2 * Copyright 2013 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/Sharing
169 * -------------------------------
171 * IOBuf objects themselves are always allocated on the heap. The IOBuf
172 * constructors are private, so IOBuf objects may not be created on the stack.
173 * In part this is done since some IOBuf objects use small-buffer optimization
174 * and contain the buffer data immediately after the IOBuf object itself. The
175 * coalesce() and unshare() methods also expect to be able to delete subsequent
176 * IOBuf objects in the chain if they are no longer needed due to coalescing.
178 * The IOBuf structure also does not provide room for an intrusive refcount on
179 * the IOBuf object itself, only the underlying data buffer is reference
180 * counted. If users want to share the same IOBuf object between multiple
181 * parts of the code, they are responsible for managing this sharing on their
182 * own. (For example, by using a shared_ptr. Alternatively, users always have
183 * the option of using clone() to create a second IOBuf that points to the same
184 * underlying buffer.)
186 * With jemalloc, allocating small objects like IOBuf objects should be
187 * relatively fast, and the cost of allocating IOBuf objects on the heap and
188 * cloning new IOBufs should be relatively cheap.
191 // Is T a unique_ptr<> to a standard-layout type?
192 template <class T, class Enable=void> struct IsUniquePtrToSL
193 : public std::false_type { };
194 template <class T, class D>
195 struct IsUniquePtrToSL<
196 std::unique_ptr<T, D>,
197 typename std::enable_if<std::is_standard_layout<T>::value>::type>
198 : public std::true_type { };
199 } // namespace detail
205 typedef ByteRange value_type;
206 typedef Iterator iterator;
207 typedef Iterator const_iterator;
209 typedef void (*FreeFunction)(void* buf, void* userData);
212 * Allocate a new IOBuf object with the requested capacity.
214 * Returns a new IOBuf object that must be (eventually) deleted by the
215 * caller. The returned IOBuf may actually have slightly more capacity than
218 * The data pointer will initially point to the start of the newly allocated
219 * buffer, and will have a data length of 0.
221 * Throws std::bad_alloc on error.
223 static std::unique_ptr<IOBuf> create(uint32_t capacity);
226 * Create a new IOBuf, using a single memory allocation to allocate space
227 * for both the IOBuf object and the data storage space.
229 * This saves one memory allocation. However, it can be wasteful if you
230 * later need to grow the buffer using reserve(). If the buffer needs to be
231 * reallocated, the space originally allocated will not be freed() until the
232 * IOBuf object itself is also freed. (It can also be slightly wasteful in
233 * some cases where you clone this IOBuf and then free the original IOBuf.)
235 static std::unique_ptr<IOBuf> createCombined(uint32_t capacity);
238 * Create a new IOBuf, using separate memory allocations for the IOBuf object
239 * for the IOBuf and the data storage space.
241 * This requires two memory allocations, but saves space in the long run
242 * if you know that you will need to reallocate the data buffer later.
244 static std::unique_ptr<IOBuf> createSeparate(uint32_t capacity);
247 * Allocate a new IOBuf chain with the requested total capacity, allocating
248 * no more than maxBufCapacity to each buffer.
250 static std::unique_ptr<IOBuf> createChain(
251 size_t totalCapacity, uint32_t maxBufCapacity);
254 * Create a new IOBuf pointing to an existing data buffer.
256 * The new IOBuffer will assume ownership of the buffer, and free it by
257 * calling the specified FreeFunction when the last IOBuf pointing to this
258 * buffer is destroyed. The function will be called with a pointer to the
259 * buffer as the first argument, and the supplied userData value as the
260 * second argument. The free function must never throw exceptions.
262 * If no FreeFunction is specified, the buffer will be freed using free()
263 * which will result in undefined behavior if the memory was allocated
266 * The IOBuf data pointer will initially point to the start of the buffer,
268 * In the first version of this function, the length of data is unspecified
269 * and is initialized to the capacity of the buffer
271 * In the second version, the user specifies the valid length of data
274 * On error, std::bad_alloc will be thrown. If freeOnError is true (the
275 * default) the buffer will be freed before throwing the error.
277 static std::unique_ptr<IOBuf> takeOwnership(void* buf, uint32_t capacity,
278 FreeFunction freeFn = NULL,
279 void* userData = NULL,
280 bool freeOnError = true) {
281 return takeOwnership(buf, capacity, capacity, freeFn,
282 userData, freeOnError);
285 static std::unique_ptr<IOBuf> takeOwnership(void* buf, uint32_t capacity,
287 FreeFunction freeFn = NULL,
288 void* userData = NULL,
289 bool freeOnError = true);
292 * Create a new IOBuf pointing to an existing data buffer made up of
293 * count objects of a given standard-layout type.
