2 * Copyright 2016 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 #ifndef __STDC_LIMIT_MACROS
18 #define __STDC_LIMIT_MACROS
21 #include <folly/io/IOBuf.h>
23 #include <folly/Conv.h>
24 #include <folly/Likely.h>
25 #include <folly/Malloc.h>
26 #include <folly/Memory.h>
27 #include <folly/ScopeGuard.h>
28 #include <folly/SpookyHashV2.h>
29 #include <folly/io/Cursor.h>
36 using std::unique_ptr;
42 // This memory segment contains an IOBuf that is still in use
44 // This memory segment contains buffer data that is still in use
49 // When create() is called for buffers less than kDefaultCombinedBufSize,
50 // we allocate a single combined memory segment for the IOBuf and the data
51 // together. See the comments for createCombined()/createSeparate() for more
54 // (The size of 1k is largely just a guess here. We could could probably do
55 // benchmarks of real applications to see if adjusting this number makes a
56 // difference. Callers that know their exact use case can also explicitly
57 // call createCombined() or createSeparate().)
58 kDefaultCombinedBufSize = 1024
61 // Helper function for IOBuf::takeOwnership()
62 void takeOwnershipError(bool freeOnError, void* buf,
63 folly::IOBuf::FreeFunction freeFn,
73 freeFn(buf, userData);
75 // The user's free function is not allowed to throw.
76 // (We are already in the middle of throwing an exception, so
77 // we cannot let this exception go unhandled.)
82 } // unnamed namespace
86 struct IOBuf::HeapPrefix {
87 HeapPrefix(uint16_t flg)
91 // Reset magic to 0 on destruction. This is solely for debugging purposes
92 // to help catch bugs where someone tries to use HeapStorage after it has
98 std::atomic<uint16_t> flags;
101 struct IOBuf::HeapStorage {
103 // The IOBuf is last in the HeapStorage object.
104 // This way operator new will work even if allocating a subclass of IOBuf
105 // that requires more space.
109 struct IOBuf::HeapFullStorage {
110 // Make sure jemalloc allocates from the 64-byte class. Putting this here
111 // because HeapStorage is private so it can't be at namespace level.
112 static_assert(sizeof(HeapStorage) <= 64,
113 "IOBuf may not grow over 56 bytes!");
117 std::max_align_t align;
120 IOBuf::SharedInfo::SharedInfo()
123 // Use relaxed memory ordering here. Since we are creating a new SharedInfo,
124 // no other threads should be referring to it yet.
125 refcount.store(1, std::memory_order_relaxed);
128 IOBuf::SharedInfo::SharedInfo(FreeFunction fn, void* arg)
131 // Use relaxed memory ordering here. Since we are creating a new SharedInfo,
132 // no other threads should be referring to it yet.
133 refcount.store(1, std::memory_order_relaxed);
136 void* IOBuf::operator new(size_t size) {
137 size_t fullSize = offsetof(HeapStorage, buf) + size;
138 auto* storage = static_cast<HeapStorage*>(malloc(fullSize));
139 // operator new is not allowed to return NULL
140 if (UNLIKELY(storage == nullptr)) {
141 throw std::bad_alloc();
144 new (&storage->prefix) HeapPrefix(kIOBufInUse);
145 return &(storage->buf);
148 void* IOBuf::operator new(size_t /* size */, void* ptr) { return ptr; }
150 void IOBuf::operator delete(void* ptr) {
151 auto* storageAddr = static_cast<uint8_t*>(ptr) - offsetof(HeapStorage, buf);
152 auto* storage = reinterpret_cast<HeapStorage*>(storageAddr);
153 releaseStorage(storage, kIOBufInUse);
156 void IOBuf::releaseStorage(HeapStorage* storage, uint16_t freeFlags) {
157 CHECK_EQ(storage->prefix.magic, static_cast<uint16_t>(kHeapMagic));
159 // Use relaxed memory order here. If we are unlucky and happen to get
160 // out-of-date data the compare_exchange_weak() call below will catch
161 // it and load new data with memory_order_acq_rel.
162 auto flags = storage->prefix.flags.load(std::memory_order_acquire);
163 DCHECK_EQ((flags & freeFlags), freeFlags);
166 uint16_t newFlags = (flags & ~freeFlags);
168 // The storage space is now unused. Free it.
