2 * Copyright 2015 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 FOLLY_IO_IOBUF_H_
18 #define FOLLY_IO_IOBUF_H_
20 #include <glog/logging.h>
29 #include <type_traits>
31 #include <boost/iterator/iterator_facade.hpp>
33 #include <folly/FBString.h>
34 #include <folly/Range.h>
35 #include <folly/FBVector.h>
37 // Ignore shadowing warnings within this file, so includers can use -Wshadow.
38 #pragma GCC diagnostic push
39 #pragma GCC diagnostic ignored "-Wshadow"
44 * An IOBuf is a pointer to a buffer of data.
46 * IOBuf objects are intended to be used primarily for networking code, and are
47 * modelled somewhat after FreeBSD's mbuf data structure, and Linux's sk_buff
50 * IOBuf objects facilitate zero-copy network programming, by allowing multiple
51 * IOBuf objects to point to the same underlying buffer of data, using a
52 * reference count to track when the buffer is no longer needed and can be
59 * The IOBuf itself is a small object containing a pointer to the buffer and
60 * information about which segment of the buffer contains valid data.
62 * The data layout looks like this:
70 * +------------+--------------------+-----------+
71 * | headroom | data | tailroom |
72 * +------------+--------------------+-----------+
74 * buffer() data() tail() bufferEnd()
76 * The length() method returns the length of the valid data; capacity()
77 * returns the entire capacity of the buffer (from buffer() to bufferEnd()).
78 * The headroom() and tailroom() methods return the amount of unused capacity
79 * available before and after the data.
85 * The buffer itself is reference counted, and multiple IOBuf objects may point
86 * to the same buffer. Each IOBuf may point to a different section of valid
87 * data within the underlying buffer. For example, if multiple protocol
88 * requests are read from the network into a single buffer, a separate IOBuf
89 * may be created for each request, all sharing the same underlying buffer.
91 * In other words, when multiple IOBufs share the same underlying buffer, the
92 * data() and tail() methods on each IOBuf may point to a different segment of
93 * the data. However, the buffer() and bufferEnd() methods will point to the
94 * same location for all IOBufs sharing the same underlying buffer.
96 * +-----------+ +---------+
97 * | IOBuf 1 | | IOBuf 2 |
98 * +-----------+ +---------+
100 * data | tail |/ data | tail
102 * +-------------------------------------+
104 * +-------------------------------------+
106 * If you only read data from an IOBuf, you don't need to worry about other
107 * IOBuf objects possibly sharing the same underlying buffer. However, if you
108 * ever write to the buffer you need to first ensure that no other IOBufs point
109 * to the same buffer. The unshare() method may be used to ensure that you
110 * have an unshared buffer.
116 * IOBuf objects also contain pointers to next and previous IOBuf objects.
117 * This can be used to represent a single logical piece of data that its stored
118 * in non-contiguous chunks in separate buffers.
120 * A single IOBuf object can only belong to one chain at a time.
122 * IOBuf chains are always circular. The "prev" pointer in the head of the
123 * chain points to the tail of the chain. However, it is up to the user to
124 * decide which IOBuf is the head. Internally the IOBuf code does not care
125 * which element is the head.
127 * The lifetime of all IOBufs in the chain are linked: when one element in the
128 * chain is deleted, all other chained elements are also deleted. Conceptually
129 * it is simplest to treat this as if the head of the chain owns all other
130 * IOBufs in the chain. When you delete the head of the chain, it will delete
131 * the other elements as well. For this reason, prependChain() and
132 * appendChain() take ownership of of the new elements being added to this
135 * When the coalesce() method is used to coalesce an entire IOBuf chain into a
136 * single IOBuf, all other IOBufs in the chain are eliminated and automatically
137 * deleted. The unshare() method may coalesce the chain; if it does it will
138 * similarly delete all IOBufs eliminated from the chain.
140 * As discussed in the following section, it is up to the user to maintain a
141 * lock around the entire IOBuf chain if multiple threads need to access the
142 * chain. IOBuf does not provide any internal locking.
148 * When used in multithread programs, a single IOBuf object should only be used
149 * in a single thread at a time. If a caller uses a single IOBuf across
150 * multiple threads the caller is responsible for using an external lock to
151 * synchronize access to the IOBuf.
153 * Two separate IOBuf objects may be accessed concurrently in separate threads
154 * without locking, even if they point to the same underlying buffer. The
155 * buffer reference count is always accessed atomically, and no other
156 * operations should affect other IOBufs that point to the same data segment.
157 * The caller is responsible for using unshare() to ensure that the data buffer
158 * is not shared by other IOBufs before writing to it, and this ensures that
159 * the data itself is not modified in one thread while also being accessed from
162 * For IOBuf chains, no two IOBufs in the same chain should be accessed
163 * simultaneously in separate threads. The caller must maintain a lock around
164 * the entire chain if the chain, or individual IOBufs in the chain, may be
165 * accessed by multiple threads.
168 * IOBuf Object Allocation
169 * -----------------------
171 * IOBuf objects themselves exist separately from the data buffer they point
172 * to. Therefore one must also consider how to allocate and manage the IOBuf
175 * It is more common to allocate IOBuf objects on the heap, using the create(),
176 * takeOwnership(), or wrapBuffer() factory functions. The clone()/cloneOne()
177 * functions also return new heap-allocated IOBufs. The createCombined()
178 * function allocates the IOBuf object and data storage space together, in a
179 * single memory allocation. This can improve performance, particularly if you
180 * know that the data buffer and the IOBuf itself will have similar lifetimes.
