2 * Copyright 2014 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 * Additionally, no copy-constructor or assignment operator currently exists,
193 * so stack-allocated IOBufs may only be moved, not copied. (Technically
194 * nothing is preventing us from adding a copy constructor and assignment
195 * operator. However, it seems like this would add the possibility for some
196 * confusion. We would need to determine if these functions would copy just a
197 * single buffer, or the entire chain.)
203 * The IOBuf class manages sharing of the underlying buffer that it points to,
204 * maintaining a reference count if multiple IOBufs are pointing at the same
207 * However, it is the callers responsibility to manage sharing and ownership of
208 * IOBuf objects themselves. The IOBuf structure does not provide room for an
209 * intrusive refcount on the IOBuf object itself, only the underlying data
210 * buffer is reference counted. If users want to share the same IOBuf object
211 * between multiple parts of the code, they are responsible for managing this
212 * sharing on their own. (For example, by using a shared_ptr. Alternatively,
213 * users always have the option of using clone() to create a second IOBuf that
214 * points to the same underlying buffer.)
217 // Is T a unique_ptr<> to a standard-layout type?
218 template <class T, class Enable=void> struct IsUniquePtrToSL
219 : public std::false_type { };
220 template <class T, class D>
221 struct IsUniquePtrToSL<
222 std::unique_ptr<T, D>,
223 typename std::enable_if<std::is_standard_layout<T>::value>::type>
224 : public std::true_type { };
225 } // namespace detail
231 enum CreateOp { CREATE };
232 enum WrapBufferOp { WRAP_BUFFER };
233 enum TakeOwnershipOp { TAKE_OWNERSHIP };
234 enum CopyBufferOp { COPY_BUFFER };
236 typedef ByteRange value_type;
237 typedef Iterator iterator;
238 typedef Iterator const_iterator;
240 typedef void (*FreeFunction)(void* buf, void* userData);
243 * Allocate a new IOBuf object with the requested capacity.
245 * Returns a new IOBuf object that must be (eventually) deleted by the
246 * caller. The returned IOBuf may actually have slightly more capacity than
249 * The data pointer will initially point to the start of the newly allocated
250 * buffer, and will have a data length of 0.
252 * Throws std::bad_alloc on error.
254 static std::unique_ptr<IOBuf> create(uint64_t capacity);
255 IOBuf(CreateOp, uint64_t capacity);
258 * Create a new IOBuf, using a single memory allocation to allocate space
259 * for both the IOBuf object and the data storage space.
261 * This saves one memory allocation. However, it can be wasteful if you
262 * later need to grow the buffer using reserve(). If the buffer needs to be
263 * reallocated, the space originally allocated will not be freed() until the
264 * IOBuf object itself is also freed. (It can also be slightly wasteful in
265 * some cases where you clone this IOBuf and then free the original IOBuf.)
267 static std::unique_ptr<IOBuf> createCombined(uint64_t capacity);
270 * Create a new IOBuf, using separate memory allocations for the IOBuf object
271 * for the IOBuf and the data storage space.
273 * This requires two memory allocations, but saves space in the long run
274 * if you know that you will need to reallocate the data buffer later.
276 static std::unique_ptr<IOBuf> createSeparate(uint64_t capacity);
279 * Allocate a new IOBuf chain with the requested total capacity, allocating
280 * no more than maxBufCapacity to each buffer.
282 static std::unique_ptr<IOBuf> createChain(
283 size_t totalCapacity, uint64_t maxBufCapacity);
286 * Create a new IOBuf pointing to an existing data buffer.
288 * The new IOBuffer will assume ownership of the buffer, and free it by
289 * calling the specified FreeFunction when the last IOBuf pointing to this
290 * buffer is destroyed. The function will be called with a pointer to the
291 * buffer as the first argument, and the supplied userData value as the
292 * second argument. The free function must never throw exceptions.
294 * If no FreeFunction is specified, the buffer will be freed using free()
295 * which will result in undefined behavior if the memory was allocated
298 * The IOBuf data pointer will initially point to the start of the buffer,
300 * In the first version of this function, the length of data is unspecified
301 * and is initialized to the capacity of the buffer
303 * In the second version, the user specifies the valid length of data
306 * On error, std::bad_alloc will be thrown. If freeOnError is true (the
307 * default) the buffer will be freed before throwing the error.