295 * This is dangerous -- it is essentially equivalent to doing
296 * reinterpret_cast<unsigned char*> on your data -- but it's often useful
297 * for serialization / deserialization.
299 * The new IOBuffer will assume ownership of the buffer, and free it
300 * appropriately (by calling the UniquePtr's custom deleter, or by calling
301 * delete or delete[] appropriately if there is no custom deleter)
302 * when the buffer is destroyed. The custom deleter, if any, must never
305 * The IOBuf data pointer will initially point to the start of the buffer,
306 * and the length will be the full capacity of the buffer (count *
309 * On error, std::bad_alloc will be thrown, and the buffer will be freed
310 * before throwing the error.
312 template <class UniquePtr>
313 static typename std::enable_if<detail::IsUniquePtrToSL<UniquePtr>::value,
314 std::unique_ptr<IOBuf>>::type
315 takeOwnership(UniquePtr&& buf, size_t count=1);
318 * Create a new IOBuf object that points to an existing user-owned buffer.
320 * This should only be used when the caller knows the lifetime of the IOBuf
321 * object ahead of time and can ensure that all IOBuf objects that will point
322 * to this buffer will be destroyed before the buffer itself is destroyed.
324 * This buffer will not be freed automatically when the last IOBuf
325 * referencing it is destroyed. It is the caller's responsibility to free
326 * the buffer after the last IOBuf has been destroyed.
328 * The IOBuf data pointer will initially point to the start of the buffer,
329 * and the length will be the full capacity of the buffer.
331 * An IOBuf created using wrapBuffer() will always be reported as shared.
332 * unshare() may be used to create a writable copy of the buffer.
334 * On error, std::bad_alloc will be thrown.
336 static std::unique_ptr<IOBuf> wrapBuffer(const void* buf, uint32_t capacity);
337 static std::unique_ptr<IOBuf> wrapBuffer(ByteRange br) {
338 CHECK_LE(br.size(), std::numeric_limits<uint32_t>::max());
339 return wrapBuffer(br.data(), br.size());
343 * Convenience function to create a new IOBuf object that copies data from a
344 * user-supplied buffer, optionally allocating a given amount of
345 * headroom and tailroom.
347 static std::unique_ptr<IOBuf> copyBuffer(const void* buf, uint32_t size,
349 uint32_t minTailroom=0);
350 static std::unique_ptr<IOBuf> copyBuffer(ByteRange br,
352 uint32_t minTailroom=0) {
353 CHECK_LE(br.size(), std::numeric_limits<uint32_t>::max());
354 return copyBuffer(br.data(), br.size(), headroom, minTailroom);
358 * Convenience function to create a new IOBuf object that copies data from a
359 * user-supplied string, optionally allocating a given amount of
360 * headroom and tailroom.
362 * Beware when attempting to invoke this function with a constant string
363 * literal and a headroom argument: you will likely end up invoking the
364 * version of copyBuffer() above. IOBuf::copyBuffer("hello", 3) will treat
365 * the first argument as a const void*, and will invoke the version of
366 * copyBuffer() above, with the size argument of 3.
368 static std::unique_ptr<IOBuf> copyBuffer(const std::string& buf,
370 uint32_t minTailroom=0);
373 * A version of copyBuffer() that returns a null pointer if the input string
376 static std::unique_ptr<IOBuf> maybeCopyBuffer(const std::string& buf,
378 uint32_t minTailroom=0);
381 * Convenience function to free a chain of IOBufs held by a unique_ptr.
383 static void destroy(std::unique_ptr<IOBuf>&& data) {
384 auto destroyer = std::move(data);
388 * Destroy this IOBuf.
390 * Deleting an IOBuf will automatically destroy all IOBufs in the chain.
391 * (See the comments above regarding the ownership model of IOBuf chains.
392 * All subsequent IOBufs in the chain are considered to be owned by the head
393 * of the chain. Users should only explicitly delete the head of a chain.)
395 * When each individual IOBuf is destroyed, it will release its reference
396 * count on the underlying buffer. If it was the last user of the buffer,
397 * the buffer will be freed.
402 * Check whether the chain is empty (i.e., whether the IOBufs in the
403 * chain have a total data length of zero).
405 * This method is semantically equivalent to
406 * i->computeChainDataLength()==0
407 * but may run faster because it can short-circuit as soon as it
408 * encounters a buffer with length()!=0
413 * Get the pointer to the start of the data.
