Add new StringInfo APIs to allow callers to specify the buffer size.

Previously StringInfo APIs allocated buffers with fixed initial
allocation size of 1024 bytes. This may be too large and inappropriate
for some callers that can do with smaller memory buffers. To fix this,
introduce new APIs that allow callers to specify initial buffer size.

extern StringInfo makeStringInfoExt(int initsize);
extern void initStringInfoExt(StringInfo str, int initsize);

Existing APIs (makeStringInfo() and initStringInfo()) are changed to
call makeStringInfoExt and initStringInfoExt respectively (via inline
helper functions makeStringInfoInternal and initStringInfoInternal),
with the default buffer size of 1024.

Reviewed-by: Nathan Bossart, David Rowley, Michael Paquier, Gurjeet Singh
Discussion: https://postgr.es/m/20241225.123704.1194662271286702010.ishii%40postgresql.org

1 files changed, 61 insertions, 10 deletions

diff --git a/src/common/stringinfo.c b/src/common/stringinfo.c
index 55d2fbb864d..f4317003411 100644
--- a/src/common/stringinfo.c
+++ b/src/common/stringinfo.c
@@ -30,6 +30,40 @@
 
 
 /*
+ * initStringInfoInternal
+ *
+ * Initialize a StringInfoData struct (with previously undefined contents)
+ * to describe an empty string.
+ * The initial memory allocation size is specified by 'initsize'.
+ * The valid range for 'initsize' is 1 to MaxAllocSize.
+ */
+static inline void
+initStringInfoInternal(StringInfo str, int initsize)
+{
+	Assert(initsize >= 1 && initsize <= MaxAllocSize);
+
+	str->data = (char *) palloc(initsize);
+	str->maxlen = initsize;
+	resetStringInfo(str);
+}
+
+/*
+ * makeStringInfoInternal(int initsize)
+ *
+ * Create an empty 'StringInfoData' & return a pointer to it.
+ * The initial memory allocation size is specified by 'initsize'.
+ * The valid range for 'initsize' is 1 to MaxAllocSize.
+ */
+static inline StringInfo
+makeStringInfoInternal(int initsize)
+{
+	StringInfo	res = (StringInfo) palloc(sizeof(StringInfoData));
+
+	initStringInfoInternal(res, initsize);
+	return res;
+}
+
+/*
  * makeStringInfo
  *
  * Create an empty 'StringInfoData' & return a pointer to it.
@@ -37,13 +71,20 @@
 StringInfo
 makeStringInfo(void)
 {
-	StringInfo	res;
-
-	res = (StringInfo) palloc(sizeof(StringInfoData));
-
-	initStringInfo(res);
+	return makeStringInfoInternal(STRINGINFO_DEFAULT_SIZE);
+}
 
-	return res;
+/*
+ * makeStringInfoExt(int initsize)
+ *
+ * Create an empty 'StringInfoData' & return a pointer to it.
+ * The initial memory allocation size is specified by 'initsize'.
+ * The valid range for 'initsize' is 1 to MaxAllocSize.
+ */
+StringInfo
+makeStringInfoExt(int initsize)
+{
+	return makeStringInfoInternal(initsize);
 }
 
 /*
@@ -55,11 +96,21 @@ makeStringInfo(void)
 void
 initStringInfo(StringInfo str)
 {
-	int			size = 1024;	/* initial default buffer size */
+	return initStringInfoInternal(str, STRINGINFO_DEFAULT_SIZE);
+}
 
-	str->data = (char *) palloc(size);
-	str->maxlen = size;
-	resetStringInfo(str);
+/*
+ * initStringInfoExt
+ *
+ * Initialize a StringInfoData struct (with previously undefined contents)
+ * to describe an empty string.
+ * The initial memory allocation size is specified by 'initsize'.
+ * The valid range for 'initsize' is 1 to MaxAllocSize.
+ */
+void
+initStringInfoExt(StringInfo str, int initsize)
+{
+	initStringInfoInternal(str, initsize);
 }
 
 /*