182 * That said, it is also possible to allocate IOBufs on the stack or inline
183 * inside another object as well. This is useful for cases where the IOBuf is
184 * short-lived, or when the overhead of allocating the IOBuf on the heap is
187 * However, note that stack-allocated IOBufs may only be used as the head of a
188 * chain (or standalone as the only IOBuf in a chain). All non-head members of
189 * an IOBuf chain must be heap allocated. (All functions to add nodes to a
190 * chain require a std::unique_ptr<IOBuf>, which enforces this requrement.)
192 * Copying IOBufs is only meaningful for the head of a chain. The entire chain
193 * is cloned; the IOBufs will become shared, and the old and new IOBufs will
194 * refer to the same underlying memory.
199 * The IOBuf class manages sharing of the underlying buffer that it points to,
200 * maintaining a reference count if multiple IOBufs are pointing at the same
203 * However, it is the callers responsibility to manage sharing and ownership of
204 * IOBuf objects themselves. The IOBuf structure does not provide room for an
205 * intrusive refcount on the IOBuf object itself, only the underlying data
206 * buffer is reference counted. If users want to share the same IOBuf object
207 * between multiple parts of the code, they are responsible for managing this
208 * sharing on their own. (For example, by using a shared_ptr. Alternatively,
209 * users always have the option of using clone() to create a second IOBuf that
210 * points to the same underlying buffer.)
213 // Is T a unique_ptr<> to a standard-layout type?
214 template <class T, class Enable=void> struct IsUniquePtrToSL
215 : public std::false_type { };
216 template <class T, class D>
217 struct IsUniquePtrToSL<
218 std::unique_ptr<T, D>,
219 typename std::enable_if<std::is_standard_layout<T>::value>::type>
220 : public std::true_type { };
221 } // namespace detail
227 enum CreateOp { CREATE };
228 enum WrapBufferOp { WRAP_BUFFER };
229 enum TakeOwnershipOp { TAKE_OWNERSHIP };
230 enum CopyBufferOp { COPY_BUFFER };
232 typedef ByteRange value_type;
233 typedef Iterator iterator;
234 typedef Iterator const_iterator;
236 typedef void (*FreeFunction)(void* buf, void* userData);
239 * Allocate a new IOBuf object with the requested capacity.
241 * Returns a new IOBuf object that must be (eventually) deleted by the
242 * caller. The returned IOBuf may actually have slightly more capacity than
245 * The data pointer will initially point to the start of the newly allocated
246 * buffer, and will have a data length of 0.
248 * Throws std::bad_alloc on error.
250 static std::unique_ptr<IOBuf> create(uint64_t capacity);
251 IOBuf(CreateOp, uint64_t capacity);
254 * Create a new IOBuf, using a single memory allocation to allocate space
255 * for both the IOBuf object and the data storage space.
257 * This saves one memory allocation. However, it can be wasteful if you
258 * later need to grow the buffer using reserve(). If the buffer needs to be
259 * reallocated, the space originally allocated will not be freed() until the
260 * IOBuf object itself is also freed. (It can also be slightly wasteful in
261 * some cases where you clone this IOBuf and then free the original IOBuf.)
263 static std::unique_ptr<IOBuf> createCombined(uint64_t capacity);
266 * Create a new IOBuf, using separate memory allocations for the IOBuf object
267 * for the IOBuf and the data storage space.
269 * This requires two memory allocations, but saves space in the long run
270 * if you know that you will need to reallocate the data buffer later.
272 static std::unique_ptr<IOBuf> createSeparate(uint64_t capacity);
275 * Allocate a new IOBuf chain with the requested total capacity, allocating
276 * no more than maxBufCapacity to each buffer.
278 static std::unique_ptr<IOBuf> createChain(
279 size_t totalCapacity, uint64_t maxBufCapacity);
282 * Create a new IOBuf pointing to an existing data buffer.
284 * The new IOBuffer will assume ownership of the buffer, and free it by
285 * calling the specified FreeFunction when the last IOBuf pointing to this
286 * buffer is destroyed. The function will be called with a pointer to the
287 * buffer as the first argument, and the supplied userData value as the
288 * second argument. The free function must never throw exceptions.
290 * If no FreeFunction is specified, the buffer will be freed using free()
291 * which will result in undefined behavior if the memory was allocated
294 * The IOBuf data pointer will initially point to the start of the buffer,
296 * In the first version of this function, the length of data is unspecified
297 * and is initialized to the capacity of the buffer
299 * In the second version, the user specifies the valid length of data
302 * On error, std::bad_alloc will be thrown. If freeOnError is true (the
303 * default) the buffer will be freed before throwing the error.
305 static std::unique_ptr<IOBuf> takeOwnership(void* buf, uint64_t capacity,
306 FreeFunction freeFn = nullptr,
307 void* userData = nullptr,
308 bool freeOnError = true) {
309 return takeOwnership(buf, capacity, capacity, freeFn,
310 userData, freeOnError);
312 IOBuf(TakeOwnershipOp op, void* buf, uint64_t capacity,
313 FreeFunction freeFn = nullptr, void* userData = nullptr,
314 bool freeOnError = true)
315 : IOBuf(op, buf, capacity, capacity, freeFn, userData, freeOnError) {}
317 static std::unique_ptr<IOBuf> takeOwnership(void* buf, uint64_t capacity,
319 FreeFunction freeFn = nullptr,
320 void* userData = nullptr,
321 bool freeOnError = true);
322 IOBuf(TakeOwnershipOp, void* buf, uint64_t capacity, uint64_t length,
323 FreeFunction freeFn = nullptr, void* userData = nullptr,
324 bool freeOnError = true);
327 * Create a new IOBuf pointing to an existing data buffer made up of
328 * count objects of a given standard-layout type.
