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8260030: Improve stringStream buffer handling
Reviewed-by: iklam, kbarrett
  • Loading branch information
tstuefe committed Jan 22, 2021
1 parent 1452280 commit d066f2b06c08d41e47cd7a4b1f047f40df1a5972
Showing with 96 additions and 67 deletions.
  1. +65 −38 src/hotspot/share/utilities/ostream.cpp
  2. +11 −9 src/hotspot/share/utilities/ostream.hpp
  3. +20 −20 test/hotspot/gtest/utilities/test_ostream.cpp
@@ -310,46 +310,72 @@ void outputStream::print_data(void* data, size_t len, bool with_ascii) {
}
}

stringStream::stringStream(size_t initial_size) : outputStream() {
buffer_length = initial_size;
buffer = NEW_C_HEAP_ARRAY(char, buffer_length, mtInternal);
buffer_pos = 0;
buffer_fixed = false;
stringStream::stringStream(size_t initial_capacity) :
outputStream(),
_buffer(_small_buffer),
_written(0),
_capacity(sizeof(_small_buffer)),
_is_fixed(false)
{
if (initial_capacity > _capacity) {
grow(initial_capacity);
}
zero_terminate();
}

// useful for output to fixed chunks of memory, such as performance counters
stringStream::stringStream(char* fixed_buffer, size_t fixed_buffer_size) : outputStream() {
buffer_length = fixed_buffer_size;
buffer = fixed_buffer;
buffer_pos = 0;
buffer_fixed = true;
stringStream::stringStream(char* fixed_buffer, size_t fixed_buffer_size) :
outputStream(),
_buffer(fixed_buffer),
_written(0),
_capacity(fixed_buffer_size),
_is_fixed(true)
{
zero_terminate();
}

// Grow backing buffer to desired capacity. Don't call for fixed buffers
void stringStream::grow(size_t new_capacity) {
assert(!_is_fixed, "Don't call for caller provided buffers");
assert(new_capacity > _capacity, "Sanity");
assert(new_capacity > sizeof(_small_buffer), "Sanity");
if (_buffer == _small_buffer) {
_buffer = NEW_C_HEAP_ARRAY(char, new_capacity, mtInternal);
_capacity = new_capacity;
if (_written > 0) {
::memcpy(_buffer, _small_buffer, _written);
}
zero_terminate();
} else {
_buffer = REALLOC_C_HEAP_ARRAY(char, _buffer, new_capacity, mtInternal);
_capacity = new_capacity;
}
}

void stringStream::write(const char* s, size_t len) {
size_t write_len = len; // number of non-null bytes to write
size_t end = buffer_pos + len + 1; // position after write and final '\0'
if (end > buffer_length) {
if (buffer_fixed) {
// if buffer cannot resize, silently truncate
end = buffer_length;
write_len = end - buffer_pos - 1; // leave room for the final '\0'
} else {
// For small overruns, double the buffer. For larger ones,
// increase to the requested size.
if (end < buffer_length * 2) {
end = buffer_length * 2;
}
buffer = REALLOC_C_HEAP_ARRAY(char, buffer, end, mtInternal);
buffer_length = end;
assert(_capacity >= _written + 1, "Sanity");
if (len == 0) {
return;
}
const size_t reasonable_max_len = 1 * G;
if (len >= reasonable_max_len) {
assert(false, "bad length? (" SIZE_FORMAT ")", len);
return;
}
size_t write_len = 0;
if (_is_fixed) {
write_len = MIN2(len, _capacity - _written - 1);
} else {
write_len = len;
size_t needed = _written + len + 1;
if (needed > _capacity) {
grow(MAX2(needed, _capacity * 2));
}
}
// invariant: buffer is always null-terminated
guarantee(buffer_pos + write_len + 1 <= buffer_length, "stringStream oob");
assert(_written + write_len + 1 <= _capacity, "stringStream oob");
if (write_len > 0) {
memcpy(buffer + buffer_pos, s, write_len);
buffer_pos += write_len;
::memcpy(_buffer + _written, s, write_len);
_written += write_len;
zero_terminate();
}