169 storage->prefix.HeapPrefix::~HeapPrefix();
174 // This storage segment still contains portions that are in use.
175 // Just clear the flags specified in freeFlags for now.
176 auto ret = storage->prefix.flags.compare_exchange_weak(
177 flags, newFlags, std::memory_order_acq_rel);
179 // We successfully updated the flags.
183 // We failed to update the flags. Some other thread probably updated them
184 // and cleared some of the other bits. Continue around the loop to see if
185 // we are the last user now, or if we need to try updating the flags again.
189 void IOBuf::freeInternalBuf(void* /* buf */, void* userData) {
190 auto* storage = static_cast<HeapStorage*>(userData);
191 releaseStorage(storage, kDataInUse);
194 IOBuf::IOBuf(CreateOp, uint64_t capacity)
199 flagsAndSharedInfo_(0) {
201 allocExtBuffer(capacity, &buf_, &info, &capacity_);
206 IOBuf::IOBuf(CopyBufferOp /* op */,
210 uint64_t minTailroom)
211 : IOBuf(CREATE, headroom + size + minTailroom) {
213 memcpy(writableData(), buf, size);
217 IOBuf::IOBuf(CopyBufferOp op, ByteRange br,
218 uint64_t headroom, uint64_t minTailroom)
219 : IOBuf(op, br.data(), br.size(), headroom, minTailroom) {
222 unique_ptr<IOBuf> IOBuf::create(uint64_t capacity) {
223 // For smaller-sized buffers, allocate the IOBuf, SharedInfo, and the buffer
224 // all with a single allocation.
226 // We don't do this for larger buffers since it can be wasteful if the user
227 // needs to reallocate the buffer but keeps using the same IOBuf object.
228 // In this case we can't free the data space until the IOBuf is also
229 // destroyed. Callers can explicitly call createCombined() or
230 // createSeparate() if they know their use case better, and know if they are
231 // likely to reallocate the buffer later.
232 if (capacity <= kDefaultCombinedBufSize) {
233 return createCombined(capacity);
235 return createSeparate(capacity);
238 unique_ptr<IOBuf> IOBuf::createCombined(uint64_t capacity) {
239 // To save a memory allocation, allocate space for the IOBuf object, the
240 // SharedInfo struct, and the data itself all with a single call to malloc().
241 size_t requiredStorage = offsetof(HeapFullStorage, align) + capacity;
242 size_t mallocSize = goodMallocSize(requiredStorage);
243 auto* storage = static_cast<HeapFullStorage*>(malloc(mallocSize));
245 new (&storage->hs.prefix) HeapPrefix(kIOBufInUse | kDataInUse);
246 new (&storage->shared) SharedInfo(freeInternalBuf, storage);
248 uint8_t* bufAddr = reinterpret_cast<uint8_t*>(&storage->align);
249 uint8_t* storageEnd = reinterpret_cast<uint8_t*>(storage) + mallocSize;
250 size_t actualCapacity = storageEnd - bufAddr;
251 unique_ptr<IOBuf> ret(new (&storage->hs.buf) IOBuf(
252 InternalConstructor(), packFlagsAndSharedInfo(0, &storage->shared),
253 bufAddr, actualCapacity, bufAddr, 0));
257 unique_ptr<IOBuf> IOBuf::createSeparate(uint64_t capacity) {
258 return make_unique<IOBuf>(CREATE, capacity);
261 unique_ptr<IOBuf> IOBuf::createChain(
262 size_t totalCapacity, uint64_t maxBufCapacity) {
263 unique_ptr<IOBuf> out = create(
264 std::min(totalCapacity, size_t(maxBufCapacity)));
265 size_t allocatedCapacity = out->capacity();
267 while (allocatedCapacity < totalCapacity) {
268 unique_ptr<IOBuf> newBuf = create(
269 std::min(totalCapacity - allocatedCapacity, size_t(maxBufCapacity)));
270 allocatedCapacity += newBuf->capacity();
271 out->prependChain(std::move(newBuf));
277 IOBuf::IOBuf(TakeOwnershipOp, void* buf, uint64_t capacity, uint64_t length,
278 FreeFunction freeFn, void* userData,
282 data_(static_cast<uint8_t*>(buf)),
283 buf_(static_cast<uint8_t*>(buf)),
286 flagsAndSharedInfo_(packFlagsAndSharedInfo(kFlagFreeSharedInfo, nullptr)) {
288 setSharedInfo(new SharedInfo(freeFn, userData));
290 takeOwnershipError(freeOnError, buf, freeFn, userData);
295 unique_ptr<IOBuf> IOBuf::takeOwnership(void* buf, uint64_t capacity,
301 // TODO: We could allocate the IOBuf object and SharedInfo all in a single
302 // memory allocation. We could use the existing HeapStorage class, and
303 // define a new kSharedInfoInUse flag. We could change our code to call
304 // releaseStorage(kFlagFreeSharedInfo) when this kFlagFreeSharedInfo,
305 // rather than directly calling delete.
