[PATCH 1/6] Add memory pool library

[Ramkumar Ramachandra <artagnon@gmail.com>]

Add a memory pool library implemented using cpp macros. The library
provides macros that can be used to create a type-specific memory pool
API.

Signed-off-by: David Barr <david.barr@cordelta.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
---
 vcs-svn/obj_pool.h |   98 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 98 insertions(+), 0 deletions(-)
 create mode 100644 vcs-svn/obj_pool.h

diff --git a/vcs-svn/obj_pool.h b/vcs-svn/obj_pool.h
new file mode 100644
index 0000000..84c8321
--- /dev/null
+++ b/vcs-svn/obj_pool.h
@@ -0,1 +1,98 @@
+#ifndef OBJ_POOL_H_
+#define OBJ_POOL_H_
+
+#include "git-compat-util.h"
+
+/*
+ * The obj_pool_gen() macro generates a type-specific memory pool
+ * implementation.
+ *
+ * Arguments:
+ *
+ *   pre              : Prefix for generated functions (ex: string_).
+ *   obj_t            : Type for treap data structure (ex: char).
+ *   intial_capacity  : The initial size of the memory pool (ex: 4096).
+ *
+ */
+#define obj_pool_gen(pre, obj_t, initial_capacity) \
+static struct { \
+	uint32_t size; \
+	uint32_t capacity; \
+	obj_t *base; \
+	FILE *file; \
+} pre##_pool = { 0, 0, NULL, NULL}; \
+static void pre##_init(void) \
+{ \
+	struct stat st; \
+	size_t ps = sysconf (_SC_PAGESIZE); \
+	/* Touch binary file before opening read/write */ \
+	pre##_pool.file = fopen(#pre ".bin", "a"); \
+	fclose(pre##_pool.file); \
+	/* Open, check size, compute capacity */ \
+	pre##_pool.file = fopen(#pre ".bin", "r+"); \
+	fstat(fileno(pre##_pool.file), &st); \
+	pre##_pool.size = st.st_size / sizeof(obj_t); \
+	pre##_pool.capacity = ((st.st_size + ps - 1) & ~(ps - 1)) / sizeof(obj_t); \
+	if (pre##_pool.capacity < initial_capacity) \
+		pre##_pool.capacity = initial_capacity; \
+	/* Truncate to calculated capacity and map to VM */ \
+	ftruncate(fileno(pre##_pool.file), pre##_pool.capacity * sizeof(obj_t)); \
+	pre##_pool.base = mmap(0, pre##_pool.capacity * sizeof(obj_t), \
+				PROT_READ | PROT_WRITE, MAP_SHARED, \
+				fileno(pre##_pool.file), 0); \
+} \
+static uint32_t pre##_alloc(uint32_t count) \
+{ \
+	uint32_t offset; \
+	if (pre##_pool.size + count > pre##_pool.capacity) { \
+		if (NULL == pre##_pool.base) \
+			pre##_init(); \
+		fsync(fileno(pre##_pool.file)); \
+		munmap(pre##_pool.base, \
+			pre##_pool.capacity * sizeof(obj_t)); \
+		pre##_pool.base = NULL; \
+		while (pre##_pool.size + count > pre##_pool.capacity) \
+			if (pre##_pool.capacity) \
+				pre##_pool.capacity *= 2; \
+			else \
+				pre##_pool.capacity = initial_capacity; \
+		ftruncate(fileno(pre##_pool.file), \
+				pre##_pool.capacity * sizeof(obj_t)); \
+		pre##_pool.base = \
+			mmap(0, pre##_pool.capacity * sizeof(obj_t), \
+				PROT_READ | PROT_WRITE, MAP_SHARED, \
+				fileno(pre##_pool.file), 0); \
+	} \
+	offset = pre##_pool.size; \
+	pre##_pool.size += count; \
+	return offset; \
+} \
+static void pre##_free(uint32_t count) \
+{ \
+	pre##_pool.size -= count; \
+} \
+static uint32_t pre##_offset(obj_t *obj) \
+{ \
+	return obj == NULL ? ~0 : obj - pre##_pool.base; \
+} \
+static obj_t *pre##_pointer(uint32_t offset) \
+{ \
+	return offset >= pre##_pool.size ? NULL : &pre##_pool.base[offset]; \
+} \
+static void pre##_reset(void) \
+{ \
+	if (pre##_pool.base) { \
+		fsync(fileno(pre##_pool.file)); \
+		munmap(pre##_pool.base, \
+			pre##_pool.capacity * sizeof(obj_t)); \
+		ftruncate(fileno(pre##_pool.file), \
+				pre##_pool.size * sizeof(obj_t)); \
+		fclose(pre##_pool.file); \
+	} \
+	pre##_pool.base = NULL; \
+	pre##_pool.size = 0; \
+	pre##_pool.capacity = 0; \
+	pre##_pool.file = NULL; \
+}
+
+#endif
-- 
1.7.1