@@ -360,21 +386,22 @@ void stringStream::write(const char* s, size_t len) {
}

void stringStream::zero_terminate() {
assert(buffer != NULL &&
buffer_pos < buffer_length, "sanity");
buffer[buffer_pos] = '\0';
assert(_buffer != NULL &&
_written < _capacity, "sanity");
_buffer[_written] = '\0';
}

void stringStream::reset() {
buffer_pos = 0; _precount = 0; _position = 0;
_written = 0; _precount = 0; _position = 0;
_newlines = 0;
zero_terminate();
}

char* stringStream::as_string(bool c_heap) const {
char* copy = c_heap ?
NEW_C_HEAP_ARRAY(char, buffer_pos + 1, mtInternal) : NEW_RESOURCE_ARRAY(char, buffer_pos + 1);
strncpy(copy, buffer, buffer_pos);
copy[buffer_pos] = 0; // terminating null
NEW_C_HEAP_ARRAY(char, _written + 1, mtInternal) : NEW_RESOURCE_ARRAY(char, _written + 1);
::memcpy(copy, _buffer, _written);
copy[_written] = 0; // terminating null
if (c_heap) {
// Need to ensure our content is written to memory before we return
// the pointer to it.
@@ -384,8 +411,8 @@ char* stringStream::as_string(bool c_heap) const {
}

stringStream::~stringStream() {
if (buffer_fixed == false && buffer != NULL) {
FREE_C_HEAP_ARRAY(char, buffer);
if (!_is_fixed && _buffer != _small_buffer) {
FREE_C_HEAP_ARRAY(char, _buffer);
}
}

@@ -87,7 +87,6 @@ class outputStream : public ResourceObj {
// sizing
int width() const { return _width; }
int position() const { return _position; }
int newlines() const { return _newlines; }
julong count() const { return _precount + _position; }
void set_count(julong count) { _precount = count - _position; }
void set_position(int pos) { _position = pos; }
@@ -192,28 +191,31 @@ class ttyUnlocker: StackObj {
// for writing to strings; buffer will expand automatically.
// Buffer will always be zero-terminated.
class stringStream : public outputStream {
protected:
char* buffer;
size_t buffer_pos;
size_t buffer_length;
bool buffer_fixed;
char* _buffer;
size_t _written; // Number of characters written, excluding termin. zero
size_t _capacity;
const bool _is_fixed;
char _small_buffer[48];

// Grow backing buffer to desired capacity.
void grow(size_t new_capacity);

// zero terminate at buffer_pos.
void zero_terminate();

public:
// Create a stringStream using an internal buffer of initially initial_bufsize size;
// will be enlarged on demand. There is no maximum cap.
stringStream(size_t initial_bufsize = 256);
stringStream(size_t initial_capacity = 0);
// Creates a stringStream using a caller-provided buffer. Will truncate silently if
// it overflows.
stringStream(char* fixed_buffer, size_t fixed_buffer_size);
~stringStream();
virtual void write(const char* c, size_t len);
// Return number of characters written into buffer, excluding terminating zero and
// subject to truncation in static buffer mode.
size_t size() const { return buffer_pos; }
const char* base() const { return buffer; }
size_t size() const { return _written; }
const char* base() const { return _buffer; }
void reset();
// copy to a resource, or C-heap, array as requested
char* as_string(bool c_heap = false) const;
@@ -31,20 +31,17 @@

