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Use buffers when constructing string node lists.

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Hi Veillard and all,

Firstly, thanks for libxml: it's awesome!

I noticed recently that libxml was taking a surprisingly long time to perform some
operations (many minutes instead of milliseconds), and so I did some digging. It turns out
that the problem was caused by the realloc()ing done in xmlNodeAddContentLen() which can
be called many (many) times when assigning some content into a node.

For background, I'm dealing with XML that contains emails, these can have large
attachments (~6MB) which are base-64 encoded, line-wrapped at 78 chars, and each line ends
with 
. This means that xmlNodeAddContentLen() is being called about 200,000 times,
and so there are 200,000 reallocs of a 6MB string, which takes a while... (I put a synthetic
example of this at https://gist.github.com/2656940)

The attached patch works around that problem by using the existing buffer API to merge the
strings together before even creating the text node, this keeps the number of realloc()s
at a managable level.

I'd love feedback on the patch, and am happy to fix problems with it, or explore other
solutions if you think that this is barking up the wrong tree :).

Thanks,

Conrad

P.S. Should I create a bug for this too?

------8<------

Before this change xmlStringGetNodeList would perform a realloc() of the
entire new content for every XML entity in the assigned text in order to
merge together adjacent text nodes. This had the effect of making
xmlSetNodeContent O(n^2), which led to unexpectedly bad performance on
inputs that contained a large number of XML entities.

After this change the memory management is done by the buffer API,
avoiding the need to continually re-measure and realloc() the string.

For my test data (6MB of 80 character lines, each ending with &#13;)
this takes the time to xmlSetNodeContent from about 500 seconds to
around 50ms. I have not profiled smaller cases, though I tried to
minimize the performance impact of my change by avoiding unnecessary
string copying.

Signed-off-by: Conrad Irwin <conrad.irwin@gmail.com>
This commit is contained in:
Conrad Irwin 2012-05-10 20:17:25 -07:00 committed by Daniel Veillard
parent a0cd075d94
commit 7d553f834e
2 changed files with 119 additions and 83 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/libxml/tree.h
View File

@ -694,6 +694,8 @@ XMLPUBFUN void XMLCALL
xmlBufferEmpty (xmlBufferPtr buf);
XMLPUBFUN const xmlChar* XMLCALL
xmlBufferContent (const xmlBufferPtr buf);
XMLPUBFUN xmlChar* XMLCALL
xmlBufferDetach (const xmlBufferPtr buf);
XMLPUBFUN void XMLCALL
xmlBufferSetAllocationScheme(xmlBufferPtr buf,
xmlBufferAllocationScheme scheme);