330 * This is dangerous -- it is essentially equivalent to doing
331 * reinterpret_cast<unsigned char*> on your data -- but it's often useful
332 * for serialization / deserialization.
334 * The new IOBuffer will assume ownership of the buffer, and free it
335 * appropriately (by calling the UniquePtr's custom deleter, or by calling
336 * delete or delete[] appropriately if there is no custom deleter)
337 * when the buffer is destroyed. The custom deleter, if any, must never
340 * The IOBuf data pointer will initially point to the start of the buffer,
341 * and the length will be the full capacity of the buffer (count *
344 * On error, std::bad_alloc will be thrown, and the buffer will be freed
345 * before throwing the error.
347 template <class UniquePtr>
348 static typename std::enable_if<detail::IsUniquePtrToSL<UniquePtr>::value,
349 std::unique_ptr<IOBuf>>::type
350 takeOwnership(UniquePtr&& buf, size_t count=1);
353 * Create a new IOBuf object that points to an existing user-owned buffer.
355 * This should only be used when the caller knows the lifetime of the IOBuf
356 * object ahead of time and can ensure that all IOBuf objects that will point
357 * to this buffer will be destroyed before the buffer itself is destroyed.
359 * This buffer will not be freed automatically when the last IOBuf
360 * referencing it is destroyed. It is the caller's responsibility to free
361 * the buffer after the last IOBuf has been destroyed.
363 * The IOBuf data pointer will initially point to the start of the buffer,
364 * and the length will be the full capacity of the buffer.
366 * An IOBuf created using wrapBuffer() will always be reported as shared.
367 * unshare() may be used to create a writable copy of the buffer.
369 * On error, std::bad_alloc will be thrown.
371 static std::unique_ptr<IOBuf> wrapBuffer(const void* buf, uint64_t capacity);
372 static std::unique_ptr<IOBuf> wrapBuffer(ByteRange br) {
373 return wrapBuffer(br.data(), br.size());
375 IOBuf(WrapBufferOp op, const void* buf, uint64_t capacity);
376 IOBuf(WrapBufferOp op, ByteRange br);
379 * Convenience function to create a new IOBuf object that copies data from a
380 * user-supplied buffer, optionally allocating a given amount of
381 * headroom and tailroom.
383 static std::unique_ptr<IOBuf> copyBuffer(const void* buf, uint64_t size,
385 uint64_t minTailroom=0);
386 static std::unique_ptr<IOBuf> copyBuffer(ByteRange br,
388 uint64_t minTailroom=0) {
389 return copyBuffer(br.data(), br.size(), headroom, minTailroom);
391 IOBuf(CopyBufferOp op, const void* buf, uint64_t size,
392 uint64_t headroom=0, uint64_t minTailroom=0);
393 IOBuf(CopyBufferOp op, ByteRange br,
394 uint64_t headroom=0, uint64_t minTailroom=0);
397 * Convenience function to create a new IOBuf object that copies data from a
398 * user-supplied string, optionally allocating a given amount of
399 * headroom and tailroom.
401 * Beware when attempting to invoke this function with a constant string
402 * literal and a headroom argument: you will likely end up invoking the
403 * version of copyBuffer() above. IOBuf::copyBuffer("hello", 3) will treat
404 * the first argument as a const void*, and will invoke the version of
405 * copyBuffer() above, with the size argument of 3.
407 static std::unique_ptr<IOBuf> copyBuffer(const std::string& buf,
409 uint64_t minTailroom=0);
410 IOBuf(CopyBufferOp op, const std::string& buf,
411 uint64_t headroom=0, uint64_t minTailroom=0)
412 : IOBuf(op, buf.data(), buf.size(), headroom, minTailroom) {}
415 * A version of copyBuffer() that returns a null pointer if the input string
418 static std::unique_ptr<IOBuf> maybeCopyBuffer(const std::string& buf,
420 uint64_t minTailroom=0);
423 * Convenience function to free a chain of IOBufs held by a unique_ptr.
425 static void destroy(std::unique_ptr<IOBuf>&& data) {
426 auto destroyer = std::move(data);
430 * Destroy this IOBuf.
432 * Deleting an IOBuf will automatically destroy all IOBufs in the chain.
433 * (See the comments above regarding the ownership model of IOBuf chains.
434 * All subsequent IOBufs in the chain are considered to be owned by the head
435 * of the chain. Users should only explicitly delete the head of a chain.)
437 * When each individual IOBuf is destroyed, it will release its reference
438 * count on the underlying buffer. If it was the last user of the buffer,
439 * the buffer will be freed.
444 * Check whether the chain is empty (i.e., whether the IOBufs in the
445 * chain have a total data length of zero).
447 * This method is semantically equivalent to
448 * i->computeChainDataLength()==0
449 * but may run faster because it can short-circuit as soon as it
450 * encounters a buffer with length()!=0
455 * Get the pointer to the start of the data.
457 const uint8_t* data() const {
462 * Get a writable pointer to the start of the data.
464 * The caller is responsible for calling unshare() first to ensure that it is
465 * actually safe to write to the buffer.
467 uint8_t* writableData() {
472 * Get the pointer to the end of the data.
474 const uint8_t* tail() const {
475 return data_ + length_;
479 * Get a writable pointer to the end of the data.
481 * The caller is responsible for calling unshare() first to ensure that it is
482 * actually safe to write to the buffer.
484 uint8_t* writableTail() {
485 return data_ + length_;
489 * Get the data length.
491 uint64_t length() const {
496 * Get the amount of head room.
498 * Returns the number of bytes in the buffer before the start of the data.
500 uint64_t headroom() const {
501 return data_ - buffer();
505 * Get the amount of tail room.
