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Refactor JSON_parser to use a single stack
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Summary: Reduces allocations to at most one per request, instead of 3.

Reviewed By: markw65

Differential Revision: D2585287

fb-gh-sync-id: 85f2b923513ec22e8fa679dedbaea3bfc7a89ad4
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@edwinsmith @hhvm-bot
edwinsmith authored and hhvm-bot committed Jan 4, 2016
1 parent 5d0692c commit 14c2397
Showing 1 changed file with 74 additions and 94 deletions.
168 changes: 74 additions & 94 deletions hphp/runtime/ext/json/JSON_parser.cpp
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Expand Up @@ -52,17 +52,6 @@ static const char long_min_digits[] = "9223372036854775808";

namespace HPHP {

#ifdef true
# undef true
#endif

#ifdef false
# undef false
#endif

#define true 1
#define false 0

/*
Characters are mapped into these 32 symbol classes. This allows for
significant reductions in the size of the state transition table.
Expand Down Expand Up @@ -221,7 +210,7 @@ alignas(64) static const int8_t loose_ascii_class[128] = {
The state transition table takes the current state and the current symbol,
and returns either a new state or an action. A new state is a number between
0 and 29. An action is a negative number between -1 and -9. A JSON text is
accepted if the end of the text is in state 9 and mode is MODE_DONE.
accepted if the end of the text is in state 9 and mode is Mode::DONE.
*/
alignas(64) static const int8_t state_transition_table[30][32] = {
/* 0*/ { 0, 0,-8,-1,-6,-1,-1,-1, 3,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1},
Expand Down Expand Up @@ -295,25 +284,36 @@ alignas(64) static const int8_t loose_state_transition_table[31][32] = {
};
/*</fb>*/

/**
* These modes can be pushed on the PDA stack.
*/
enum class Mode {
INVALID = 0,
DONE = 1,
KEY = 2,
OBJECT = 3,
ARRAY = 4
};

#define JSON_PARSER_DEFAULT_DEPTH 512
namespace {

/**
* A stack maintains the states of nested structures.
*/
struct json_parser {
std::vector<int> stack;
std::vector<Variant> zstack;
std::vector<String> kstack;
struct json_state {
Mode mode;
String key;
Variant val;
};
std::vector<json_state> stack;
int top;
int mark; // the watermark
int depth;
json_error_codes error_code;
json_parser() : stack(JSON_PARSER_DEFAULT_DEPTH),
zstack(JSON_PARSER_DEFAULT_DEPTH),
kstack(JSON_PARSER_DEFAULT_DEPTH) {};
};

}

IMPLEMENT_THREAD_LOCAL(json_parser, s_json_parser);

Expand All @@ -324,6 +324,7 @@ IMPLEMENT_THREAD_LOCAL(json_parser, s_json_parser);
json_error_codes json_get_last_error_code() {
return s_json_parser->error_code;
}

void json_set_last_error_code(json_error_codes ec) {
s_json_parser->error_code = ec;
}
Expand Down Expand Up @@ -360,36 +361,15 @@ static InitFiniNode init(
InitFiniNode::When::RequestInit
);

class JsonParserCleaner {
public:
explicit JsonParserCleaner(json_parser *json) : m_json(json) {}
~JsonParserCleaner() {
for (int i = 0; i <= m_json->mark; i++) {
m_json->zstack[i].unset();
m_json->kstack[i].reset();
}
}
private:
json_parser *m_json;
};

/**
* These modes can be pushed on the PDA stack.
*/
#define MODE_DONE 1
#define MODE_KEY 2
#define MODE_OBJECT 3
#define MODE_ARRAY 4

/**
* Push a mode onto the stack. Return false if there is overflow.
*/
static int push(json_parser *json, int mode) {
static int push(json_parser *json, Mode mode) {
if (json->top + 1 >= json->depth) {
return false;
}
json->top += 1;
json->stack[json->top] = mode;
json->stack[json->top].mode = mode;
if (json->top > json->mark) {
json->mark = json->top;
}
Expand All @@ -401,11 +381,11 @@ static int push(json_parser *json, int mode) {
* Pop the stack, assuring that the current mode matches the expectation.
* Return false if there is underflow or if the modes mismatch.
*/
static int pop(json_parser *json, int mode) {
if (json->top < 0 || json->stack[json->top] != mode) {
static int pop(json_parser *json, Mode mode) {
if (json->top < 0 || json->stack[json->top].mode != mode) {
return false;
}
json->stack[json->top] = 0;
json->stack[json->top].mode = Mode::INVALID;
json->top -= 1;
return true;
}
Expand Down Expand Up @@ -570,17 +550,17 @@ static void attach_zval(json_parser *json,
return;
}