307 // Note that we always pass freeOnError as false to the constructor.
308 // If the constructor throws we'll handle it below. (We have to handle
309 // allocation failures from make_unique too.)
310 return make_unique<IOBuf>(TAKE_OWNERSHIP, buf, capacity, length,
311 freeFn, userData, false);
313 takeOwnershipError(freeOnError, buf, freeFn, userData);
318 IOBuf::IOBuf(WrapBufferOp, const void* buf, uint64_t capacity)
319 : IOBuf(InternalConstructor(), 0,
320 // We cast away the const-ness of the buffer here.
321 // This is okay since IOBuf users must use unshare() to create a copy
322 // of this buffer before writing to the buffer.
323 static_cast<uint8_t*>(const_cast<void*>(buf)), capacity,
324 static_cast<uint8_t*>(const_cast<void*>(buf)), capacity) {
327 IOBuf::IOBuf(WrapBufferOp op, ByteRange br)
328 : IOBuf(op, br.data(), br.size()) {
331 unique_ptr<IOBuf> IOBuf::wrapBuffer(const void* buf, uint64_t capacity) {
332 return make_unique<IOBuf>(WRAP_BUFFER, buf, capacity);
335 IOBuf IOBuf::wrapBufferAsValue(const void* buf, uint64_t capacity) {
336 return IOBuf(WrapBufferOp::WRAP_BUFFER, buf, capacity);
339 IOBuf::IOBuf() noexcept {
342 IOBuf::IOBuf(IOBuf&& other) noexcept
343 : data_(other.data_),
345 length_(other.length_),
346 capacity_(other.capacity_),
347 flagsAndSharedInfo_(other.flagsAndSharedInfo_) {
348 // Reset other so it is a clean state to be destroyed.
349 other.data_ = nullptr;
350 other.buf_ = nullptr;
353 other.flagsAndSharedInfo_ = 0;
355 // If other was part of the chain, assume ownership of the rest of its chain.
356 // (It's only valid to perform move assignment on the head of a chain.)
357 if (other.next_ != &other) {
360 other.next_ = &other;
364 other.prev_ = &other;
367 // Sanity check to make sure that other is in a valid state to be destroyed.
368 DCHECK_EQ(other.prev_, &other);
369 DCHECK_EQ(other.next_, &other);
372 IOBuf::IOBuf(const IOBuf& other) {
373 *this = other.cloneAsValue();
376 IOBuf::IOBuf(InternalConstructor,
377 uintptr_t flagsAndSharedInfo,
388 flagsAndSharedInfo_(flagsAndSharedInfo) {
390 assert(data + length <= buf + capacity);
394 // Destroying an IOBuf destroys the entire chain.
395 // Users of IOBuf should only explicitly delete the head of any chain.
396 // The other elements in the chain will be automatically destroyed.
397 while (next_ != this) {
398 // Since unlink() returns unique_ptr() and we don't store it,
399 // it will automatically delete the unlinked element.
400 (void)next_->unlink();
406 IOBuf& IOBuf::operator=(IOBuf&& other) noexcept {
407 if (this == &other) {
411 // If we are part of a chain, delete the rest of the chain.
412 while (next_ != this) {
413 // Since unlink() returns unique_ptr() and we don't store it,
414 // it will automatically delete the unlinked element.