507 * Returns the number of bytes in the buffer after the end of the data.
509 uint64_t tailroom() const {
510 return bufferEnd() - tail();
514 * Get the pointer to the start of the buffer.
516 * Note that this is the pointer to the very beginning of the usable buffer,
517 * not the start of valid data within the buffer. Use the data() method to
518 * get a pointer to the start of the data within the buffer.
520 const uint8_t* buffer() const {
525 * Get a writable pointer to the start of the buffer.
527 * The caller is responsible for calling unshare() first to ensure that it is
528 * actually safe to write to the buffer.
530 uint8_t* writableBuffer() {
535 * Get the pointer to the end of the buffer.
537 * Note that this is the pointer to the very end of the usable buffer,
538 * not the end of valid data within the buffer. Use the tail() method to
539 * get a pointer to the end of the data within the buffer.
541 const uint8_t* bufferEnd() const {
542 return buf_ + capacity_;
546 * Get the total size of the buffer.
548 * This returns the total usable length of the buffer. Use the length()
549 * method to get the length of the actual valid data in this IOBuf.
551 uint64_t capacity() const {
556 * Get a pointer to the next IOBuf in this chain.
561 const IOBuf* next() const {
566 * Get a pointer to the previous IOBuf in this chain.
571 const IOBuf* prev() const {
576 * Shift the data forwards in the buffer.
578 * This shifts the data pointer forwards in the buffer to increase the
579 * headroom. This is commonly used to increase the headroom in a newly
582 * The caller is responsible for ensuring that there is sufficient
583 * tailroom in the buffer before calling advance().
585 * If there is a non-zero data length, advance() will use memmove() to shift
586 * the data forwards in the buffer. In this case, the caller is responsible
587 * for making sure the buffer is unshared, so it will not affect other IOBufs
588 * that may be sharing the same underlying buffer.
590 void advance(uint64_t amount) {
591 // In debug builds, assert if there is a problem.
592 assert(amount <= tailroom());
595 memmove(data_ + amount, data_, length_);
601 * Shift the data backwards in the buffer.
603 * The caller is responsible for ensuring that there is sufficient headroom
604 * in the buffer before calling retreat().
606 * If there is a non-zero data length, retreat() will use memmove() to shift
607 * the data backwards in the buffer. In this case, the caller is responsible
608 * for making sure the buffer is unshared, so it will not affect other IOBufs
609 * that may be sharing the same underlying buffer.
611 void retreat(uint64_t amount) {
612 // In debug builds, assert if there is a problem.
613 assert(amount <= headroom());
616 memmove(data_ - amount, data_, length_);
622 * Adjust the data pointer to include more valid data at the beginning.
624 * This moves the data pointer backwards to include more of the available
625 * buffer. The caller is responsible for ensuring that there is sufficient
626 * headroom for the new data. The caller is also responsible for populating
627 * this section with valid data.
629 * This does not modify any actual data in the buffer.
631 void prepend(uint64_t amount) {
632 DCHECK_LE(amount, headroom());
638 * Adjust the tail pointer to include more valid data at the end.
640 * This moves the tail pointer forwards to include more of the available
641 * buffer. The caller is responsible for ensuring that there is sufficient
642 * tailroom for the new data. The caller is also responsible for populating
643 * this section with valid data.
645 * This does not modify any actual data in the buffer.
647 void append(uint64_t amount) {
648 DCHECK_LE(amount, tailroom());
653 * Adjust the data pointer forwards to include less valid data.
655 * This moves the data pointer forwards so that the first amount bytes are no
656 * longer considered valid data. The caller is responsible for ensuring that
657 * amount is less than or equal to the actual data length.
659 * This does not modify any actual data in the buffer.
661 void trimStart(uint64_t amount) {
662 DCHECK_LE(amount, length_);
668 * Adjust the tail pointer backwards to include less valid data.
670 * This moves the tail pointer backwards so that the last amount bytes are no
671 * longer considered valid data. The caller is responsible for ensuring that
672 * amount is less than or equal to the actual data length.
674 * This does not modify any actual data in the buffer.
676 void trimEnd(uint64_t amount) {
677 DCHECK_LE(amount, length_);
684 * Postcondition: headroom() == 0, length() == 0, tailroom() == capacity()
687 data_ = writableBuffer();
692 * Ensure that this buffer has at least minHeadroom headroom bytes and at
693 * least minTailroom tailroom bytes. The buffer must be writable
694 * (you must call unshare() before this, if necessary).
696 * Postcondition: headroom() >= minHeadroom, tailroom() >= minTailroom,
697 * the data (between data() and data() + length()) is preserved.
699 void reserve(uint64_t minHeadroom, uint64_t minTailroom) {
700 // Maybe we don't need to do anything.
701 if (headroom() >= minHeadroom && tailroom() >= minTailroom) {
704 // If the buffer is empty but we have enough total room (head + tail),
705 // move the data_ pointer around.
707 headroom() + tailroom() >= minHeadroom + minTailroom) {
708 data_ = writableBuffer() + minHeadroom;
711 // Bah, we have to do actual work.
712 reserveSlow(minHeadroom, minTailroom);
716 * Return true if this IOBuf is part of a chain of multiple IOBufs, or false
717 * if this is the only IOBuf in its chain.
719 bool isChained() const {
720 assert((next_ == this) == (prev_ == this));
721 return next_ != this;
725 * Get the number of IOBufs in this chain.
727 * Beware that this method has to walk the entire chain.
728 * Use isChained() if you just want to check if this IOBuf is part of a chain
731 size_t countChainElements() const;
734 * Get the length of all the data in this IOBuf chain.
736 * Beware that this method has to walk the entire chain.