309 static std::unique_ptr<IOBuf> takeOwnership(void* buf, uint64_t capacity,
310 FreeFunction freeFn = nullptr,
311 void* userData = nullptr,
312 bool freeOnError = true) {
313 return takeOwnership(buf, capacity, capacity, freeFn,
314 userData, freeOnError);
316 IOBuf(TakeOwnershipOp op, void* buf, uint64_t capacity,
317 FreeFunction freeFn = nullptr, void* userData = nullptr,
318 bool freeOnError = true)
319 : IOBuf(op, buf, capacity, capacity, freeFn, userData, freeOnError) {}
321 static std::unique_ptr<IOBuf> takeOwnership(void* buf, uint64_t capacity,
323 FreeFunction freeFn = nullptr,
324 void* userData = nullptr,
325 bool freeOnError = true);
326 IOBuf(TakeOwnershipOp, void* buf, uint64_t capacity, uint64_t length,
327 FreeFunction freeFn = nullptr, void* userData = nullptr,
328 bool freeOnError = true);
331 * Create a new IOBuf pointing to an existing data buffer made up of
332 * count objects of a given standard-layout type.
334 * This is dangerous -- it is essentially equivalent to doing
335 * reinterpret_cast<unsigned char*> on your data -- but it's often useful
336 * for serialization / deserialization.
338 * The new IOBuffer will assume ownership of the buffer, and free it
339 * appropriately (by calling the UniquePtr's custom deleter, or by calling
340 * delete or delete[] appropriately if there is no custom deleter)
341 * when the buffer is destroyed. The custom deleter, if any, must never
344 * The IOBuf data pointer will initially point to the start of the buffer,
345 * and the length will be the full capacity of the buffer (count *
348 * On error, std::bad_alloc will be thrown, and the buffer will be freed
349 * before throwing the error.
351 template <class UniquePtr>
352 static typename std::enable_if<detail::IsUniquePtrToSL<UniquePtr>::value,
353 std::unique_ptr<IOBuf>>::type
354 takeOwnership(UniquePtr&& buf, size_t count=1);
357 * Create a new IOBuf object that points to an existing user-owned buffer.
359 * This should only be used when the caller knows the lifetime of the IOBuf
360 * object ahead of time and can ensure that all IOBuf objects that will point
361 * to this buffer will be destroyed before the buffer itself is destroyed.
363 * This buffer will not be freed automatically when the last IOBuf
364 * referencing it is destroyed. It is the caller's responsibility to free
365 * the buffer after the last IOBuf has been destroyed.
367 * The IOBuf data pointer will initially point to the start of the buffer,
368 * and the length will be the full capacity of the buffer.
370 * An IOBuf created using wrapBuffer() will always be reported as shared.
371 * unshare() may be used to create a writable copy of the buffer.
373 * On error, std::bad_alloc will be thrown.
375 static std::unique_ptr<IOBuf> wrapBuffer(const void* buf, uint64_t capacity);
376 static std::unique_ptr<IOBuf> wrapBuffer(ByteRange br) {
377 return wrapBuffer(br.data(), br.size());
379 IOBuf(WrapBufferOp op, const void* buf, uint64_t capacity);
380 IOBuf(WrapBufferOp op, ByteRange br);
383 * Convenience function to create a new IOBuf object that copies data from a
384 * user-supplied buffer, optionally allocating a given amount of
385 * headroom and tailroom.
387 static std::unique_ptr<IOBuf> copyBuffer(const void* buf, uint64_t size,
389 uint64_t minTailroom=0);
390 static std::unique_ptr<IOBuf> copyBuffer(ByteRange br,
392 uint64_t minTailroom=0) {
393 return copyBuffer(br.data(), br.size(), headroom, minTailroom);
395 IOBuf(CopyBufferOp op, const void* buf, uint64_t size,
396 uint64_t headroom=0, uint64_t minTailroom=0);
397 IOBuf(CopyBufferOp op, ByteRange br,
398 uint64_t headroom=0, uint64_t minTailroom=0);
401 * Convenience function to create a new IOBuf object that copies data from a
402 * user-supplied string, optionally allocating a given amount of
403 * headroom and tailroom.
405 * Beware when attempting to invoke this function with a constant string
406 * literal and a headroom argument: you will likely end up invoking the
407 * version of copyBuffer() above. IOBuf::copyBuffer("hello", 3) will treat
408 * the first argument as a const void*, and will invoke the version of
409 * copyBuffer() above, with the size argument of 3.
411 static std::unique_ptr<IOBuf> copyBuffer(const std::string& buf,
413 uint64_t minTailroom=0);
414 IOBuf(CopyBufferOp op, const std::string& buf,
415 uint64_t headroom=0, uint64_t minTailroom=0)
416 : IOBuf(op, buf.data(), buf.size(), headroom, minTailroom) {}
419 * A version of copyBuffer() that returns a null pointer if the input string
422 static std::unique_ptr<IOBuf> maybeCopyBuffer(const std::string& buf,
424 uint64_t minTailroom=0);
427 * Convenience function to free a chain of IOBufs held by a unique_ptr.
