Add pool allocator

include/ucore/spool.h

@@ -0,0 +1,60 @@
+#ifndef UC_SPOOL_H_
+#define UC_SPOOL_H
+
+#include <stddef.h>
+#include <stdint.h>
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/** @file
+ * Static pool allocator.
+ *
+ *  An UCPool allocates fixed size memory chunks from a provided buffer,
+ *  and memory allocations can be free'd in any order.
+ *
+ * The backing array should be suitable aligned to the types
+ * that will be allocated from it. Use .e.g
+ * @code
+ * _Alignas(16) char mem[1024];
+ * @endcode
+ * as the backing buffer.
+ *
+*/
+typedef struct UCPool UCPool;
+struct UCPool {
+   unsigned char *free_list;   // intrusive free list
+   size_t block_size; // aligned size of each block
+   size_t capacity;   // number of blocks
+   size_t align;      // alignment
+   unsigned char *start;       // start of user buffer
+   unsigned char *end;         // one past end of user buffer
+};
+
+/** Initialize the pool.
+ *
+ * Block size will be rounded up by alignment, or to size of a pointer
+ *
+ * @param buffer      backing buffer for the pool
+ * @param buffer_size size of @buffer
+ * @param block_size  size of each allocation.
+ * @param alignment   alignment of each block (must be power of 2)
+ */
+void uc_pool_init(UCPool *pool,
+               void *buffer,
+               size_t buffer_size,
+               size_t block_size,
+               size_t alignment);
+
+// Allocate a block from the pool. Returns NULL if no more space
+void *uc_pool_alloc(UCPool *pool);
+
+// Free @p . Returns memory to the pool
+void uc_pool_free(UCPool *pool, void *p);
+void uc_pool_reset(UCPool *pool);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif

src/spool.c

@@ -0,0 +1,111 @@
+#include <assert.h>
+#include "ucore/spool.h"
+#include "ucore/utils.h"
+#include <string.h>
+
+void uc_pool_init(UCPool *pool, void *buffer, size_t buffer_size, size_t block_size, size_t align)
+{
+    assert(align > 0);
+    assert((align & (align - 1)) == 0); // power of 2
+
+
+    // enforce minimum for storing free list pointers
+
+    if (align < _Alignof(unsigned char *)) {
+        align = _Alignof(unsigned char *);
+    }
+
+    if (block_size < sizeof(unsigned char *)) {
+        block_size = sizeof(unsigned char *);
+    }
+    // ensure initial alignment
+    size_t stride = UC_ALIGN(block_size, align);
+
+    // align first usable block
+    uintptr_t start_addr = (uintptr_t)buffer;
+    uintptr_t first_addr = UC_ALIGN(start_addr, align);
+    size_t padding = first_addr - start_addr;
+
+    if (padding + stride > buffer_size) {
+        pool->capacity = 0;
+        pool->free_list = NULL;
+    } else {
+        size_t usable = buffer_size - padding;
+        pool->capacity = usable / stride;
+
+        // build intrusive free list
+        unsigned char *p = (unsigned char *)first_addr;
+        for (size_t i = 0; i < pool->capacity - 1; ++i) {
+            *(unsigned char **)p = p + stride;
+            p += stride;
+        }
+        *(unsigned char **)p = NULL; // last element
+        pool->free_list = (unsigned char *)first_addr;
+    }
+
+    pool->block_size = stride;
+    pool->align      = align;
+    pool->start      = (unsigned char *)buffer;
+    pool->end        = (unsigned char *)buffer + buffer_size;
+}
+
+
+void *uc_pool_alloc(UCPool *pool)
+{
+    if (!pool->free_list) {
+        return NULL;
+    }
+    unsigned char *block = pool->free_list;
+    pool->free_list = *(unsigned char **)block;
+
+#ifdef DEBUG
+    memset(block, 0xCB, pool->block_size);
+#endif
+    return block;
+}
+#include <stdio.h>
+
+void uc_pool_free(UCPool *pool, void *p)
+{
+    if (p == NULL) {
+        return;
+    }
+#ifdef DEBUG
+    assert((unsigned char *)p >= pool->start && (unsigned char*)p < pool->end);
+    assert(((uintptr_t)p - (uintptr_t)pool->start) % pool->block_size == 0);
+
+    // double-free detection
+    for (unsigned char *f = pool->free_list; f; f = *(unsigned char**)f) {
+        if (f == p) {
+            assert(0 && "Double free detected in pool!");
+            return;
+        }
+    }
+
+    memset(p, 0xDD, pool->block_size);
+#endif
+     // When not in use, store pointer to next free element inline in the block
+    *(unsigned char **)p = pool->free_list;
+    pool->free_list = p;
+}
+
+
+void uc_pool_reset(UCPool *pool)
+{
+   if (pool->capacity == 0)
+        return;
+
+    uintptr_t start_addr = (uintptr_t)pool->start;
+    uintptr_t first_addr = UC_ALIGN(start_addr, pool->align);
+
+    unsigned char *p = (unsigned char *)first_addr;
+    // build intrusive free list
+    for (size_t i = 0; i < pool->capacity - 1; ++i) {
+        *(unsigned char **)p = p + pool->block_size;
+        p += pool->block_size;
+    }
+
+    *(unsigned char **)p = NULL;  // last element
+
+    pool->free_list = (unsigned char *)first_addr;
+}