From: Sebastian Harl <sh@tokkee.org>
Date: Wed, 17 Sep 2014 09:10:13 +0000 (+0200)
Subject: utils strbuf: Added 'min_size' to be considered when shrinking the buffer.
X-Git-Tag: sysdb-0.5.0~32
X-Git-Url: https://git.tokkee.org/?a=commitdiff_plain;h=3cd97771183ee38e5fc8c3b2268cffce3c2cb27c;p=sysdb.git

utils strbuf: Added 'min_size' to be considered when shrinking the buffer.

It's set to the initial size of the buffer (or 64). The idea is that the
initial size should provide an estimate of a reasonable size and shrinking the
buffer below that size causes unecessary churn.

For example, this is important for the frontend's command handlers which
usually need a large buffer size but initial writes to the buffer may be
small.
---

diff --git a/src/utils/strbuf.c b/src/utils/strbuf.c
index c310b44..ecc0531 100644
--- a/src/utils/strbuf.c
+++ b/src/utils/strbuf.c
@@ -39,7 +39,8 @@
 /* free memory if most of the buffer is unused */
 #define CHECK_SHRINK(buf) \
 	do { \
-		if ((buf)->pos < (buf)->size / 3) \
+		if (((buf)->pos < (buf)->size / 3) \
+				&& (2 * (buf)->pos > (buf)->min_size)) \
 			/* don't free all memory to avoid churn */ \
 			strbuf_resize((buf), 2 * (buf)->pos); \
 	} while (0)
@@ -52,6 +53,9 @@ struct sdb_strbuf {
 	char  *string;
 	size_t size;
 	size_t pos;
+
+	/* min size to shrink the buffer to */
+	size_t min_size;
 };
 
 /*
@@ -100,7 +104,10 @@ sdb_strbuf_create(size_t size)
 		}
 
 		buf->string[0] = '\0';
+		buf->min_size = size;
 	}
+	else
+		buf->min_size = 64;
 
 	buf->size = size;
 	buf->pos  = 0;
diff --git a/t/unit/utils/strbuf_test.c b/t/unit/utils/strbuf_test.c
index e7cb9f5..cb86a3e 100644
--- a/t/unit/utils/strbuf_test.c
+++ b/t/unit/utils/strbuf_test.c
@@ -233,6 +233,9 @@ START_TEST(test_sprintf)
 
 	size_t i;
 
+	sdb_strbuf_destroy(buf);
+	buf = sdb_strbuf_create(1); /* -> min_size = 1 */
+
 	for (i = 0; i < SDB_STATIC_ARRAY_LEN(golden_data); ++i) {
 		n = sdb_strbuf_sprintf(buf, "%s", golden_data[i]);
 		fail_unless((size_t)n == strlen(golden_data[i]),
@@ -251,7 +254,9 @@ START_TEST(test_sprintf)
 				"got: %s; expected: %s", test, golden_data[i]);
 
 		check = sdb_strbuf_cap(buf);
-		if (n) /* 3 times the current len is the threshold for shrinking */
+		/* 3 times the current len is the threshold for shrinking,
+		 * but it's capped to the initial size (or 64) */
+		if (n)
 			fail_unless(((size_t)n < check) && (check < (size_t)n * 3),
 					"sdb_strbuf_sprintf() did not resize the buffer "
 					"correctly (got size %zu; expected %zi < <size> < %d)",