429 static void destroy(std::unique_ptr<IOBuf>&& data) {
430 auto destroyer = std::move(data);
434 * Destroy this IOBuf.
436 * Deleting an IOBuf will automatically destroy all IOBufs in the chain.
437 * (See the comments above regarding the ownership model of IOBuf chains.
438 * All subsequent IOBufs in the chain are considered to be owned by the head
439 * of the chain. Users should only explicitly delete the head of a chain.)
441 * When each individual IOBuf is destroyed, it will release its reference
442 * count on the underlying buffer. If it was the last user of the buffer,
443 * the buffer will be freed.
448 * Check whether the chain is empty (i.e., whether the IOBufs in the
449 * chain have a total data length of zero).
451 * This method is semantically equivalent to
452 * i->computeChainDataLength()==0
453 * but may run faster because it can short-circuit as soon as it
454 * encounters a buffer with length()!=0
459 * Get the pointer to the start of the data.
461 const uint8_t* data() const {
466 * Get a writable pointer to the start of the data.
468 * The caller is responsible for calling unshare() first to ensure that it is
469 * actually safe to write to the buffer.
471 uint8_t* writableData() {
476 * Get the pointer to the end of the data.
478 const uint8_t* tail() const {
479 return data_ + length_;
483 * Get a writable pointer to the end of the data.
485 * The caller is responsible for calling unshare() first to ensure that it is
486 * actually safe to write to the buffer.
488 uint8_t* writableTail() {
489 return data_ + length_;
493 * Get the data length.
495 uint64_t length() const {
500 * Get the amount of head room.
502 * Returns the number of bytes in the buffer before the start of the data.
504 uint64_t headroom() const {
505 return data_ - buffer();
509 * Get the amount of tail room.
511 * Returns the number of bytes in the buffer after the end of the data.
513 uint64_t tailroom() const {
514 return bufferEnd() - tail();
518 * Get the pointer to the start of the buffer.
520 * Note that this is the pointer to the very beginning of the usable buffer,
521 * not the start of valid data within the buffer. Use the data() method to
522 * get a pointer to the start of the data within the buffer.
524 const uint8_t* buffer() const {
529 * Get a writable pointer to the start of the buffer.
531 * The caller is responsible for calling unshare() first to ensure that it is
532 * actually safe to write to the buffer.
534 uint8_t* writableBuffer() {
539 * Get the pointer to the end of the buffer.
541 * Note that this is the pointer to the very end of the usable buffer,
542 * not the end of valid data within the buffer. Use the tail() method to
543 * get a pointer to the end of the data within the buffer.
545 const uint8_t* bufferEnd() const {
546 return buf_ + capacity_;
550 * Get the total size of the buffer.
552 * This returns the total usable length of the buffer. Use the length()
553 * method to get the length of the actual valid data in this IOBuf.
555 uint64_t capacity() const {
560 * Get a pointer to the next IOBuf in this chain.
565 const IOBuf* next() const {
570 * Get a pointer to the previous IOBuf in this chain.
575 const IOBuf* prev() const {
580 * Shift the data forwards in the buffer.
582 * This shifts the data pointer forwards in the buffer to increase the
583 * headroom. This is commonly used to increase the headroom in a newly
586 * The caller is responsible for ensuring that there is sufficient
587 * tailroom in the buffer before calling advance().
589 * If there is a non-zero data length, advance() will use memmove() to shift
590 * the data forwards in the buffer. In this case, the caller is responsible
591 * for making sure the buffer is unshared, so it will not affect other IOBufs
592 * that may be sharing the same underlying buffer.
594 void advance(uint64_t amount) {
595 // In debug builds, assert if there is a problem.
596 assert(amount <= tailroom());
599 memmove(data_ + amount, data_, length_);
605 * Shift the data backwards in the buffer.
607 * The caller is responsible for ensuring that there is sufficient headroom
608 * in the buffer before calling retreat().
610 * If there is a non-zero data length, retreat() will use memmove() to shift
611 * the data backwards in the buffer. In this case, the caller is responsible
612 * for making sure the buffer is unshared, so it will not affect other IOBufs
613 * that may be sharing the same underlying buffer.
615 void retreat(uint64_t amount) {
616 // In debug builds, assert if there is a problem.
617 assert(amount <= headroom());
620 memmove(data_ - amount, data_, length_);
626 * Adjust the data pointer to include more valid data at the beginning.
628 * This moves the data pointer backwards to include more of the available
629 * buffer. The caller is responsible for ensuring that there is sufficient
630 * headroom for the new data. The caller is also responsible for populating
631 * this section with valid data.
633 * This does not modify any actual data in the buffer.
635 void prepend(uint64_t amount) {
636 DCHECK_LE(amount, headroom());
642 * Adjust the tail pointer to include more valid data at the end.