415 (void)next_->unlink();
418 // Decrement our refcount on the current buffer
421 // Take ownership of the other buffer's data
424 length_ = other.length_;
425 capacity_ = other.capacity_;
426 flagsAndSharedInfo_ = other.flagsAndSharedInfo_;
427 // Reset other so it is a clean state to be destroyed.
428 other.data_ = nullptr;
429 other.buf_ = nullptr;
432 other.flagsAndSharedInfo_ = 0;
434 // If other was part of the chain, assume ownership of the rest of its chain.
435 // (It's only valid to perform move assignment on the head of a chain.)
436 if (other.next_ != &other) {
439 other.next_ = &other;
443 other.prev_ = &other;
446 // Sanity check to make sure that other is in a valid state to be destroyed.
447 DCHECK_EQ(other.prev_, &other);
448 DCHECK_EQ(other.next_, &other);
453 IOBuf& IOBuf::operator=(const IOBuf& other) {
454 if (this != &other) {
455 *this = IOBuf(other);
460 bool IOBuf::empty() const {
461 const IOBuf* current = this;
463 if (current->length() != 0) {
466 current = current->next_;
467 } while (current != this);
471 size_t IOBuf::countChainElements() const {
472 size_t numElements = 1;
473 for (IOBuf* current = next_; current != this; current = current->next_) {
479 uint64_t IOBuf::computeChainDataLength() const {
480 uint64_t fullLength = length_;
481 for (IOBuf* current = next_; current != this; current = current->next_) {
482 fullLength += current->length_;
487 void IOBuf::prependChain(unique_ptr<IOBuf>&& iobuf) {
488 // Take ownership of the specified IOBuf
489 IOBuf* other = iobuf.release();
491 // Remember the pointer to the tail of the other chain
492 IOBuf* otherTail = other->prev_;
494 // Hook up prev_->next_ to point at the start of the other chain,
495 // and other->prev_ to point at prev_
496 prev_->next_ = other;
497 other->prev_ = prev_;
499 // Hook up otherTail->next_ to point at us,
500 // and prev_ to point back at otherTail,
501 otherTail->next_ = this;
505 unique_ptr<IOBuf> IOBuf::clone() const {
506 return make_unique<IOBuf>(cloneAsValue());
509 unique_ptr<IOBuf> IOBuf::cloneOne() const {
510 return make_unique<IOBuf>(cloneOneAsValue());
513 IOBuf IOBuf::cloneAsValue() const {
514 auto tmp = cloneOneAsValue();
516 for (IOBuf* current = next_; current != this; current = current->next_) {
517 tmp.prependChain(current->cloneOne());
523 IOBuf IOBuf::cloneOneAsValue() const {
524 if (SharedInfo* info = sharedInfo()) {
525 setFlags(kFlagMaybeShared);
526 info->refcount.fetch_add(1, std::memory_order_acq_rel);
529 InternalConstructor(),
537 void IOBuf::unshareOneSlow() {
538 // Allocate a new buffer for the data
540 SharedInfo* sharedInfo;
541 uint64_t actualCapacity;
542 allocExtBuffer(capacity_, &buf, &sharedInfo, &actualCapacity);
545 // Maintain the same amount of headroom. Since we maintained the same
546 // minimum capacity we also maintain at least the same amount of tailroom.
547 uint64_t headlen = headroom();
548 memcpy(buf + headlen, data_, length_);
550 // Release our reference on the old buffer
552 // Make sure kFlagMaybeShared and kFlagFreeSharedInfo are all cleared.
553 setFlagsAndSharedInfo(0, sharedInfo);
555 // Update the buffer pointers to point to the new buffer
556 data_ = buf + headlen;
560 void IOBuf::unshareChained() {
561 // unshareChained() should only be called if we are part of a chain of
562 // multiple IOBufs. The caller should have already verified this.
565 IOBuf* current = this;
567 if (current->isSharedOne()) {
568 // we have to unshare
572 current = current->next_;
573 if (current == this) {
574 // None of the IOBufs in the chain are shared,
575 // so return without doing anything
580 // We have to unshare. Let coalesceSlow() do the work.