738 uint64_t computeChainDataLength() const;
741 * Insert another IOBuf chain immediately before this IOBuf.
743 * For example, if there are two IOBuf chains (A, B, C) and (D, E, F),
744 * and B->prependChain(D) is called, the (D, E, F) chain will be subsumed
745 * and become part of the chain starting at A, which will now look like
748 * Note that since IOBuf chains are circular, head->prependChain(other) can
749 * be used to append the other chain at the very end of the chain pointed to
750 * by head. For example, if there are two IOBuf chains (A, B, C) and
751 * (D, E, F), and A->prependChain(D) is called, the chain starting at A will
752 * now consist of (A, B, C, D, E, F)
754 * The elements in the specified IOBuf chain will become part of this chain,
755 * and will be owned by the head of this chain. When this chain is
756 * destroyed, all elements in the supplied chain will also be destroyed.
758 * For this reason, appendChain() only accepts an rvalue-reference to a
759 * unique_ptr(), to make it clear that it is taking ownership of the supplied
760 * chain. If you have a raw pointer, you can pass in a new temporary
761 * unique_ptr around the raw pointer. If you have an existing,
762 * non-temporary unique_ptr, you must call std::move(ptr) to make it clear
763 * that you are destroying the original pointer.
765 void prependChain(std::unique_ptr<IOBuf>&& iobuf);
768 * Append another IOBuf chain immediately after this IOBuf.
770 * For example, if there are two IOBuf chains (A, B, C) and (D, E, F),
771 * and B->appendChain(D) is called, the (D, E, F) chain will be subsumed
772 * and become part of the chain starting at A, which will now look like
775 * The elements in the specified IOBuf chain will become part of this chain,
776 * and will be owned by the head of this chain. When this chain is
777 * destroyed, all elements in the supplied chain will also be destroyed.
779 * For this reason, appendChain() only accepts an rvalue-reference to a
780 * unique_ptr(), to make it clear that it is taking ownership of the supplied
781 * chain. If you have a raw pointer, you can pass in a new temporary
782 * unique_ptr around the raw pointer. If you have an existing,
783 * non-temporary unique_ptr, you must call std::move(ptr) to make it clear
784 * that you are destroying the original pointer.
786 void appendChain(std::unique_ptr<IOBuf>&& iobuf) {
787 // Just use prependChain() on the next element in our chain
788 next_->prependChain(std::move(iobuf));
792 * Remove this IOBuf from its current chain.
794 * Since ownership of all elements an IOBuf chain is normally maintained by
795 * the head of the chain, unlink() transfers ownership of this IOBuf from the
796 * chain and gives it to the caller. A new unique_ptr to the IOBuf is
797 * returned to the caller. The caller must store the returned unique_ptr (or
798 * call release() on it) to take ownership, otherwise the IOBuf will be
799 * immediately destroyed.
801 * Since unlink transfers ownership of the IOBuf to the caller, be careful
802 * not to call unlink() on the head of a chain if you already maintain
803 * ownership on the head of the chain via other means. The pop() method
804 * is a better choice for that situation.
806 std::unique_ptr<IOBuf> unlink() {
807 next_->prev_ = prev_;
808 prev_->next_ = next_;
811 return std::unique_ptr<IOBuf>(this);
815 * Remove this IOBuf from its current chain and return a unique_ptr to
816 * the IOBuf that formerly followed it in the chain.
818 std::unique_ptr<IOBuf> pop() {
820 next_->prev_ = prev_;
821 prev_->next_ = next_;
824 return std::unique_ptr<IOBuf>((next == this) ? nullptr : next);
828 * Remove a subchain from this chain.
830 * Remove the subchain starting at head and ending at tail from this chain.
832 * Returns a unique_ptr pointing to head. (In other words, ownership of the
833 * head of the subchain is transferred to the caller.) If the caller ignores
834 * the return value and lets the unique_ptr be destroyed, the subchain will
835 * be immediately destroyed.
837 * The subchain referenced by the specified head and tail must be part of the
838 * same chain as the current IOBuf, but must not contain the current IOBuf.
839 * However, the specified head and tail may be equal to each other (i.e.,
840 * they may be a subchain of length 1).
842 std::unique_ptr<IOBuf> separateChain(IOBuf* head, IOBuf* tail) {
843 assert(head != this);
844 assert(tail != this);
846 head->prev_->next_ = tail->next_;
847 tail->next_->prev_ = head->prev_;
852 return std::unique_ptr<IOBuf>(head);
856 * Return true if at least one of the IOBufs in this chain are shared,
857 * or false if all of the IOBufs point to unique buffers.
859 * Use isSharedOne() to only check this IOBuf rather than the entire chain.
861 bool isShared() const {
862 const IOBuf* current = this;
864 if (current->isSharedOne()) {
867 current = current->next_;
868 if (current == this) {
875 * Return true if all IOBufs in this chain are managed by the usual
876 * refcounting mechanism (and so the lifetime of the underlying memory
877 * can be extended by clone()).
879 bool isManaged() const {
880 const IOBuf* current = this;
882 if (!current->isManagedOne()) {
885 current = current->next_;
886 if (current == this) {
893 * Return true if this IOBuf is managed by the usual refcounting mechanism
894 * (and so the lifetime of the underlying memory can be extended by
897 bool isManagedOne() const {
902 * Return true if other IOBufs are also pointing to the buffer used by this
903 * IOBuf, and false otherwise.
905 * If this IOBuf points at a buffer owned by another (non-IOBuf) part of the
906 * code (i.e., if the IOBuf was created using wrapBuffer(), or was cloned
907 * from such an IOBuf), it is always considered shared.
909 * This only checks the current IOBuf, and not other IOBufs in the chain.