644 * This moves the tail pointer forwards to include more of the available
645 * buffer. The caller is responsible for ensuring that there is sufficient
646 * tailroom for the new data. The caller is also responsible for populating
647 * this section with valid data.
649 * This does not modify any actual data in the buffer.
651 void append(uint64_t amount) {
652 DCHECK_LE(amount, tailroom());
657 * Adjust the data pointer forwards to include less valid data.
659 * This moves the data pointer forwards so that the first amount bytes are no
660 * longer considered valid data. The caller is responsible for ensuring that
661 * amount is less than or equal to the actual data length.
663 * This does not modify any actual data in the buffer.
665 void trimStart(uint64_t amount) {
666 DCHECK_LE(amount, length_);
672 * Adjust the tail pointer backwards to include less valid data.
674 * This moves the tail pointer backwards so that the last amount bytes are no
675 * longer considered valid data. The caller is responsible for ensuring that
676 * amount is less than or equal to the actual data length.
678 * This does not modify any actual data in the buffer.
680 void trimEnd(uint64_t amount) {
681 DCHECK_LE(amount, length_);
688 * Postcondition: headroom() == 0, length() == 0, tailroom() == capacity()
691 data_ = writableBuffer();
696 * Ensure that this buffer has at least minHeadroom headroom bytes and at
697 * least minTailroom tailroom bytes. The buffer must be writable
698 * (you must call unshare() before this, if necessary).
700 * Postcondition: headroom() >= minHeadroom, tailroom() >= minTailroom,
701 * the data (between data() and data() + length()) is preserved.
703 void reserve(uint64_t minHeadroom, uint64_t minTailroom) {
704 // Maybe we don't need to do anything.
705 if (headroom() >= minHeadroom && tailroom() >= minTailroom) {
708 // If the buffer is empty but we have enough total room (head + tail),
709 // move the data_ pointer around.
711 headroom() + tailroom() >= minHeadroom + minTailroom) {
712 data_ = writableBuffer() + minHeadroom;
715 // Bah, we have to do actual work.
716 reserveSlow(minHeadroom, minTailroom);
720 * Return true if this IOBuf is part of a chain of multiple IOBufs, or false
721 * if this is the only IOBuf in its chain.
723 bool isChained() const {
724 assert((next_ == this) == (prev_ == this));
725 return next_ != this;
729 * Get the number of IOBufs in this chain.
731 * Beware that this method has to walk the entire chain.
732 * Use isChained() if you just want to check if this IOBuf is part of a chain
735 size_t countChainElements() const;
738 * Get the length of all the data in this IOBuf chain.
740 * Beware that this method has to walk the entire chain.
742 uint64_t computeChainDataLength() const;
745 * Insert another IOBuf chain immediately before this IOBuf.
747 * For example, if there are two IOBuf chains (A, B, C) and (D, E, F),
748 * and B->prependChain(D) is called, the (D, E, F) chain will be subsumed
749 * and become part of the chain starting at A, which will now look like
752 * Note that since IOBuf chains are circular, head->prependChain(other) can
753 * be used to append the other chain at the very end of the chain pointed to
754 * by head. For example, if there are two IOBuf chains (A, B, C) and
755 * (D, E, F), and A->prependChain(D) is called, the chain starting at A will
756 * now consist of (A, B, C, D, E, F)
758 * The elements in the specified IOBuf chain will become part of this chain,
759 * and will be owned by the head of this chain. When this chain is
760 * destroyed, all elements in the supplied chain will also be destroyed.
762 * For this reason, appendChain() only accepts an rvalue-reference to a
763 * unique_ptr(), to make it clear that it is taking ownership of the supplied
764 * chain. If you have a raw pointer, you can pass in a new temporary
765 * unique_ptr around the raw pointer. If you have an existing,
766 * non-temporary unique_ptr, you must call std::move(ptr) to make it clear
767 * that you are destroying the original pointer.
769 void prependChain(std::unique_ptr<IOBuf>&& iobuf);
772 * Append another IOBuf chain immediately after this IOBuf.
774 * For example, if there are two IOBuf chains (A, B, C) and (D, E, F),
775 * and B->appendChain(D) is called, the (D, E, F) chain will be subsumed
776 * and become part of the chain starting at A, which will now look like
779 * The elements in the specified IOBuf chain will become part of this chain,
780 * and will be owned by the head of this chain. When this chain is
781 * destroyed, all elements in the supplied chain will also be destroyed.
783 * For this reason, appendChain() only accepts an rvalue-reference to a
784 * unique_ptr(), to make it clear that it is taking ownership of the supplied
785 * chain. If you have a raw pointer, you can pass in a new temporary
786 * unique_ptr around the raw pointer. If you have an existing,
787 * non-temporary unique_ptr, you must call std::move(ptr) to make it clear
788 * that you are destroying the original pointer.
