Add memory pool library

Add a memory pool library implemented using C macros. The
obj_pool_gen() macro creates a type-specific memory pool.

The memory pool library is distinguished from the existing specialized
allocators in alloc.c by using a contiguous block for all allocations.
This means that on one hand, long-lived pointers have to be written as
offsets, since the base address changes as the pool grows, but on the
other hand, the entire pool can be easily written to the file system.
This could allow the memory pool to persist between runs of an
application.

For the svn importer, such a facility is useful because each svn
revision can copy trees and files from any previous revision.  The
relevant information for all revisions has to persist somehow to
support incremental runs.

[rr: minor cleanups]
[jn: added tests; removed file system backing for now]

Signed-off-by: David Barr <david.barr@cordelta.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 116 insertions, 0 deletions

diff --git a/test-obj-pool.c b/test-obj-pool.c
new file mode 100644
index 0000000000..5018863ef5
--- /dev/null
+++ b/test-obj-pool.c
@@ -0,0 +1,116 @@
+/*
+ * test-obj-pool.c: code to exercise the svn importer's object pool
+ */
+
+#include "cache.h"
+#include "vcs-svn/obj_pool.h"
+
+enum pool { POOL_ONE, POOL_TWO };
+obj_pool_gen(one, int, 1)
+obj_pool_gen(two, int, 4096)
+
+static uint32_t strtouint32(const char *s)
+{
+	char *end;
+	uintmax_t n = strtoumax(s, &end, 10);
+	if (*s == '\0' || (*end != '\n' && *end != '\0'))
+		die("invalid offset: %s", s);
+	return (uint32_t) n;
+}
+
+static void handle_command(const char *command, enum pool pool, const char *arg)
+{
+	switch (*command) {
+	case 'a':
+		if (!prefixcmp(command, "alloc ")) {
+			uint32_t n = strtouint32(arg);
+			printf("%"PRIu32"\n",
+				pool == POOL_ONE ?
+				one_alloc(n) : two_alloc(n));
+			return;
+		}
+	case 'c':
+		if (!prefixcmp(command, "commit ")) {
+			pool == POOL_ONE ? one_commit() : two_commit();
+			return;
+		}
+		if (!prefixcmp(command, "committed ")) {
+			printf("%"PRIu32"\n",
+				pool == POOL_ONE ?
+				one_pool.committed : two_pool.committed);
+			return;
+		}
+	case 'f':
+		if (!prefixcmp(command, "free ")) {
+			uint32_t n = strtouint32(arg);
+			pool == POOL_ONE ? one_free(n) : two_free(n);
+			return;
+		}
+	case 'n':
+		if (!prefixcmp(command, "null ")) {
+			printf("%"PRIu32"\n",
+				pool == POOL_ONE ?
+				one_offset(NULL) : two_offset(NULL));
+			return;
+		}
+	case 'o':
+		if (!prefixcmp(command, "offset ")) {
+			uint32_t n = strtouint32(arg);
+			printf("%"PRIu32"\n",
+				pool == POOL_ONE ?
+				one_offset(one_pointer(n)) :
+				two_offset(two_pointer(n)));
+			return;
+		}
+	case 'r':
+		if (!prefixcmp(command, "reset ")) {
+			pool == POOL_ONE ? one_reset() : two_reset();
+			return;
+		}
+	case 's':
+		if (!prefixcmp(command, "set ")) {
+			uint32_t n = strtouint32(arg);
+			if (pool == POOL_ONE)
+				*one_pointer(n) = 1;
+			else
+				*two_pointer(n) = 1;
+			return;
+		}
+	case 't':
+		if (!prefixcmp(command, "test ")) {
+			uint32_t n = strtouint32(arg);
+			printf("%d\n", pool == POOL_ONE ?
+				*one_pointer(n) : *two_pointer(n));
+			return;
+		}
+	default:
+		die("unrecognized command: %s", command);
+	}
+}
+
+static void handle_line(const char *line)
+{
+	const char *arg = strchr(line, ' ');
+	enum pool pool;
+
+	if (arg && !prefixcmp(arg + 1, "one"))
+		pool = POOL_ONE;
+	else if (arg && !prefixcmp(arg + 1, "two"))
+		pool = POOL_TWO;
+	else
+		die("no pool specified: %s", line);
+
+	handle_command(line, pool, arg + strlen("one "));
+}
+
+int main(int argc, char *argv[])
+{
+	struct strbuf sb = STRBUF_INIT;
+	if (argc != 1)
+		usage("test-obj-str < script");
+
+	while (strbuf_getline(&sb, stdin, '\n') != EOF)
+		handle_line(sb.buf);
+	strbuf_release(&sb);
+	return 0;
+}