415 const uint8_t* data() const {
420 * Get a writable pointer to the start of the data.
422 * The caller is responsible for calling unshare() first to ensure that it is
423 * actually safe to write to the buffer.
425 uint8_t* writableData() {
430 * Get the pointer to the end of the data.
432 const uint8_t* tail() const {
433 return data_ + length_;
437 * Get a writable pointer to the end of the data.
439 * The caller is responsible for calling unshare() first to ensure that it is
440 * actually safe to write to the buffer.
442 uint8_t* writableTail() {
443 return data_ + length_;
447 * Get the data length.
449 uint32_t length() const {
454 * Get the amount of head room.
456 * Returns the number of bytes in the buffer before the start of the data.
458 uint32_t headroom() const {
459 return data_ - buffer();
463 * Get the amount of tail room.
465 * Returns the number of bytes in the buffer after the end of the data.
467 uint32_t tailroom() const {
468 return bufferEnd() - tail();
472 * Get the pointer to the start of the buffer.
474 * Note that this is the pointer to the very beginning of the usable buffer,
475 * not the start of valid data within the buffer. Use the data() method to
476 * get a pointer to the start of the data within the buffer.
478 const uint8_t* buffer() const {
483 * Get a writable pointer to the start of the buffer.
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* writableBuffer() {
493 * Get the pointer to the end of the buffer.
495 * Note that this is the pointer to the very end of the usable buffer,
496 * not the end of valid data within the buffer. Use the tail() method to
497 * get a pointer to the end of the data within the buffer.
499 const uint8_t* bufferEnd() const {
500 return buf_ + capacity_;
504 * Get the total size of the buffer.
506 * This returns the total usable length of the buffer. Use the length()
507 * method to get the length of the actual valid data in this IOBuf.
509 uint32_t capacity() const {
514 * Get a pointer to the next IOBuf in this chain.
519 const IOBuf* next() const {
524 * Get a pointer to the previous IOBuf in this chain.
529 const IOBuf* prev() const {
534 * Shift the data forwards in the buffer.
536 * This shifts the data pointer forwards in the buffer to increase the
537 * headroom. This is commonly used to increase the headroom in a newly
540 * The caller is responsible for ensuring that there is sufficient
541 * tailroom in the buffer before calling advance().
543 * If there is a non-zero data length, advance() will use memmove() to shift
544 * the data forwards in the buffer. In this case, the caller is responsible
545 * for making sure the buffer is unshared, so it will not affect other IOBufs
546 * that may be sharing the same underlying buffer.
548 void advance(uint32_t amount) {
549 // In debug builds, assert if there is a problem.
550 assert(amount <= tailroom());
553 memmove(data_ + amount, data_, length_);
559 * Shift the data backwards in the buffer.
561 * The caller is responsible for ensuring that there is sufficient headroom
562 * in the buffer before calling retreat().
564 * If there is a non-zero data length, retreat() will use memmove() to shift
565 * the data backwards in the buffer. In this case, the caller is responsible
566 * for making sure the buffer is unshared, so it will not affect other IOBufs
567 * that may be sharing the same underlying buffer.
569 void retreat(uint32_t amount) {
570 // In debug builds, assert if there is a problem.
571 assert(amount <= headroom());
574 memmove(data_ - amount, data_, length_);
580 * Adjust the data pointer to include more valid data at the beginning.
582 * This moves the data pointer backwards to include more of the available
583 * buffer. The caller is responsible for ensuring that there is sufficient
584 * headroom for the new data. The caller is also responsible for populating
585 * this section with valid data.
587 * This does not modify any actual data in the buffer.
589 void prepend(uint32_t amount) {
590 DCHECK_LE(amount, headroom());
596 * Adjust the tail pointer to include more valid data at the end.
598 * This moves the tail pointer forwards to include more of the available
599 * buffer. The caller is responsible for ensuring that there is sufficient
600 * tailroom for the new data. The caller is also responsible for populating
601 * this section with valid data.
603 * This does not modify any actual data in the buffer.
605 void append(uint32_t amount) {
606 DCHECK_LE(amount, tailroom());
611 * Adjust the data pointer forwards to include less valid data.
613 * This moves the data pointer forwards so that the first amount bytes are no
614 * longer considered valid data. The caller is responsible for ensuring that
615 * amount is less than or equal to the actual data length.
617 * This does not modify any actual data in the buffer.
619 void trimStart(uint32_t amount) {
620 DCHECK_LE(amount, length_);
626 * Adjust the tail pointer backwards to include less valid data.