790 void appendChain(std::unique_ptr<IOBuf>&& iobuf) {
791 // Just use prependChain() on the next element in our chain
792 next_->prependChain(std::move(iobuf));
796 * Remove this IOBuf from its current chain.
798 * Since ownership of all elements an IOBuf chain is normally maintained by
799 * the head of the chain, unlink() transfers ownership of this IOBuf from the
800 * chain and gives it to the caller. A new unique_ptr to the IOBuf is
801 * returned to the caller. The caller must store the returned unique_ptr (or
802 * call release() on it) to take ownership, otherwise the IOBuf will be
803 * immediately destroyed.
805 * Since unlink transfers ownership of the IOBuf to the caller, be careful
806 * not to call unlink() on the head of a chain if you already maintain
807 * ownership on the head of the chain via other means. The pop() method
808 * is a better choice for that situation.
810 std::unique_ptr<IOBuf> unlink() {
811 next_->prev_ = prev_;
812 prev_->next_ = next_;
815 return std::unique_ptr<IOBuf>(this);
819 * Remove this IOBuf from its current chain and return a unique_ptr to
820 * the IOBuf that formerly followed it in the chain.
822 std::unique_ptr<IOBuf> pop() {
824 next_->prev_ = prev_;
825 prev_->next_ = next_;
828 return std::unique_ptr<IOBuf>((next == this) ? nullptr : next);
832 * Remove a subchain from this chain.
834 * Remove the subchain starting at head and ending at tail from this chain.
836 * Returns a unique_ptr pointing to head. (In other words, ownership of the
837 * head of the subchain is transferred to the caller.) If the caller ignores
838 * the return value and lets the unique_ptr be destroyed, the subchain will
839 * be immediately destroyed.
841 * The subchain referenced by the specified head and tail must be part of the
842 * same chain as the current IOBuf, but must not contain the current IOBuf.
843 * However, the specified head and tail may be equal to each other (i.e.,
844 * they may be a subchain of length 1).
846 std::unique_ptr<IOBuf> separateChain(IOBuf* head, IOBuf* tail) {
847 assert(head != this);
848 assert(tail != this);
850 head->prev_->next_ = tail->next_;
851 tail->next_->prev_ = head->prev_;
856 return std::unique_ptr<IOBuf>(head);
860 * Return true if at least one of the IOBufs in this chain are shared,
861 * or false if all of the IOBufs point to unique buffers.
863 * Use isSharedOne() to only check this IOBuf rather than the entire chain.
865 bool isShared() const {
866 const IOBuf* current = this;
868 if (current->isSharedOne()) {
871 current = current->next_;
872 if (current == this) {
879 * Return true if other IOBufs are also pointing to the buffer used by this
880 * IOBuf, and false otherwise.
882 * If this IOBuf points at a buffer owned by another (non-IOBuf) part of the
883 * code (i.e., if the IOBuf was created using wrapBuffer(), or was cloned
884 * from such an IOBuf), it is always considered shared.
886 * This only checks the current IOBuf, and not other IOBufs in the chain.
888 bool isSharedOne() const {
889 // If this is a user-owned buffer, it is always considered shared
890 if (UNLIKELY(!sharedInfo())) {
894 if (LIKELY(!(flags() & kFlagMaybeShared))) {
898 // kFlagMaybeShared is set, so we need to check the reference count.
899 // (Checking the reference count requires an atomic operation, which is why
900 // we prefer to only check kFlagMaybeShared if possible.)
901 bool shared = sharedInfo()->refcount.load(std::memory_order_acquire) > 1;
903 // we're the last one left
904 clearFlags(kFlagMaybeShared);
910 * Ensure that this IOBuf has a unique buffer that is not shared by other
913 * unshare() operates on an entire chain of IOBuf objects. If the chain is
914 * shared, it may also coalesce the chain when making it unique. If the
915 * chain is coalesced, subsequent IOBuf objects in the current chain will be
916 * automatically deleted.
918 * Note that buffers owned by other (non-IOBuf) users are automatically
921 * Throws std::bad_alloc on error. On error the IOBuf chain will be
924 * Currently unshare may also throw std::overflow_error if it tries to
925 * coalesce. (TODO: In the future it would be nice if unshare() were smart
926 * enough not to coalesce the entire buffer if the data is too large.
927 * However, in practice this seems unlikely to become an issue.)
938 * Ensure that this IOBuf has a unique buffer that is not shared by other
941 * unshareOne() operates on a single IOBuf object. This IOBuf will have a
942 * unique buffer after unshareOne() returns, but other IOBufs in the chain
943 * may still be shared after unshareOne() returns.