584 void IOBuf::markExternallyShared() {
585 IOBuf* current = this;
587 current->markExternallySharedOne();
588 current = current->next_;
589 } while (current != this);
592 void IOBuf::makeManagedChained() {
595 IOBuf* current = this;
597 current->makeManagedOne();
598 current = current->next_;
599 if (current == this) {
605 void IOBuf::coalesceSlow() {
606 // coalesceSlow() should only be called if we are part of a chain of multiple
607 // IOBufs. The caller should have already verified this.
610 // Compute the length of the entire chain
611 uint64_t newLength = 0;
614 newLength += end->length_;
616 } while (end != this);
618 coalesceAndReallocate(newLength, end);
619 // We should be only element left in the chain now
620 DCHECK(!isChained());
623 void IOBuf::coalesceSlow(size_t maxLength) {
624 // coalesceSlow() should only be called if we are part of a chain of multiple
625 // IOBufs. The caller should have already verified this.
627 DCHECK_LT(length_, maxLength);
629 // Compute the length of the entire chain
630 uint64_t newLength = 0;
633 newLength += end->length_;
635 if (newLength >= maxLength) {
639 throw std::overflow_error("attempted to coalesce more data than "
644 coalesceAndReallocate(newLength, end);
645 // We should have the requested length now
646 DCHECK_GE(length_, maxLength);
649 void IOBuf::coalesceAndReallocate(size_t newHeadroom,
652 size_t newTailroom) {
653 uint64_t newCapacity = newLength + newHeadroom + newTailroom;
655 // Allocate space for the coalesced buffer.
656 // We always convert to an external buffer, even if we happened to be an
657 // internal buffer before.
660 uint64_t actualCapacity;
661 allocExtBuffer(newCapacity, &newBuf, &newInfo, &actualCapacity);
663 // Copy the data into the new buffer
664 uint8_t* newData = newBuf + newHeadroom;
665 uint8_t* p = newData;
666 IOBuf* current = this;
667 size_t remaining = newLength;
669 assert(current->length_ <= remaining);
670 remaining -= current->length_;
671 memcpy(p, current->data_, current->length_);
672 p += current->length_;
673 current = current->next_;
674 } while (current != end);
675 assert(remaining == 0);
677 // Point at the new buffer
680 // Make sure kFlagMaybeShared and kFlagFreeSharedInfo are all cleared.
681 setFlagsAndSharedInfo(0, newInfo);
683 capacity_ = actualCapacity;
688 // Separate from the rest of our chain.
689 // Since we don't store the unique_ptr returned by separateChain(),
690 // this will immediately delete the returned subchain.
692 (void)separateChain(next_, current->prev_);
696 void IOBuf::decrementRefcount() {
697 // Externally owned buffers don't have a SharedInfo object and aren't managed
698 // by the reference count
699 SharedInfo* info = sharedInfo();
704 // Decrement the refcount
705 uint32_t newcnt = info->refcount.fetch_sub(
706 1, std::memory_order_acq_rel);
707 // Note that fetch_sub() returns the value before we decremented.
708 // If it is 1, we were the only remaining user; if it is greater there are
709 // still other users.
714 // We were the last user. Free the buffer
717 // Free the SharedInfo if it was allocated separately.
719 // This is only used by takeOwnership().
721 // To avoid this special case handling in decrementRefcount(), we could have
722 // takeOwnership() set a custom freeFn() that calls the user's free function
723 // then frees the SharedInfo object. (This would require that
724 // takeOwnership() store the user's free function with its allocated
725 // SharedInfo object.) However, handling this specially with a flag seems
726 // like it shouldn't be problematic.
727 if (flags() & kFlagFreeSharedInfo) {
732 void IOBuf::reserveSlow(uint64_t minHeadroom, uint64_t minTailroom) {
733 size_t newCapacity = (size_t)length_ + minHeadroom + minTailroom;
734 DCHECK_LT(newCapacity, UINT32_MAX);
736 // reserveSlow() is dangerous if anyone else is sharing the buffer, as we may
737 // reallocate and free the original buffer. It should only ever be called if
738 // we are the only user of the buffer.
739 DCHECK(!isSharedOne());
741 // We'll need to reallocate the buffer.
742 // There are a few options.