911 bool isSharedOne() const {
912 // If this is a user-owned buffer, it is always considered shared
913 if (UNLIKELY(!sharedInfo())) {
917 if (LIKELY(!(flags() & kFlagMaybeShared))) {
921 // kFlagMaybeShared is set, so we need to check the reference count.
922 // (Checking the reference count requires an atomic operation, which is why
923 // we prefer to only check kFlagMaybeShared if possible.)
924 bool shared = sharedInfo()->refcount.load(std::memory_order_acquire) > 1;
926 // we're the last one left
927 clearFlags(kFlagMaybeShared);
933 * Ensure that this IOBuf has a unique buffer that is not shared by other
936 * unshare() operates on an entire chain of IOBuf objects. If the chain is
937 * shared, it may also coalesce the chain when making it unique. If the
938 * chain is coalesced, subsequent IOBuf objects in the current chain will be
939 * automatically deleted.
941 * Note that buffers owned by other (non-IOBuf) users are automatically
944 * Throws std::bad_alloc on error. On error the IOBuf chain will be
947 * Currently unshare may also throw std::overflow_error if it tries to
948 * coalesce. (TODO: In the future it would be nice if unshare() were smart
949 * enough not to coalesce the entire buffer if the data is too large.
950 * However, in practice this seems unlikely to become an issue.)
961 * Ensure that this IOBuf has a unique buffer that is not shared by other
964 * unshareOne() operates on a single IOBuf object. This IOBuf will have a
965 * unique buffer after unshareOne() returns, but other IOBufs in the chain
966 * may still be shared after unshareOne() returns.
968 * Throws std::bad_alloc on error. On error the IOBuf will be unmodified.
977 * Ensure that the memory that IOBufs in this chain refer to will continue to
978 * be allocated for as long as the IOBufs of the chain (or any clone()s
979 * created from this point onwards) is alive.
981 * This only has an effect for user-owned buffers (created with the
982 * WRAP_BUFFER constructor or wrapBuffer factory function), in which case
983 * those buffers are unshared.
987 makeManagedChained();
994 * Ensure that the memory that this IOBuf refers to will continue to be
995 * allocated for as long as this IOBuf (or any clone()s created from this
996 * point onwards) is alive.
998 * This only has an effect for user-owned buffers (created with the
999 * WRAP_BUFFER constructor or wrapBuffer factory function), in which case
1000 * those buffers are unshared.
1002 void makeManagedOne() {
1003 if (!isManagedOne()) {
1004 // We can call the internal function directly; unmanaged implies shared.
1010 * Coalesce this IOBuf chain into a single buffer.
1012 * This method moves all of the data in this IOBuf chain into a single
1013 * contiguous buffer, if it is not already in one buffer. After coalesce()
1014 * returns, this IOBuf will be a chain of length one. Other IOBufs in the
1015 * chain will be automatically deleted.
1017 * After coalescing, the IOBuf will have at least as much headroom as the
1018 * first IOBuf in the chain, and at least as much tailroom as the last IOBuf
1021 * Throws std::bad_alloc on error. On error the IOBuf chain will be
1024 * Returns ByteRange that points to the data IOBuf stores.
1026 ByteRange coalesce() {
1030 return ByteRange(data_, length_);
1034 * Ensure that this chain has at least maxLength bytes available as a
1035 * contiguous memory range.
1037 * This method coalesces whole buffers in the chain into this buffer as
1038 * necessary until this buffer's length() is at least maxLength.
1040 * After coalescing, the IOBuf will have at least as much headroom as the
1041 * first IOBuf in the chain, and at least as much tailroom as the last IOBuf
1042 * that was coalesced.
1044 * Throws std::bad_alloc or std::overflow_error on error. On error the IOBuf
1045 * chain will be unmodified. Throws std::overflow_error if maxLength is
1046 * longer than the total chain length.
1048 * Upon return, either enough of the chain was coalesced into a contiguous
1049 * region, or the entire chain was coalesced. That is,
1050 * length() >= maxLength || !isChained() is true.
1052 void gather(uint64_t maxLength) {
1053 if (!isChained() || length_ >= maxLength) {
1056 coalesceSlow(maxLength);
1060 * Return a new IOBuf chain sharing the same data as this chain.
1062 * The new IOBuf chain will normally point to the same underlying data
1063 * buffers as the original chain. (The one exception to this is if some of
1064 * the IOBufs in this chain contain small internal data buffers which cannot
1067 std::unique_ptr<IOBuf> clone() const;
1070 * Return a new IOBuf with the same data as this IOBuf.
1072 * The new IOBuf returned will not be part of a chain (even if this IOBuf is
1073 * part of a larger chain).
1075 std::unique_ptr<IOBuf> cloneOne() const;
1078 * Similar to Clone(). But use other as the head node. Other nodes in the
1079 * chain (if any) will be allocted on heap.
1081 void cloneInto(IOBuf& other) const;
1084 * Similar to CloneOne(). But to fill an existing IOBuf instead of a new
1087 void cloneOneInto(IOBuf& other) const;
1090 * Return an iovector suitable for e.g. writev()
1092 * auto iov = buf->getIov();
1093 * auto xfer = writev(fd, iov.data(), iov.size());
1095 * Naturally, the returned iovector is invalid if you modify the buffer
1098 folly::fbvector<struct iovec> getIov() const;
1101 * Update an existing iovec array with the IOBuf data.
1103 * New iovecs will be appended to the existing vector; anything already
1104 * present in the vector will be left unchanged.
1106 * Naturally, the returned iovec data will be invalid if you modify the
1109 void appendToIov(folly::fbvector<struct iovec>* iov) const;
1112 * Fill an iovec array with the IOBuf data.