945 * Throws std::bad_alloc on error. On error the IOBuf will be unmodified.
954 * Coalesce this IOBuf chain into a single buffer.
956 * This method moves all of the data in this IOBuf chain into a single
957 * contiguous buffer, if it is not already in one buffer. After coalesce()
958 * returns, this IOBuf will be a chain of length one. Other IOBufs in the
959 * chain will be automatically deleted.
961 * After coalescing, the IOBuf will have at least as much headroom as the
962 * first IOBuf in the chain, and at least as much tailroom as the last IOBuf
965 * Throws std::bad_alloc on error. On error the IOBuf chain will be
968 * Returns ByteRange that points to the data IOBuf stores.
970 ByteRange coalesce() {
974 return ByteRange(data_, length_);
978 * Ensure that this chain has at least maxLength bytes available as a
979 * contiguous memory range.
981 * This method coalesces whole buffers in the chain into this buffer as
982 * necessary until this buffer's length() is at least maxLength.
984 * After coalescing, the IOBuf will have at least as much headroom as the
985 * first IOBuf in the chain, and at least as much tailroom as the last IOBuf
986 * that was coalesced.
988 * Throws std::bad_alloc or std::overflow_error on error. On error the IOBuf
989 * chain will be unmodified. Throws std::overflow_error if maxLength is
990 * longer than the total chain length.
992 * Upon return, either enough of the chain was coalesced into a contiguous
993 * region, or the entire chain was coalesced. That is,
994 * length() >= maxLength || !isChained() is true.
996 void gather(uint64_t maxLength) {
997 if (!isChained() || length_ >= maxLength) {
1000 coalesceSlow(maxLength);
1004 * Return a new IOBuf chain sharing the same data as this chain.
1006 * The new IOBuf chain will normally point to the same underlying data
1007 * buffers as the original chain. (The one exception to this is if some of
1008 * the IOBufs in this chain contain small internal data buffers which cannot
1011 std::unique_ptr<IOBuf> clone() const;
1014 * Return a new IOBuf with the same data as this IOBuf.
1016 * The new IOBuf returned will not be part of a chain (even if this IOBuf is
1017 * part of a larger chain).
1019 std::unique_ptr<IOBuf> cloneOne() const;
1022 * Similar to Clone(). But use other as the head node. Other nodes in the
1023 * chain (if any) will be allocted on heap.
1025 void cloneInto(IOBuf& other) const;
1028 * Similar to CloneOne(). But to fill an existing IOBuf instead of a new
1031 void cloneOneInto(IOBuf& other) const;
1034 * Return an iovector suitable for e.g. writev()
1036 * auto iov = buf->getIov();
1037 * auto xfer = writev(fd, iov.data(), iov.size());
1039 * Naturally, the returned iovector is invalid if you modify the buffer
1042 folly::fbvector<struct iovec> getIov() const;
1045 * Overridden operator new and delete.
1046 * These perform specialized memory management to help support
1047 * createCombined(), which allocates IOBuf objects together with the buffer
1050 void* operator new(size_t size);
1051 void* operator new(size_t size, void* ptr);
1052 void operator delete(void* ptr);
1055 * Destructively convert this IOBuf to a fbstring efficiently.
1056 * We rely on fbstring's AcquireMallocatedString constructor to
1059 fbstring moveToFbString();
1062 * Iteration support: a chain of IOBufs may be iterated through using
1063 * STL-style iterators over const ByteRanges. Iterators are only invalidated
1064 * if the IOBuf that they currently point to is removed.
1066 Iterator cbegin() const;
1067 Iterator cend() const;
1068 Iterator begin() const;
1069 Iterator end() const;
1072 * Allocate a new null buffer.
1074 * This can be used to allocate an empty IOBuf on the stack. It will have no
1075 * space allocated for it. This is generally useful only to later use move
1076 * assignment to fill out the IOBuf.
1081 * Move constructor and assignment operator.
1083 * In general, you should only ever move the head of an IOBuf chain.
1084 * Internal nodes in an IOBuf chain are owned by the head of the chain, and
1085 * should not be moved from. (Technically, nothing prevents you from moving
1086 * a non-head node, but the moved-to node will replace the moved-from node in
1087 * the chain. This has implications for ownership, since non-head nodes are
1088 * owned by the chain head. You are then responsible for relinquishing
1089 * ownership of the moved-to node, and manually deleting the moved-from
1092 * With the move assignment operator, the destination of the move should be
1093 * the head of an IOBuf chain or a solitary IOBuf not part of a chain. If
1094 * the move destination is part of a chain, all other IOBufs in the chain
1097 * (We currently don't provide a copy constructor or assignment operator.