628 * This moves the tail pointer backwards so that the last amount bytes are no
629 * longer considered valid data. The caller is responsible for ensuring that
630 * amount is less than or equal to the actual data length.
632 * This does not modify any actual data in the buffer.
634 void trimEnd(uint32_t amount) {
635 DCHECK_LE(amount, length_);
642 * Postcondition: headroom() == 0, length() == 0, tailroom() == capacity()
645 data_ = writableBuffer();
650 * Ensure that this buffer has at least minHeadroom headroom bytes and at
651 * least minTailroom tailroom bytes. The buffer must be writable
652 * (you must call unshare() before this, if necessary).
654 * Postcondition: headroom() >= minHeadroom, tailroom() >= minTailroom,
655 * the data (between data() and data() + length()) is preserved.
657 void reserve(uint32_t minHeadroom, uint32_t minTailroom) {
658 // Maybe we don't need to do anything.
659 if (headroom() >= minHeadroom && tailroom() >= minTailroom) {
662 // If the buffer is empty but we have enough total room (head + tail),
663 // move the data_ pointer around.
665 headroom() + tailroom() >= minHeadroom + minTailroom) {
666 data_ = writableBuffer() + minHeadroom;
669 // Bah, we have to do actual work.
670 reserveSlow(minHeadroom, minTailroom);
674 * Return true if this IOBuf is part of a chain of multiple IOBufs, or false
675 * if this is the only IOBuf in its chain.
677 bool isChained() const {
678 assert((next_ == this) == (prev_ == this));
679 return next_ != this;
683 * Get the number of IOBufs in this chain.
685 * Beware that this method has to walk the entire chain.
686 * Use isChained() if you just want to check if this IOBuf is part of a chain
689 uint32_t countChainElements() const;
692 * Get the length of all the data in this IOBuf chain.
694 * Beware that this method has to walk the entire chain.
696 uint64_t computeChainDataLength() const;
699 * Insert another IOBuf chain immediately before this IOBuf.
701 * For example, if there are two IOBuf chains (A, B, C) and (D, E, F),
702 * and B->prependChain(D) is called, the (D, E, F) chain will be subsumed
703 * and become part of the chain starting at A, which will now look like
706 * Note that since IOBuf chains are circular, head->prependChain(other) can
707 * be used to append the other chain at the very end of the chain pointed to
708 * by head. For example, if there are two IOBuf chains (A, B, C) and
709 * (D, E, F), and A->prependChain(D) is called, the chain starting at A will
710 * now consist of (A, B, C, D, E, F)
712 * The elements in the specified IOBuf chain will become part of this chain,
713 * and will be owned by the head of this chain. When this chain is
714 * destroyed, all elements in the supplied chain will also be destroyed.
716 * For this reason, appendChain() only accepts an rvalue-reference to a
717 * unique_ptr(), to make it clear that it is taking ownership of the supplied
718 * chain. If you have a raw pointer, you can pass in a new temporary
719 * unique_ptr around the raw pointer. If you have an existing,
720 * non-temporary unique_ptr, you must call std::move(ptr) to make it clear
721 * that you are destroying the original pointer.
723 void prependChain(std::unique_ptr<IOBuf>&& iobuf);
726 * Append another IOBuf chain immediately after this IOBuf.
728 * For example, if there are two IOBuf chains (A, B, C) and (D, E, F),
729 * and B->appendChain(D) is called, the (D, E, F) chain will be subsumed
730 * and become part of the chain starting at A, which will now look like
733 * The elements in the specified IOBuf chain will become part of this chain,
734 * and will be owned by the head of this chain. When this chain is
735 * destroyed, all elements in the supplied chain will also be destroyed.
737 * For this reason, appendChain() only accepts an rvalue-reference to a
738 * unique_ptr(), to make it clear that it is taking ownership of the supplied
739 * chain. If you have a raw pointer, you can pass in a new temporary
740 * unique_ptr around the raw pointer. If you have an existing,
741 * non-temporary unique_ptr, you must call std::move(ptr) to make it clear
742 * that you are destroying the original pointer.
744 void appendChain(std::unique_ptr<IOBuf>&& iobuf) {
745 // Just use prependChain() on the next element in our chain
746 next_->prependChain(std::move(iobuf));
750 * Remove this IOBuf from its current chain.
752 * Since ownership of all elements an IOBuf chain is normally maintained by
753 * the head of the chain, unlink() transfers ownership of this IOBuf from the
754 * chain and gives it to the caller. A new unique_ptr to the IOBuf is
755 * returned to the caller. The caller must store the returned unique_ptr (or
756 * call release() on it) to take ownership, otherwise the IOBuf will be
757 * immediately destroyed.