1114 * Returns the number of iovec filled. If there are more buffer than
1115 * iovec, returns 0. This version is suitable to use with stack iovec
1118 * Naturally, the filled iovec data will be invalid if you modify the
1121 size_t fillIov(struct iovec* iov, size_t len) const;
1124 * Overridden operator new and delete.
1125 * These perform specialized memory management to help support
1126 * createCombined(), which allocates IOBuf objects together with the buffer
1129 void* operator new(size_t size);
1130 void* operator new(size_t size, void* ptr);
1131 void operator delete(void* ptr);
1134 * Destructively convert this IOBuf to a fbstring efficiently.
1135 * We rely on fbstring's AcquireMallocatedString constructor to
1138 fbstring moveToFbString();
1141 * Iteration support: a chain of IOBufs may be iterated through using
1142 * STL-style iterators over const ByteRanges. Iterators are only invalidated
1143 * if the IOBuf that they currently point to is removed.
1145 Iterator cbegin() const;
1146 Iterator cend() const;
1147 Iterator begin() const;
1148 Iterator end() const;
1151 * Allocate a new null buffer.
1153 * This can be used to allocate an empty IOBuf on the stack. It will have no
1154 * space allocated for it. This is generally useful only to later use move
1155 * assignment to fill out the IOBuf.
1160 * Move constructor and assignment operator.
1162 * In general, you should only ever move the head of an IOBuf chain.
1163 * Internal nodes in an IOBuf chain are owned by the head of the chain, and
1164 * should not be moved from. (Technically, nothing prevents you from moving
1165 * a non-head node, but the moved-to node will replace the moved-from node in
1166 * the chain. This has implications for ownership, since non-head nodes are
1167 * owned by the chain head. You are then responsible for relinquishing
1168 * ownership of the moved-to node, and manually deleting the moved-from
1171 * With the move assignment operator, the destination of the move should be
1172 * the head of an IOBuf chain or a solitary IOBuf not part of a chain. If
1173 * the move destination is part of a chain, all other IOBufs in the chain
1176 IOBuf(IOBuf&& other) noexcept;
1177 IOBuf& operator=(IOBuf&& other) noexcept;
1179 IOBuf(const IOBuf& other);
1180 IOBuf& operator=(const IOBuf& other);
1183 enum FlagsEnum : uintptr_t {
1184 // Adding any more flags would not work on 32-bit architectures,
1185 // as these flags are stashed in the least significant 2 bits of a
1186 // max-align-aligned pointer.
1187 kFlagFreeSharedInfo = 0x1,
1188 kFlagMaybeShared = 0x2,
1189 kFlagMask = kFlagFreeSharedInfo | kFlagMaybeShared
1194 SharedInfo(FreeFunction fn, void* arg);
1196 // A pointer to a function to call to free the buffer when the refcount
1197 // hits 0. If this is null, free() will be used instead.
1198 FreeFunction freeFn;
1200 std::atomic<uint32_t> refcount;
1202 // Helper structs for use by operator new and delete
1205 struct HeapFullStorage;
1208 * Create a new IOBuf pointing to an external buffer.
1210 * The caller is responsible for holding a reference count for this new
1211 * IOBuf. The IOBuf constructor does not automatically increment the
1214 struct InternalConstructor {}; // avoid conflicts
1215 IOBuf(InternalConstructor, uintptr_t flagsAndSharedInfo,
1216 uint8_t* buf, uint64_t capacity,
1217 uint8_t* data, uint64_t length);
1219 void unshareOneSlow();
1220 void unshareChained();
1221 void makeManagedChained();
1222 void coalesceSlow();
1223 void coalesceSlow(size_t maxLength);
1224 // newLength must be the entire length of the buffers between this and
1225 // end (no truncation)
1226 void coalesceAndReallocate(
1230 size_t newTailroom);
1231 void coalesceAndReallocate(size_t newLength, IOBuf* end) {
1232 coalesceAndReallocate(headroom(), newLength, end, end->prev_->tailroom());
1234 void decrementRefcount();
1235 void reserveSlow(uint64_t minHeadroom, uint64_t minTailroom);
1236 void freeExtBuffer();
1238 static size_t goodExtBufferSize(uint64_t minCapacity);
1239 static void initExtBuffer(uint8_t* buf, size_t mallocSize,
1240 SharedInfo** infoReturn,
1241 uint64_t* capacityReturn);
1242 static void allocExtBuffer(uint64_t minCapacity,
1243 uint8_t** bufReturn,
1244 SharedInfo** infoReturn,
1245 uint64_t* capacityReturn);
1246 static void releaseStorage(HeapStorage* storage, uint16_t freeFlags);
1247 static void freeInternalBuf(void* buf, void* userData);
1254 * Links to the next and the previous IOBuf in this chain.
1256 * The chain is circularly linked (the last element in the chain points back
1257 * at the head), and next_ and prev_ can never be null. If this IOBuf is the
1258 * only element in the chain, next_ and prev_ will both point to this.
1264 * A pointer to the start of the data referenced by this IOBuf, and the
1265 * length of the data.
1267 * This may refer to any subsection of the actual buffer capacity.