1098 * The main reason is because it is not clear these operations should copy
1099 * the entire chain or just the single IOBuf.)
1101 IOBuf(IOBuf&& other) noexcept;
1102 IOBuf& operator=(IOBuf&& other) noexcept;
1105 enum FlagsEnum : uintptr_t {
1106 // Adding any more flags would not work on 32-bit architectures,
1107 // as these flags are stashed in the least significant 2 bits of a
1108 // max-align-aligned pointer.
1109 kFlagFreeSharedInfo = 0x1,
1110 kFlagMaybeShared = 0x2,
1111 kFlagMask = kFlagFreeSharedInfo | kFlagMaybeShared
1116 SharedInfo(FreeFunction fn, void* arg);
1118 // A pointer to a function to call to free the buffer when the refcount
1119 // hits 0. If this is null, free() will be used instead.
1120 FreeFunction freeFn;
1122 std::atomic<uint32_t> refcount;
1124 // Helper structs for use by operator new and delete
1127 struct HeapFullStorage;
1129 // Forbidden copy constructor and assignment opererator
1130 IOBuf(IOBuf const &);
1131 IOBuf& operator=(IOBuf const &);
1134 * Create a new IOBuf pointing to an external buffer.
1136 * The caller is responsible for holding a reference count for this new
1137 * IOBuf. The IOBuf constructor does not automatically increment the
1140 struct InternalConstructor {}; // avoid conflicts
1141 IOBuf(InternalConstructor, uintptr_t flagsAndSharedInfo,
1142 uint8_t* buf, uint64_t capacity,
1143 uint8_t* data, uint64_t length);
1145 void unshareOneSlow();
1146 void unshareChained();
1147 void coalesceSlow();
1148 void coalesceSlow(size_t maxLength);
1149 // newLength must be the entire length of the buffers between this and
1150 // end (no truncation)
1151 void coalesceAndReallocate(
1155 size_t newTailroom);
1156 void coalesceAndReallocate(size_t newLength, IOBuf* end) {
1157 coalesceAndReallocate(headroom(), newLength, end, end->prev_->tailroom());
1159 void decrementRefcount();
1160 void reserveSlow(uint64_t minHeadroom, uint64_t minTailroom);
1161 void freeExtBuffer();
1163 static size_t goodExtBufferSize(uint64_t minCapacity);
1164 static void initExtBuffer(uint8_t* buf, size_t mallocSize,
1165 SharedInfo** infoReturn,
1166 uint64_t* capacityReturn);
1167 static void allocExtBuffer(uint64_t minCapacity,
1168 uint8_t** bufReturn,
1169 SharedInfo** infoReturn,
1170 uint64_t* capacityReturn);
1171 static void releaseStorage(HeapStorage* storage, uint16_t freeFlags);
1172 static void freeInternalBuf(void* buf, void* userData);
1179 * Links to the next and the previous IOBuf in this chain.
1181 * The chain is circularly linked (the last element in the chain points back
1182 * at the head), and next_ and prev_ can never be null. If this IOBuf is the
1183 * only element in the chain, next_ and prev_ will both point to this.
1189 * A pointer to the start of the data referenced by this IOBuf, and the
1190 * length of the data.
1192 * This may refer to any subsection of the actual buffer capacity.
1194 uint8_t* data_{nullptr};
1195 uint8_t* buf_{nullptr};
1196 uint64_t length_{0};
1197 uint64_t capacity_{0};
1199 // Pack flags in least significant 2 bits, sharedInfo in the rest
1200 mutable uintptr_t flagsAndSharedInfo_{0};
1202 static inline uintptr_t packFlagsAndSharedInfo(uintptr_t flags,
1204 uintptr_t uinfo = reinterpret_cast<uintptr_t>(info);
1205 DCHECK_EQ(flags & ~kFlagMask, 0);
1206 DCHECK_EQ(uinfo & kFlagMask, 0);
1207 return flags | uinfo;
1210 inline SharedInfo* sharedInfo() const {
1211 return reinterpret_cast<SharedInfo*>(flagsAndSharedInfo_ & ~kFlagMask);
1214 inline void setSharedInfo(SharedInfo* info) {
1215 uintptr_t uinfo = reinterpret_cast<uintptr_t>(info);
1216 DCHECK_EQ(uinfo & kFlagMask, 0);
1217 flagsAndSharedInfo_ = (flagsAndSharedInfo_ & kFlagMask) | uinfo;
1220 inline uintptr_t flags() const {
1221 return flagsAndSharedInfo_ & kFlagMask;
1224 // flags_ are changed from const methods
1225 inline void setFlags(uintptr_t flags) const {
1226 DCHECK_EQ(flags & ~kFlagMask, 0);
1227 flagsAndSharedInfo_ |= flags;
1230 inline void clearFlags(uintptr_t flags) const {
1231 DCHECK_EQ(flags & ~kFlagMask, 0);
1232 flagsAndSharedInfo_ &= ~flags;
1235 inline void setFlagsAndSharedInfo(uintptr_t flags, SharedInfo* info) {
1236 flagsAndSharedInfo_ = packFlagsAndSharedInfo(flags, info);
1239 struct DeleterBase {
1240 virtual ~DeleterBase() { }
1241 virtual void dispose(void* p) = 0;
1244 template <class UniquePtr>
1245 struct UniquePtrDeleter : public DeleterBase {
1246 typedef typename UniquePtr::pointer Pointer;
1247 typedef typename UniquePtr::deleter_type Deleter;
1249 explicit UniquePtrDeleter(Deleter deleter) : deleter_(std::move(deleter)){ }
1250 void dispose(void* p) {
1252 deleter_(static_cast<Pointer>(p));
1263 static void freeUniquePtrBuffer(void* ptr, void* userData) {
1264 static_cast<DeleterBase*>(userData)->dispose(ptr);
1269 * Hasher for IOBuf objects. Hashes the entire chain using SpookyHashV2.
