB_key[0] = blob_key_byte_zero;;
+
+   cache_put(cache, one_MB_key, one_MB, 1024 * 1024);
+
+   free(one_MB);
+
+   count = 0;
+   if (does_cache_contain(cache, blob_key))
+       count++;
+
+   if (does_cache_contain(cache, string_key))
+       count++;
+
+   if (does_cache_contain(cache, one_KB_key))
+       count++;
+
+   expect_equal(count, 2, "eviction after overflow with MAX_SIZE=1M");
+
+   cache_destroy(cache);
+}
+
+static void
+test_put_key_and_get_key(void)
+{
+   struct program_cache *cache;
+   bool result;
+
+   uint8_t key_a[20] = {  0,  1,  2,  3,  4,  5,  6,  7,  8,  9,
+                         10, 11, 12, 13, 14, 15, 16, 17, 18, 19};
+   uint8_t key_b[20] = { 20, 21, 22, 23, 24, 25, 26, 27, 28, 29,
+                         30, 33, 32, 33, 34, 35, 36, 37, 38, 39};
+   uint8_t key_a_collide[20] =
+                        { 0,  1, 42, 43, 44, 45, 46, 47, 48, 49,
+                         50, 55, 52, 53, 54, 55, 56, 57, 58, 59};
+
+   cache = cache_create();
+
+   /* First test that cache_has_key returns false before cache_put_key */
+   result = cache_has_key(cache, key_a);
+   expect_equal(result, 0, "cache_has_key before key added");
+
+   /* Then a couple of tests of cache_put_key followed by cache_has_key */
+   cache_put_key(cache, key_a);
+   result = cache_has_key(cache, key_a);
+   expect_equal(result, 1, "cache_has_key after key added");
+
+   cache_put_key(cache, key_b);
+   result = cache_has_key(cache, key_b);
+   expect_equal(result, 1, "2nd cache_has_key after key added");
+
+   /* Test that a key with the same two bytes as an existing key
+    * forces an eviction.
+    */
+   cache_put_key(cache, key_a_collide);
+   result = cache_has_key(cache, key_a_collide);
+   expect_equal(result, 1, "put_key of a colliding key lands in the cache");
+
+   result = cache_has_key(cache, key_a);
+   expect_equal(result, 0, "put_key of a colliding key evicts from the cache");
+
+   /* And finally test that we can re-add the original key to re-evict
+    * the colliding key.
+    */
+   cache_put_key(cache, key_a);
+   result = cache_has_key(cache, key_a);
+   expect_equal(result, 1, "put_key of original key lands again");
+
+   result = cache_has_key(cache, key_a_collide);
+   expect_equal(result, 0, "put_key of orginal key evicts the colliding key");
+
+   cache_destroy(cache);
+}
+
+int
+main(void)
+{
+   int err;
+
+   test_cache_create();
+
+   test_put_and_get();
+
+   test_put_key_and_get_key();
+
+   err = rmrf_local(CACHE_TEST_TMP);
+   expect_equal(err, 0, "Removing " CACHE_TEST_TMP " again");
+
+   return error ? 1 : 0;
+}