200
tree.c
View File

@ -1261,9 +1261,13 @@ xmlStringLenGetNodeList(xmlDocPtr doc, const xmlChar *value, int len) {
const xmlChar *cur = value, *end = cur + len;
const xmlChar *q;
xmlEntityPtr ent;
xmlBufferPtr buffer;
if (value == NULL) return(NULL);
buffer = xmlBufferCreateSize(0);
if (buffer == NULL) return(NULL);
q = cur;
while ((cur < end) && (*cur != 0)) {
if (cur[0] == '&') {
@ -1274,19 +1278,8 @@ xmlStringLenGetNodeList(xmlDocPtr doc, const xmlChar *value, int len) {
* Save the current text.
*/
if (cur != q) {
if ((last != NULL) && (last->type == XML_TEXT_NODE)) {
xmlNodeAddContentLen(last, q, cur - q);
} else {
node = xmlNewDocTextLen(doc, q, cur - q);
if (node == NULL) return(ret);
if (last == NULL)
last = ret = node;
else {
last->next = node;
node->prev = last;
last = node;
}
}
if (xmlBufferAdd(buffer, q, cur - q))
goto out;
}
q = cur;
if ((cur + 2 < end) && (cur[1] == '#') && (cur[2] == 'x')) {
@ -1351,7 +1344,7 @@ xmlStringLenGetNodeList(xmlDocPtr doc, const xmlChar *value, int len) {
if ((cur >= end) || (*cur == 0)) {
xmlTreeErr(XML_TREE_UNTERMINATED_ENTITY, (xmlNodePtr) doc,
(const char *) q);
return(ret);
goto out;
}
if (cur != q) {
/*
@ -1361,23 +1354,36 @@ xmlStringLenGetNodeList(xmlDocPtr doc, const xmlChar *value, int len) {
ent = xmlGetDocEntity(doc, val);
if ((ent != NULL) &&
(ent->etype == XML_INTERNAL_PREDEFINED_ENTITY)) {
if (last == NULL) {
node = xmlNewDocText(doc, ent->content);
last = ret = node;
} else if (last->type != XML_TEXT_NODE) {
node = xmlNewDocText(doc, ent->content);
last = xmlAddNextSibling(last, node);
} else
xmlNodeAddContent(last, ent->content);
if (xmlBufferCat(buffer, ent->content))
goto out;
} else {
/*
* Flush buffer so far
*/
if (buffer->use) {
node = xmlNewDocText(doc, NULL);
if (node == NULL) {
if (val != NULL) xmlFree(val);
goto out;
}
node->content = xmlBufferDetach(buffer);
if (last == NULL) {
last = ret = node;
} else {
last = xmlAddNextSibling(last, node);
}
}
/*
* Create a new REFERENCE_REF node
*/
node = xmlNewReference(doc, val);
if (node == NULL) {
if (val != NULL) xmlFree(val);
return(ret);
goto out;
}
else if ((ent != NULL) && (ent->children == NULL)) {
xmlNodePtr temp;
@ -1409,35 +1415,39 @@ xmlStringLenGetNodeList(xmlDocPtr doc, const xmlChar *value, int len) {
l = xmlCopyCharMultiByte(buf, charval);
buf[l] = 0;
node = xmlNewDocText(doc, buf);
if (node != NULL) {
if (last == NULL) {
last = ret = node;
} else {
last = xmlAddNextSibling(last, node);
}
}
if (xmlBufferCat(buffer, buf))
goto out;
charval = 0;
}
} else
cur++;
}
if ((cur != q) || (ret == NULL)) {
if (cur != q) {
/*
* Handle the last piece of text.
*/
if ((last != NULL) && (last->type == XML_TEXT_NODE)) {
xmlNodeAddContentLen(last, q, cur - q);
} else {
node = xmlNewDocTextLen(doc, q, cur - q);
if (node == NULL) return(ret);
if (last == NULL) {
ret = node;
} else {
xmlAddNextSibling(last, node);
}
}
if (xmlBufferAdd(buffer, q, cur - q))
goto out;
}
if (buffer->use) {
node = xmlNewDocText(doc, NULL);
if (node == NULL) goto out;
node->content = xmlBufferDetach(buffer);
if (last == NULL) {
last = ret = node;
} else {
last = xmlAddNextSibling(last, node);
}
} else if (ret == NULL) {
ret = xmlNewDocText(doc, BAD_CAST "");
}
out:
xmlBufferFree(buffer);
return(ret);
}
@ -1458,9 +1468,13 @@ xmlStringGetNodeList(xmlDocPtr doc, const xmlChar *value) {