Variant &root = json->zstack[json->top - 1];
Variant &child = json->zstack[json->top];
int up_mode = json->stack[json->top - 1];
auto& root = json->stack[json->top - 1].val;
auto& child = json->stack[json->top].val;
auto up_mode = json->stack[json->top - 1].mode;

if (up_mode == MODE_ARRAY) {
if (up_mode == Mode::ARRAY) {
if (collections) {
collections::append(root.getObjectData(), child.asCell());
} else {
root.toArrRef().append(child);
}
} else if (up_mode == MODE_OBJECT) {
} else if (up_mode == Mode::OBJECT) {
object_set(root, key, child, assoc, collections);
}
}
Expand All @@ -598,7 +578,6 @@ bool JSON_parser(Variant &z, const char *p, int length, bool const assoc,
int c; /* the next character class */
int s; /* the next state */
json_parser *json = s_json_parser.get(); /* the parser state */
JsonParserCleaner cleaner(json);
int state = 0;

/*<fb>*/
Expand Down Expand Up @@ -632,12 +611,16 @@ bool JSON_parser(Variant &z, const char *p, int length, bool const assoc,
// contracting. Calls with a depth other than default should be rare.
if (depth > json->stack.size()) {
json->stack.resize(depth);
json->zstack.resize(depth);
json->kstack.resize(depth);
}
SCOPE_EXIT {
for (int i = 0; i <= json->mark; i++) {
json->stack[i].key.reset();
json->stack[i].val.unset();
}
};

json->mark = json->top = -1;
push(json, MODE_DONE);
push(json, Mode::DONE);

UTF8To16Decoder decoder(p, length, loose);
for (;;) {
Expand Down Expand Up @@ -685,10 +668,8 @@ bool JSON_parser(Variant &z, const char *p, int length, bool const assoc,
empty }
*/
case -9:
attach_zval(json, json->kstack[json->top], assoc,
collections);

if (!pop(json, MODE_KEY)) {
attach_zval(json, json->stack[json->top].key, assoc, collections);
if (!pop(json, Mode::KEY)) {
return false;
}
state = 9;
Expand All @@ -697,14 +678,14 @@ bool JSON_parser(Variant &z, const char *p, int length, bool const assoc,
{
*/
case -8:
if (!push(json, MODE_KEY)) {
if (!push(json, Mode::KEY)) {
s_json_parser->error_code = JSON_ERROR_DEPTH;
return false;
}

state = 1;
if (json->top > 0) {
Variant &top = json->zstack[json->top];
Variant &top = json->stack[json->top].val;
if (json->top == 1) {
top.assignRef(z);
} else {
Expand All @@ -724,7 +705,7 @@ bool JSON_parser(Variant &z, const char *p, int length, bool const assoc,
/*<fb>*/
}
/*</fb>*/
json->kstack[json->top] = copy_and_clear(*key);
json->stack[json->top].key = copy_and_clear(*key);
reset_type();
}
break;
Expand All @@ -735,31 +716,31 @@ bool JSON_parser(Variant &z, const char *p, int length, bool const assoc,
/*** BEGIN Facebook: json_utf8_loose ***/
/*
If this is a trailing comma in an object definition,
we're in MODE_KEY. In that case, throw that off the
stack and restore MODE_OBJECT so that we pretend the
we're in Mode::KEY. In that case, throw that off the
stack and restore Mode::OBJECT so that we pretend the
trailing comma just didn't happen.
*/
if (loose) {
if (pop(json, MODE_KEY)) {
push(json, MODE_OBJECT);
if (pop(json, Mode::KEY)) {
push(json, Mode::OBJECT);
}
}
/*** END Facebook: json_utf8_loose ***/

if (type != -1 &&
json->stack[json->top] == MODE_OBJECT) {
json->stack[json->top].mode == Mode::OBJECT) {
Variant mval;
json_create_zval(mval, *buf, type, options);
Variant &top = json->zstack[json->top];
Variant &top = json->stack[json->top].val;
object_set(top, copy_and_clear(*key), mval, assoc, collections);
buf->clear();
reset_type();
}

attach_zval(json, json->kstack[json->top],
attach_zval(json, json->stack[json->top].key,
assoc, collections);

if (!pop(json, MODE_OBJECT)) {
if (!pop(json, Mode::OBJECT)) {
s_json_parser->error_code = JSON_ERROR_STATE_MISMATCH;
return false;
}
Expand All @@ -769,14 +750,14 @@ bool JSON_parser(Variant &z, const char *p, int length, bool const assoc,
[
*/
case -6:
if (!push(json, MODE_ARRAY)) {
if (!push(json, Mode::ARRAY)) {
s_json_parser->error_code = JSON_ERROR_DEPTH;
return false;
}
state = 2;

