Add optional mmap(3) allocator

src/mmap_allocator.c

@@ -0,0 +1,139 @@
+/* threadless.io
+ * Copyright (c) 2016 Justin R. Cutler
+ * Licensed under the MIT License. See LICENSE file in the project root for
+ * full license information.
+ */
+/** @file
+ * @c mmap(3) allocator implementation
+ * @author Justin R. Cutler <justin.r.cutler@gmail.com>
+ */
+
+#define _GNU_SOURCE
+
+/* HAVE_* */
+#include "config.h"
+
+/* errno, ENOSYS */
+#include <errno.h>
+/* size_t, NULL */
+#include <stddef.h>
+#ifndef HAVE_MREMAP
+/* memcpy */
+# include <string.h>
+#endif
+
+/* mmap, munmap, PROT_*, MAP_*, mremap(optional), MREMAP_*(optional) */
+#include <sys/mman.h>
+/* sysconf, _SC_PAGESIZE */
+#include <unistd.h>
+
+/* ... */
+#include <threadless/mmap_allocator.h>
+
+
+#ifndef HAVE_MMAP
+# error Need mmap()
+#endif
+
+#if defined(HAVE_MAP_ANONYMOUS) || defined(HAVE_MAP_ANON)
+# ifndef HAVE_MAP_ANONYMOUS
+#  define MAP_ANONYMOUS MAP_ANON
+# endif
+#else
+# error Need MAP_ANONYMOUS or MAP_ANON
+#endif
+
+
+static void *do_mmap(size_t size)
+{
+    return mmap(NULL, size, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
+        -1, 0);
+}
+
+
+static void *do_mremap(void *memory, size_t old_size, size_t new_size)
+{
+    void *new_memory;
+#ifdef HAVE_MREMAP
+    new_memory = mremap(memory, old_size, new_size, MREMAP_MAYMOVE);
+#else
+    /* slow remap: mmap + copy + munmap */
+    size_t copy_size = (new_size < old_size) ? new_size : old_size;
+    new_memory = do_mmap(new_size);
+    if (MAP_FAILED != new_memory) {
+        memcpy(new_memory, memory, copy_size);
+        (void) munmap(memory, old_size);
+    }
+#endif
+    return new_memory;
+}
+
+
+static int mmap_allocate(allocation_t *allocation, size_t size)
+{
+    static size_t page_size = 0;
+    static size_t page_mask = 0;
+    void *new_memory = MAP_FAILED;
+
+    if (!page_size) {
+        /* get page size */
+        long result = sysconf(_SC_PAGESIZE);
+        if (result > 0 && !(result & (result - 1))) {
+            page_size = (size_t) result;
+            page_mask = page_size - 1;
+        } else {
+            /* not a power of 2 */
+            errno = ENOSYS;
+            return -1;
+        }
+    }
+
+    /* round size up to multiple of page_size */
+    size = (size + page_size - 1) & ~page_mask;
+
+    /* no action required */
+    if (size == allocation->size) {
+        return 0;
+    }
+
+    if (0 == size) {
+        if (NULL != allocation->memory && 0 != allocation->size) {
+            (void)munmap(allocation->memory, allocation->size);
+        }
+        new_memory = NULL;
+    } else if (0 == allocation->size) {
+        new_memory = do_mmap(size);
+    } else {
+        new_memory = do_mremap(allocation->memory, allocation->size, size);
+    }
+
+    if (MAP_FAILED == new_memory) {
+        /* operation failed */
+        return -1;
+    }
+
+    /* update allocation */
+    allocation->memory = new_memory;
+    allocation->size = size;
+
+    return 0;
+}
+
+
+static void mmap_destroy(allocator_t *allocator)
+{
+    /* ignore allocator */
+    (void) allocator;
+}
+
+
+static allocator_t mmap_allocator = {
+    .allocate = mmap_allocate,
+    .destroy = mmap_destroy,
+};
+
+
+allocator_t *allocator_get_mmap(void)
+{
+    return &mmap_allocator;
+}