const xmlChar *cur = value;
const xmlChar *q;
xmlEntityPtr ent;
xmlBufferPtr buffer;
if (value == NULL) return(NULL);
buffer = xmlBufferCreateSize(0);
if (buffer == NULL) return(NULL);
q = cur;
while (*cur != 0) {
if (cur[0] == '&') {
@ -1471,19 +1485,8 @@ xmlStringGetNodeList(xmlDocPtr doc, const xmlChar *value) {
* Save the current text.
*/
if (cur != q) {
if ((last != NULL) && (last->type == XML_TEXT_NODE)) {
xmlNodeAddContentLen(last, q, cur - q);
} else {
node = xmlNewDocTextLen(doc, q, cur - q);
if (node == NULL) return(ret);
if (last == NULL)
last = ret = node;
else {
last->next = node;
node->prev = last;
last = node;
}
}
if (xmlBufferAdd(buffer, q, cur - q))
goto out;
}
q = cur;
if ((cur[1] == '#') && (cur[2] == 'x')) {
@ -1536,7 +1539,7 @@ xmlStringGetNodeList(xmlDocPtr doc, const xmlChar *value) {
if (*cur == 0) {
xmlTreeErr(XML_TREE_UNTERMINATED_ENTITY,
(xmlNodePtr) doc, (const char *) q);
return(ret);
goto out;
}
if (cur != q) {
/*
@ -1546,23 +1549,32 @@ xmlStringGetNodeList(xmlDocPtr doc, const xmlChar *value) {
ent = xmlGetDocEntity(doc, val);
if ((ent != NULL) &&
(ent->etype == XML_INTERNAL_PREDEFINED_ENTITY)) {
if (last == NULL) {
node = xmlNewDocText(doc, ent->content);
last = ret = node;
} else if (last->type != XML_TEXT_NODE) {
node = xmlNewDocText(doc, ent->content);
last = xmlAddNextSibling(last, node);
} else
xmlNodeAddContent(last, ent->content);
if (xmlBufferCat(buffer, ent->content))
goto out;
} else {
/*
* Flush buffer so far
*/
if (buffer->use) {
node = xmlNewDocText(doc, NULL);
node->content = xmlBufferDetach(buffer);
if (last == NULL) {
last = ret = node;
} else {
last = xmlAddNextSibling(last, node);
}
}
/*
* Create a new REFERENCE_REF node
*/
node = xmlNewReference(doc, val);
if (node == NULL) {
if (val != NULL) xmlFree(val);
return(ret);
goto out;
}
else if ((ent != NULL) && (ent->children == NULL)) {
xmlNodePtr temp;
@ -1593,14 +1605,10 @@ xmlStringGetNodeList(xmlDocPtr doc, const xmlChar *value) {
len = xmlCopyCharMultiByte(buf, charval);
buf[len] = 0;
node = xmlNewDocText(doc, buf);
if (node != NULL) {
if (last == NULL) {
last = ret = node;
} else {
last = xmlAddNextSibling(last, node);
}
}
if (xmlBufferCat(buffer, buf))
goto out;
charval = 0;
}
} else
cur++;
@ -1609,18 +1617,22 @@ xmlStringGetNodeList(xmlDocPtr doc, const xmlChar *value) {
/*
* Handle the last piece of text.
*/
if ((last != NULL) && (last->type == XML_TEXT_NODE)) {
xmlNodeAddContentLen(last, q, cur - q);
xmlBufferAdd(buffer, q, cur - q);
}
if (buffer->use) {
node = xmlNewDocText(doc, NULL);
node->content = xmlBufferDetach(buffer);
if (last == NULL) {
last = ret = node;
} else {
node = xmlNewDocTextLen(doc, q, cur - q);
if (node == NULL) return(ret);
if (last == NULL) {
last = ret = node;
} else {
last = xmlAddNextSibling(last, node);
}
last = xmlAddNextSibling(last, node);
}
}
out:
xmlBufferFree(buffer);
return(ret);
}
@ -6915,6 +6927,28 @@ xmlBufferCreateSize(size_t size) {
return(ret);
}
/**
* xmlBufferDetach
* @buf: the buffer
*
* Returns the previous string contained by the buffer.
*
*/
xmlChar *
xmlBufferDetach(xmlBufferPtr buf) {
xmlChar *ret;
if (buf == NULL) return(NULL);
ret = buf->content;
buf->content = NULL;
buf->size = 0;
buf->use = 0;
return ret;
}
/**
* xmlBufferCreateStatic:
* @mem: the memory area