fbstring IOBuf::moveToFbString() {
// malloc-allocated buffers are just fine, everything else needs
// to be turned into one.
if (!sharedInfo() || // user owned, not ours to give up
sharedInfo()->freeFn || // not malloc()-ed
headroom() != 0 || // malloc()-ed block doesn't start at beginning
tailroom() == 0 || // no room for NUL terminator
isShared() || // shared
isChained()) { // chained
// We might as well get rid of all head and tailroom if we're going
// to reallocate; we need 1 byte for NUL terminator.
coalesceAndReallocate(0, computeChainDataLength(), this, 1);
}
// Ensure NUL terminated
*writableTail() = 0;
fbstring str(reinterpret_cast<char*>(writableData()),
length(), capacity(),
AcquireMallocatedString());
if (flags() & kFlagFreeSharedInfo) {
delete sharedInfo();
}
// Reset to a state where we can be deleted cleanly
flagsAndSharedInfo_ = 0;
buf_ = nullptr;
clear();
return str;
}
void IOBuf::unshareOneSlow() {
// Allocate a new buffer for the data
uint8_t* buf;
SharedInfo* sharedInfo;
uint64_t actualCapacity;
allocExtBuffer(capacity_, &buf, &sharedInfo, &actualCapacity);
// Copy the data
// Maintain the same amount of headroom. Since we maintained the same
// minimum capacity we also maintain at least the same amount of tailroom.
uint64_t headlen = headroom();
if (length_ > 0) {
assert(data_ != nullptr);
memcpy(buf + headlen, data_, length_);
}
// Release our reference on the old buffer
decrementRefcount();
// Make sure kFlagMaybeShared and kFlagFreeSharedInfo are all cleared.
setFlagsAndSharedInfo(0, sharedInfo);
// Update the buffer pointers to point to the new buffer
data_ = buf + headlen;
buf_ = buf;
}
IOBuf IOBuf::cloneCoalescedAsValue() const {
if (!isChained()) {
return cloneOneAsValue();
}
// Coalesce into newBuf
const uint64_t newLength = computeChainDataLength();
const uint64_t newHeadroom = headroom();
const uint64_t newTailroom = prev()->tailroom();
const uint64_t newCapacity = newLength + newHeadroom + newTailroom;
IOBuf newBuf{CREATE, newCapacity};
newBuf.advance(newHeadroom);
auto current = this;
do {
if (current->length() > 0) {
DCHECK_NOTNULL(current->data());
DCHECK_LE(current->length(), newBuf.tailroom());
memcpy(newBuf.writableTail(), current->data(), current->length());
newBuf.append(current->length());
}
current = current->next();
} while (current != this);
DCHECK_EQ(newLength, newBuf.length());
DCHECK_EQ(newHeadroom, newBuf.headroom());
DCHECK_LE(newTailroom, newBuf.tailroom());
return newBuf;
}
void
IOBufQueue::prepend(const void* buf, uint64_t n) {
auto p = headroom();
if (n > p.second) {
throw std::overflow_error("Not enough room to prepend");
}
memcpy(static_cast<char*>(p.first) + p.second - n, buf, n);
markPrepended(n);
}
void IOBuf::unshareOneSlow() {
// Allocate a new buffer for the data
uint8_t* buf;
SharedInfo* sharedInfo;
uint32_t actualCapacity;
allocExtBuffer(capacity_, &buf, &sharedInfo, &actualCapacity);
// Copy the data
// Maintain the same amount of headroom. Since we maintained the same
// minimum capacity we also maintain at least the same amount of tailroom.
uint32_t headlen = headroom();
memcpy(buf + headlen, data_, length_);
// Release our reference on the old buffer
decrementRefcount();
// Make sure kFlagUserOwned, kFlagMaybeShared, and kFlagFreeSharedInfo
// are all cleared.
flags_ = 0;
// Update the buffer pointers to point to the new buffer
data_ = buf + headlen;
buf_ = buf;
sharedInfo_ = sharedInfo;
}
void IOBuf::reserveSlow(uint64_t minHeadroom, uint64_t minTailroom) {
size_t newCapacity = (size_t)length_ + minHeadroom + minTailroom;
DCHECK_LT(newCapacity, UINT32_MAX);
// reserveSlow() is dangerous if anyone else is sharing the buffer, as we may
// reallocate and free the original buffer. It should only ever be called if
// we are the only user of the buffer.