743 // - If we have enough total room, move the data around in the buffer
744 // and adjust the data_ pointer.
745 // - If we're using an internal buffer, we'll switch to an external
746 // buffer with enough headroom and tailroom.
747 // - If we have enough headroom (headroom() >= minHeadroom) but not too much
748 // (so we don't waste memory), we can try one of two things, depending on
749 // whether we use jemalloc or not:
750 // - If using jemalloc, we can try to expand in place, avoiding a memcpy()
751 // - If not using jemalloc and we don't have too much to copy,
752 // we'll use realloc() (note that realloc might have to copy
753 // headroom + data + tailroom, see smartRealloc in folly/Malloc.h)
754 // - Otherwise, bite the bullet and reallocate.
755 if (headroom() + tailroom() >= minHeadroom + minTailroom) {
756 uint8_t* newData = writableBuffer() + minHeadroom;
757 memmove(newData, data_, length_);
762 size_t newAllocatedCapacity = 0;
763 uint8_t* newBuffer = nullptr;
764 uint64_t newHeadroom = 0;
765 uint64_t oldHeadroom = headroom();
767 // If we have a buffer allocated with malloc and we just need more tailroom,
768 // try to use realloc()/xallocx() to grow the buffer in place.
769 SharedInfo* info = sharedInfo();
770 if (info && (info->freeFn == nullptr) && length_ != 0 &&
771 oldHeadroom >= minHeadroom) {
772 size_t headSlack = oldHeadroom - minHeadroom;
773 newAllocatedCapacity = goodExtBufferSize(newCapacity + headSlack);
774 if (usingJEMalloc()) {
775 // We assume that tailroom is more useful and more important than
776 // headroom (not least because realloc / xallocx allow us to grow the
777 // buffer at the tail, but not at the head) So, if we have more headroom
778 // than we need, we consider that "wasted". We arbitrarily define "too
779 // much" headroom to be 25% of the capacity.
780 if (headSlack * 4 <= newCapacity) {
781 size_t allocatedCapacity = capacity() + sizeof(SharedInfo);
783 if (allocatedCapacity >= jemallocMinInPlaceExpandable) {
784 if (xallocx(p, newAllocatedCapacity, 0, 0) == newAllocatedCapacity) {
785 newBuffer = static_cast<uint8_t*>(p);
786 newHeadroom = oldHeadroom;
788 // if xallocx failed, do nothing, fall back to malloc/memcpy/free
791 } else { // Not using jemalloc
792 size_t copySlack = capacity() - length_;
793 if (copySlack * 2 <= length_) {
794 void* p = realloc(buf_, newAllocatedCapacity);
795 if (UNLIKELY(p == nullptr)) {
796 throw std::bad_alloc();
798 newBuffer = static_cast<uint8_t*>(p);
799 newHeadroom = oldHeadroom;
804 // None of the previous reallocation strategies worked (or we're using
805 // an internal buffer). malloc/copy/free.
806 if (newBuffer == nullptr) {
807 newAllocatedCapacity = goodExtBufferSize(newCapacity);
808 void* p = malloc(newAllocatedCapacity);
809 if (UNLIKELY(p == nullptr)) {
810 throw std::bad_alloc();
812 newBuffer = static_cast<uint8_t*>(p);
813 memcpy(newBuffer + minHeadroom, data_, length_);
817 newHeadroom = minHeadroom;
821 initExtBuffer(newBuffer, newAllocatedCapacity, &info, &cap);
823 if (flags() & kFlagFreeSharedInfo) {
827 setFlagsAndSharedInfo(0, info);
830 data_ = newBuffer + newHeadroom;
831 // length_ is unchanged
834 void IOBuf::freeExtBuffer() {
835 SharedInfo* info = sharedInfo();
840 info->freeFn(buf_, info->userData);
842 // The user's free function should never throw. Otherwise we might
843 // throw from the IOBuf destructor. Other code paths like coalesce()
844 // also assume that decrementRefcount() cannot throw.