1269 uint8_t* data_{nullptr};
1270 uint8_t* buf_{nullptr};
1271 uint64_t length_{0};
1272 uint64_t capacity_{0};
1274 // Pack flags in least significant 2 bits, sharedInfo in the rest
1275 mutable uintptr_t flagsAndSharedInfo_{0};
1277 static inline uintptr_t packFlagsAndSharedInfo(uintptr_t flags,
1279 uintptr_t uinfo = reinterpret_cast<uintptr_t>(info);
1280 DCHECK_EQ(flags & ~kFlagMask, 0);
1281 DCHECK_EQ(uinfo & kFlagMask, 0);
1282 return flags | uinfo;
1285 inline SharedInfo* sharedInfo() const {
1286 return reinterpret_cast<SharedInfo*>(flagsAndSharedInfo_ & ~kFlagMask);
1289 inline void setSharedInfo(SharedInfo* info) {
1290 uintptr_t uinfo = reinterpret_cast<uintptr_t>(info);
1291 DCHECK_EQ(uinfo & kFlagMask, 0);
1292 flagsAndSharedInfo_ = (flagsAndSharedInfo_ & kFlagMask) | uinfo;
1295 inline uintptr_t flags() const {
1296 return flagsAndSharedInfo_ & kFlagMask;
1299 // flags_ are changed from const methods
1300 inline void setFlags(uintptr_t flags) const {
1301 DCHECK_EQ(flags & ~kFlagMask, 0);
1302 flagsAndSharedInfo_ |= flags;
1305 inline void clearFlags(uintptr_t flags) const {
1306 DCHECK_EQ(flags & ~kFlagMask, 0);
1307 flagsAndSharedInfo_ &= ~flags;
1310 inline void setFlagsAndSharedInfo(uintptr_t flags, SharedInfo* info) {
1311 flagsAndSharedInfo_ = packFlagsAndSharedInfo(flags, info);
1314 struct DeleterBase {
1315 virtual ~DeleterBase() { }
1316 virtual void dispose(void* p) = 0;
1319 template <class UniquePtr>
1320 struct UniquePtrDeleter : public DeleterBase {
1321 typedef typename UniquePtr::pointer Pointer;
1322 typedef typename UniquePtr::deleter_type Deleter;
1324 explicit UniquePtrDeleter(Deleter deleter) : deleter_(std::move(deleter)){ }
1325 void dispose(void* p) {
1327 deleter_(static_cast<Pointer>(p));
1338 static void freeUniquePtrBuffer(void* ptr, void* userData) {
1339 static_cast<DeleterBase*>(userData)->dispose(ptr);
1344 * Hasher for IOBuf objects. Hashes the entire chain using SpookyHashV2.
1347 size_t operator()(const IOBuf& buf) const;
1348 size_t operator()(const std::unique_ptr<IOBuf>& buf) const {
1349 return buf ? (*this)(*buf) : 0;
1354 * Equality predicate for IOBuf objects. Compares data in the entire chain.
1357 bool operator()(const IOBuf& a, const IOBuf& b) const;
1358 bool operator()(const std::unique_ptr<IOBuf>& a,
1359 const std::unique_ptr<IOBuf>& b) const {
1362 } else if (!a || !b) {
1365 return (*this)(*a, *b);
1370 template <class UniquePtr>
1371 typename std::enable_if<detail::IsUniquePtrToSL<UniquePtr>::value,
1372 std::unique_ptr<IOBuf>>::type
1373 IOBuf::takeOwnership(UniquePtr&& buf, size_t count) {
1374 size_t size = count * sizeof(typename UniquePtr::element_type);
1375 auto deleter = new UniquePtrDeleter<UniquePtr>(buf.get_deleter());
1376 return takeOwnership(buf.release(),
1378 &IOBuf::freeUniquePtrBuffer,
1382 inline std::unique_ptr<IOBuf> IOBuf::copyBuffer(
1383 const void* data, uint64_t size, uint64_t headroom,
1384 uint64_t minTailroom) {
1385 uint64_t capacity = headroom + size + minTailroom;
1386 std::unique_ptr<IOBuf> buf = create(capacity);
1387 buf->advance(headroom);
1388 memcpy(buf->writableData(), data, size);
1393 inline std::unique_ptr<IOBuf> IOBuf::copyBuffer(const std::string& buf,
1395 uint64_t minTailroom) {
1396 return copyBuffer(buf.data(), buf.size(), headroom, minTailroom);
1399 inline std::unique_ptr<IOBuf> IOBuf::maybeCopyBuffer(const std::string& buf,
1401 uint64_t minTailroom) {
1405 return copyBuffer(buf.data(), buf.size(), headroom, minTailroom);
1408 class IOBuf::Iterator : public boost::iterator_facade<
1409 IOBuf::Iterator, // Derived
1410 const ByteRange, // Value
1411 boost::forward_traversal_tag // Category or traversal
1413 friend class boost::iterator_core_access;
1415 // Note that IOBufs are stored as a circular list without a guard node,
1416 // so pos == end is ambiguous (it may mean "begin" or "end"). To solve
1417 // the ambiguity (at the cost of one extra comparison in the "increment"
1418 // code path), we define end iterators as having pos_ == end_ == nullptr
1419 // and we only allow forward iteration.
1420 explicit Iterator(const IOBuf* pos, const IOBuf* end)
1423 // Sadly, we must return by const reference, not by value.
1431 val_ = ByteRange(pos_->data(), pos_->tail());
1434 void adjustForEnd() {
1436 pos_ = end_ = nullptr;
1443 const ByteRange& dereference() const {
1447 bool equal(const Iterator& other) const {
1448 // We must compare end_ in addition to pos_, because forward traversal
1449 // requires that if two iterators are equal (a == b) and dereferenceable,
1451 return pos_ == other.pos_ && end_ == other.end_;
1455 pos_ = pos_->next();
1464 inline IOBuf::Iterator IOBuf::begin() const { return cbegin(); }
1465 inline IOBuf::Iterator IOBuf::end() const { return cend(); }
1469 #pragma GCC diagnostic pop
1471 #endif // FOLLY_IO_IOBUF_H_