#include "unittest.hpp"

static size_t print_lorem(outputStream* st, bool short_len) {
static size_t print_lorem(outputStream* st) {
// Create a ResourceMark just to make sure the stream does not use ResourceArea
ResourceMark rm;
static const char* const lorem = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, "
"sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Lacinia at quis "
"risus sed vulputate odio ut enim blandit. Amet risus nullam eget felis eget. Viverra "
"orci sagittis eu volutpat odio facilisis mauris sit. Erat velit scelerisque in dictum non.";
static const size_t len_lorem = strlen(lorem);
size_t len;
if (short_len) {
len = os::random() % 10;
} else {
len = MAX2(1, (int)(os::random() % len_lorem));
}
// Randomly alternate between short and long writes at a ratio of 9:1.
const bool short_write = (os::random() % 10) > 0;
const size_t len = os::random() % (short_write ? 10 : len_lorem);
st->write(lorem, len);
return len;
}
@@ -53,12 +50,11 @@ static void test_stringStream_is_zero_terminated(const stringStream* ss) {
ASSERT_EQ(ss->base()[ss->size()], '\0');
}


static void do_test_stringStream(stringStream* ss, bool short_len, size_t expected_cap) {
static void do_test_stringStream(stringStream* ss, size_t expected_cap) {
test_stringStream_is_zero_terminated(ss);
size_t written = 0;
for (int i = 0; i < 1000; i ++) {
written += print_lorem(ss, short_len);
written += print_lorem(ss);
if (expected_cap > 0 && written >= expected_cap) {
ASSERT_EQ(ss->size(), expected_cap - 1);
} else {
@@ -73,14 +69,18 @@ static void do_test_stringStream(stringStream* ss, bool short_len, size_t expect
test_stringStream_is_zero_terminated(ss);
}

TEST_VM(ostream, stringStream_dynamic_realloc_1) {
stringStream ss(2); // dynamic buffer with very small starting size
do_test_stringStream(&ss, false, 0);
TEST_VM(ostream, stringStream_dynamic_start_with_internal_buffer) {
stringStream ss;
do_test_stringStream(&ss, 0);
ss.reset();
do_test_stringStream(&ss, 0);
}

TEST_VM(ostream, stringStream_dynamic_realloc_2) {
stringStream ss(2); // dynamic buffer with very small starting size
do_test_stringStream(&ss, true, 0);
TEST_VM(ostream, stringStream_dynamic_start_with_malloced_buffer) {
stringStream ss(128);
do_test_stringStream(&ss, 0);
ss.reset();
do_test_stringStream(&ss, 0);
}

TEST_VM(ostream, stringStream_static) {
@@ -89,7 +89,7 @@ TEST_VM(ostream, stringStream_static) {
*canary_at = 'X';
size_t stream_buf_size = sizeof(buffer) - 1;
stringStream ss(buffer, stream_buf_size);
do_test_stringStream(&ss, false, stream_buf_size);
do_test_stringStream(&ss, stream_buf_size);
ASSERT_EQ(*canary_at, 'X'); // canary
}

@@ -101,7 +101,7 @@ TEST_VM(ostream, bufferedStream_static) {
bufferedStream bs(buf, stream_buf_size);
size_t written = 0;
for (int i = 0; i < 100; i ++) {
written += print_lorem(&bs, true);
written += print_lorem(&bs);
if (written < stream_buf_size) {
ASSERT_EQ(bs.size(), written);
} else {
@@ -116,7 +116,7 @@ TEST_VM(ostream, bufferedStream_dynamic_small) {
size_t written = 0;
// The max cap imposed is 100M, we should be safely below this in this test.
for (int i = 0; i < 10; i ++) {
written += print_lorem(&bs, true);
written += print_lorem(&bs);
ASSERT_EQ(bs.size(), written);
}
}
@@ -130,7 +130,7 @@ TEST_VM(ostream, bufferedStream_dynamic_large) {
// Note that this will assert in debug builds which is the expected behavior.
size_t expected_cap_at = 100 * M;
for (int i = 0; i < 10000000; i ++) {
written += print_lorem(&bs, false);
written += print_lorem(&bs);
if (written < expected_cap_at) {
ASSERT_EQ(bs.size(), written);
} else {

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