852 void IOBuf::allocExtBuffer(uint64_t minCapacity,
854 SharedInfo** infoReturn,
855 uint64_t* capacityReturn) {
856 size_t mallocSize = goodExtBufferSize(minCapacity);
857 uint8_t* buf = static_cast<uint8_t*>(malloc(mallocSize));
858 if (UNLIKELY(buf == nullptr)) {
859 throw std::bad_alloc();
861 initExtBuffer(buf, mallocSize, infoReturn, capacityReturn);
865 size_t IOBuf::goodExtBufferSize(uint64_t minCapacity) {
866 // Determine how much space we should allocate. We'll store the SharedInfo
867 // for the external buffer just after the buffer itself. (We store it just
868 // after the buffer rather than just before so that the code can still just
869 // use free(buf_) to free the buffer.)
870 size_t minSize = static_cast<size_t>(minCapacity) + sizeof(SharedInfo);
871 // Add room for padding so that the SharedInfo will be aligned on an 8-byte
873 minSize = (minSize + 7) & ~7;
875 // Use goodMallocSize() to bump up the capacity to a decent size to request
876 // from malloc, so we can use all of the space that malloc will probably give
878 return goodMallocSize(minSize);
881 void IOBuf::initExtBuffer(uint8_t* buf, size_t mallocSize,
882 SharedInfo** infoReturn,
883 uint64_t* capacityReturn) {
884 // Find the SharedInfo storage at the end of the buffer
885 // and construct the SharedInfo.
886 uint8_t* infoStart = (buf + mallocSize) - sizeof(SharedInfo);
887 SharedInfo* sharedInfo = new(infoStart) SharedInfo;
889 *capacityReturn = infoStart - buf;
890 *infoReturn = sharedInfo;
893 fbstring IOBuf::moveToFbString() {
894 // malloc-allocated buffers are just fine, everything else needs
895 // to be turned into one.
896 if (!sharedInfo() || // user owned, not ours to give up
897 sharedInfo()->freeFn || // not malloc()-ed
898 headroom() != 0 || // malloc()-ed block doesn't start at beginning
899 tailroom() == 0 || // no room for NUL terminator
900 isShared() || // shared
901 isChained()) { // chained
902 // We might as well get rid of all head and tailroom if we're going
903 // to reallocate; we need 1 byte for NUL terminator.
904 coalesceAndReallocate(0, computeChainDataLength(), this, 1);
907 // Ensure NUL terminated
909 fbstring str(reinterpret_cast<char*>(writableData()),
910 length(), capacity(),
911 AcquireMallocatedString());
913 if (flags() & kFlagFreeSharedInfo) {
917 // Reset to a state where we can be deleted cleanly
918 flagsAndSharedInfo_ = 0;
924 IOBuf::Iterator IOBuf::cbegin() const {
925 return Iterator(this, this);
928 IOBuf::Iterator IOBuf::cend() const {
929 return Iterator(nullptr, nullptr);
932 folly::fbvector<struct iovec> IOBuf::getIov() const {
933 folly::fbvector<struct iovec> iov;
934 iov.reserve(countChainElements());
939 void IOBuf::appendToIov(folly::fbvector<struct iovec>* iov) const {
940 IOBuf const* p = this;
942 // some code can get confused by empty iovs, so skip them
943 if (p->length() > 0) {
944 iov->push_back({(void*)p->data(), folly::to<size_t>(p->length())});
950 size_t IOBuf::fillIov(struct iovec* iov, size_t len) const {
951 IOBuf const* p = this;
954 // some code can get confused by empty iovs, so skip them
955 if (p->length() > 0) {
956 iov[i].iov_base = const_cast<uint8_t*>(p->data());
957 iov[i].iov_len = p->length();
968 size_t IOBufHash::operator()(const IOBuf& buf) const {
969 folly::hash::SpookyHashV2 hasher;
971 io::Cursor cursor(&buf);
973 auto b = cursor.peekBytes();
977 hasher.Update(b.data(), b.size());
978 cursor.skip(b.size());
982 hasher.Final(&h1, &h2);
986 bool IOBufEqual::operator()(const IOBuf& a, const IOBuf& b) const {
990 auto ba = ca.peekBytes();
991 auto bb = cb.peekBytes();
992 if (ba.empty() && bb.empty()) {
994 } else if (ba.empty() || bb.empty()) {
997 size_t n = std::min(ba.size(), bb.size());
999 if (memcmp(ba.data(), bb.data(), n)) {