DCHECK(!isSharedOne());
// We'll need to reallocate the buffer.
// There are a few options.
// - If we have enough total room, move the data around in the buffer
// and adjust the data_ pointer.
// - If we're using an internal buffer, we'll switch to an external
// buffer with enough headroom and tailroom.
// - If we have enough headroom (headroom() >= minHeadroom) but not too much
// (so we don't waste memory), we can try one of two things, depending on
// whether we use jemalloc or not:
// - If using jemalloc, we can try to expand in place, avoiding a memcpy()
// - If not using jemalloc and we don't have too much to copy,
// we'll use realloc() (note that realloc might have to copy
// headroom + data + tailroom, see smartRealloc in folly/Malloc.h)
// - Otherwise, bite the bullet and reallocate.
if (headroom() + tailroom() >= minHeadroom + minTailroom) {
uint8_t* newData = writableBuffer() + minHeadroom;
memmove(newData, data_, length_);
data_ = newData;
return;
}
size_t newAllocatedCapacity = 0;
uint8_t* newBuffer = nullptr;
uint64_t newHeadroom = 0;
uint64_t oldHeadroom = headroom();
// If we have a buffer allocated with malloc and we just need more tailroom,
// try to use realloc()/xallocx() to grow the buffer in place.
SharedInfo* info = sharedInfo();
if (info && (info->freeFn == nullptr) && length_ != 0 &&
oldHeadroom >= minHeadroom) {
size_t headSlack = oldHeadroom - minHeadroom;
newAllocatedCapacity = goodExtBufferSize(newCapacity + headSlack);
if (usingJEMalloc()) {
// We assume that tailroom is more useful and more important than
// headroom (not least because realloc / xallocx allow us to grow the
// buffer at the tail, but not at the head) So, if we have more headroom
// than we need, we consider that "wasted". We arbitrarily define "too
// much" headroom to be 25% of the capacity.
if (headSlack * 4 <= newCapacity) {
size_t allocatedCapacity = capacity() + sizeof(SharedInfo);
void* p = buf_;
if (allocatedCapacity >= jemallocMinInPlaceExpandable) {
if (xallocx(p, newAllocatedCapacity, 0, 0) == newAllocatedCapacity) {
newBuffer = static_cast<uint8_t*>(p);
newHeadroom = oldHeadroom;
}
// if xallocx failed, do nothing, fall back to malloc/memcpy/free
}
}
} else { // Not using jemalloc
size_t copySlack = capacity() - length_;
if (copySlack * 2 <= length_) {
void* p = realloc(buf_, newAllocatedCapacity);
if (UNLIKELY(p == nullptr)) {
throw std::bad_alloc();
}
newBuffer = static_cast<uint8_t*>(p);
newHeadroom = oldHeadroom;
}
}
}
// None of the previous reallocation strategies worked (or we're using
// an internal buffer). malloc/copy/free.
if (newBuffer == nullptr) {
newAllocatedCapacity = goodExtBufferSize(newCapacity);
void* p = malloc(newAllocatedCapacity);
if (UNLIKELY(p == nullptr)) {
throw std::bad_alloc();
}
newBuffer = static_cast<uint8_t*>(p);
if (length_ > 0) {
assert(data_ != nullptr);
memcpy(newBuffer + minHeadroom, data_, length_);
}
if (sharedInfo()) {
freeExtBuffer();
}
newHeadroom = minHeadroom;
}
uint64_t cap;
initExtBuffer(newBuffer, newAllocatedCapacity, &info, &cap);
if (flags() & kFlagFreeSharedInfo) {
delete sharedInfo();
}
setFlagsAndSharedInfo(0, info);
capacity_ = cap;
buf_ = newBuffer;
data_ = newBuffer + newHeadroom;
// length_ is unchanged
}