if (json->top > 0) {
Variant &top = json->zstack[json->top];
Variant &top = json->stack[json->top].val;
if (json->top == 1) {
top.assignRef(z);
} else {
Expand All @@ -789,7 +770,7 @@ bool JSON_parser(Variant &z, const char *p, int length, bool const assoc,
top = Array::Create();
}
/*</fb>*/
json->kstack[json->top] = copy_and_clear(*key);
json->stack[json->top].key = copy_and_clear(*key);
reset_type();
}
break;
Expand All @@ -799,10 +780,10 @@ bool JSON_parser(Variant &z, const char *p, int length, bool const assoc,
case -5:
{
if (type != -1 &&
json->stack[json->top] == MODE_ARRAY) {
json->stack[json->top].mode == Mode::ARRAY) {
Variant mval;
json_create_zval(mval, *buf, type, options);
auto& top = json->zstack[json->top];
auto& top = json->stack[json->top].val;
if (collections) {
collections::append(top.getObjectData(), mval.asCell());
} else {
Expand All @@ -812,10 +793,9 @@ bool JSON_parser(Variant &z, const char *p, int length, bool const assoc,
reset_type();
}

attach_zval(json, json->kstack[json->top],
assoc, collections);
attach_zval(json, json->stack[json->top].key, assoc, collections);

if (!pop(json, MODE_ARRAY)) {
if (!pop(json, Mode::ARRAY)) {
s_json_parser->error_code = JSON_ERROR_STATE_MISMATCH;
return false;
}
Expand All @@ -826,17 +806,17 @@ bool JSON_parser(Variant &z, const char *p, int length, bool const assoc,
"
*/
case -4:
switch (json->stack[json->top]) {
case MODE_KEY:
switch (json->stack[json->top].mode) {
case Mode::KEY:
state = 27;
std::swap(buf, key);
reset_type();
break;
case MODE_ARRAY:
case MODE_OBJECT:
case Mode::ARRAY:
case Mode::OBJECT:
state = 9;
break;
case MODE_DONE:
case Mode::DONE:
if (type == KindOfString) {
z = copy_and_clear(*buf);
state = 9;
Expand All @@ -855,25 +835,25 @@ bool JSON_parser(Variant &z, const char *p, int length, bool const assoc,
{
Variant mval;
if (type != -1 &&
(json->stack[json->top] == MODE_OBJECT ||
json->stack[json->top] == MODE_ARRAY)) {
(json->stack[json->top].mode == Mode::OBJECT ||
json->stack[json->top].mode == Mode::ARRAY)) {
json_create_zval(mval, *buf, type, options);
}

switch (json->stack[json->top]) {
case MODE_OBJECT:
if (pop(json, MODE_OBJECT) &&
push(json, MODE_KEY)) {
switch (json->stack[json->top].mode) {
case Mode::OBJECT:
if (pop(json, Mode::OBJECT) &&
push(json, Mode::KEY)) {
if (type != -1) {
Variant &top = json->zstack[json->top];
Variant &top = json->stack[json->top].val;
object_set(top, copy_and_clear(*key), mval, assoc, collections);
}
state = 29;
}
break;
case MODE_ARRAY:
case Mode::ARRAY:
if (type != -1) {
auto& top = json->zstack[json->top];
auto& top = json->stack[json->top].val;
if (collections) {
collections::append(top.getObjectData(), mval.asCell());
} else {
Expand All @@ -897,7 +877,7 @@ bool JSON_parser(Variant &z, const char *p, int length, bool const assoc,
: (after unquoted string)
*/
case -10:
if (json->stack[json->top] == MODE_KEY) {
if (json->stack[json->top].mode == Mode::KEY) {
state = 27;
std::swap(buf, key);
reset_type();
Expand All @@ -912,7 +892,7 @@ bool JSON_parser(Variant &z, const char *p, int length, bool const assoc,
:
*/
case -2:
if (pop(json, MODE_KEY) && push(json, MODE_OBJECT)) {
if (pop(json, Mode::KEY) && push(json, Mode::OBJECT)) {
state = 28;
break;
}
Expand Down Expand Up @@ -983,7 +963,7 @@ bool JSON_parser(Variant &z, const char *p, int length, bool const assoc,
}
}

if (state == 9 && pop(json, MODE_DONE)) {
if (state == 9 && pop(json, Mode::DONE)) {
s_json_parser->error_code = JSON_ERROR_NONE;
return true;
}
Expand Down

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