1272 size_t operator()(const IOBuf& buf) const;
1273 size_t operator()(const std::unique_ptr<IOBuf>& buf) const {
1274 return buf ? (*this)(*buf) : 0;
1279 * Equality predicate for IOBuf objects. Compares data in the entire chain.
1282 bool operator()(const IOBuf& a, const IOBuf& b) const;
1283 bool operator()(const std::unique_ptr<IOBuf>& a,
1284 const std::unique_ptr<IOBuf>& b) const {
1287 } else if (!a || !b) {
1290 return (*this)(*a, *b);
1295 template <class UniquePtr>
1296 typename std::enable_if<detail::IsUniquePtrToSL<UniquePtr>::value,
1297 std::unique_ptr<IOBuf>>::type
1298 IOBuf::takeOwnership(UniquePtr&& buf, size_t count) {
1299 size_t size = count * sizeof(typename UniquePtr::element_type);
1300 auto deleter = new UniquePtrDeleter<UniquePtr>(buf.get_deleter());
1301 return takeOwnership(buf.release(),
1303 &IOBuf::freeUniquePtrBuffer,
1307 inline std::unique_ptr<IOBuf> IOBuf::copyBuffer(
1308 const void* data, uint64_t size, uint64_t headroom,
1309 uint64_t minTailroom) {
1310 uint64_t capacity = headroom + size + minTailroom;
1311 std::unique_ptr<IOBuf> buf = create(capacity);
1312 buf->advance(headroom);
1313 memcpy(buf->writableData(), data, size);
1318 inline std::unique_ptr<IOBuf> IOBuf::copyBuffer(const std::string& buf,
1320 uint64_t minTailroom) {
1321 return copyBuffer(buf.data(), buf.size(), headroom, minTailroom);
1324 inline std::unique_ptr<IOBuf> IOBuf::maybeCopyBuffer(const std::string& buf,
1326 uint64_t minTailroom) {
1330 return copyBuffer(buf.data(), buf.size(), headroom, minTailroom);
1333 class IOBuf::Iterator : public boost::iterator_facade<
1334 IOBuf::Iterator, // Derived
1335 const ByteRange, // Value
1336 boost::forward_traversal_tag // Category or traversal
1338 friend class boost::iterator_core_access;
1340 // Note that IOBufs are stored as a circular list without a guard node,
1341 // so pos == end is ambiguous (it may mean "begin" or "end"). To solve
1342 // the ambiguity (at the cost of one extra comparison in the "increment"
1343 // code path), we define end iterators as having pos_ == end_ == nullptr
1344 // and we only allow forward iteration.
1345 explicit Iterator(const IOBuf* pos, const IOBuf* end)
1348 // Sadly, we must return by const reference, not by value.
1356 val_ = ByteRange(pos_->data(), pos_->tail());
1359 void adjustForEnd() {
1361 pos_ = end_ = nullptr;
1368 const ByteRange& dereference() const {
1372 bool equal(const Iterator& other) const {
1373 // We must compare end_ in addition to pos_, because forward traversal
1374 // requires that if two iterators are equal (a == b) and dereferenceable,
1376 return pos_ == other.pos_ && end_ == other.end_;
1380 pos_ = pos_->next();
1389 inline IOBuf::Iterator IOBuf::begin() const { return cbegin(); }
1390 inline IOBuf::Iterator IOBuf::end() const { return cend(); }
1394 #pragma GCC diagnostic pop
1396 #endif // FOLLY_IO_IOBUF_H_