759 * Since unlink transfers ownership of the IOBuf to the caller, be careful
760 * not to call unlink() on the head of a chain if you already maintain
761 * ownership on the head of the chain via other means. The pop() method
762 * is a better choice for that situation.
764 std::unique_ptr<IOBuf> unlink() {
765 next_->prev_ = prev_;
766 prev_->next_ = next_;
769 return std::unique_ptr<IOBuf>(this);
773 * Remove this IOBuf from its current chain and return a unique_ptr to
774 * the IOBuf that formerly followed it in the chain.
776 std::unique_ptr<IOBuf> pop() {
778 next_->prev_ = prev_;
779 prev_->next_ = next_;
782 return std::unique_ptr<IOBuf>((next == this) ? NULL : next);
786 * Remove a subchain from this chain.
788 * Remove the subchain starting at head and ending at tail from this chain.
790 * Returns a unique_ptr pointing to head. (In other words, ownership of the
791 * head of the subchain is transferred to the caller.) If the caller ignores
792 * the return value and lets the unique_ptr be destroyed, the subchain will
793 * be immediately destroyed.
795 * The subchain referenced by the specified head and tail must be part of the
796 * same chain as the current IOBuf, but must not contain the current IOBuf.
797 * However, the specified head and tail may be equal to each other (i.e.,
798 * they may be a subchain of length 1).
800 std::unique_ptr<IOBuf> separateChain(IOBuf* head, IOBuf* tail) {
801 assert(head != this);
802 assert(tail != this);
804 head->prev_->next_ = tail->next_;
805 tail->next_->prev_ = head->prev_;
810 return std::unique_ptr<IOBuf>(head);
814 * Return true if at least one of the IOBufs in this chain are shared,
815 * or false if all of the IOBufs point to unique buffers.
817 * Use isSharedOne() to only check this IOBuf rather than the entire chain.
819 bool isShared() const {
820 const IOBuf* current = this;
822 if (current->isSharedOne()) {
825 current = current->next_;
826 if (current == this) {
833 * Return true if other IOBufs are also pointing to the buffer used by this
834 * IOBuf, and false otherwise.
836 * If this IOBuf points at a buffer owned by another (non-IOBuf) part of the
837 * code (i.e., if the IOBuf was created using wrapBuffer(), or was cloned
838 * from such an IOBuf), it is always considered shared.
840 * This only checks the current IOBuf, and not other IOBufs in the chain.
842 bool isSharedOne() const {
843 if (LIKELY(flags_ & (kFlagUserOwned | kFlagMaybeShared)) == 0) {
847 // If this is a user-owned buffer, it is always considered shared
848 if (flags_ & kFlagUserOwned) {
852 // kFlagMaybeShared is set, so we need to check the reference count.
853 // (Checking the reference count requires an atomic operation, which is why
854 // we prefer to only check kFlagMaybeShared if possible.)
855 DCHECK(flags_ & kFlagMaybeShared);
856 bool shared = sharedInfo_->refcount.load(std::memory_order_acquire) > 1;
858 // we're the last one left
859 flags_ &= ~kFlagMaybeShared;
865 * Ensure that this IOBuf has a unique buffer that is not shared by other
868 * unshare() operates on an entire chain of IOBuf objects. If the chain is
869 * shared, it may also coalesce the chain when making it unique. If the
870 * chain is coalesced, subsequent IOBuf objects in the current chain will be
871 * automatically deleted.
873 * Note that buffers owned by other (non-IOBuf) users are automatically
876 * Throws std::bad_alloc on error. On error the IOBuf chain will be
879 * Currently unshare may also throw std::overflow_error if it tries to
880 * coalesce. (TODO: In the future it would be nice if unshare() were smart
881 * enough not to coalesce the entire buffer if the data is too large.
882 * However, in practice this seems unlikely to become an issue.)
893 * Ensure that this IOBuf has a unique buffer that is not shared by other
896 * unshareOne() operates on a single IOBuf object. This IOBuf will have a
897 * unique buffer after unshareOne() returns, but other IOBufs in the chain
898 * may still be shared after unshareOne() returns.
900 * Throws std::bad_alloc on error. On error the IOBuf will be unmodified.
909 * Coalesce this IOBuf chain into a single buffer.
911 * This method moves all of the data in this IOBuf chain into a single
912 * contiguous buffer, if it is not already in one buffer. After coalesce()
913 * returns, this IOBuf will be a chain of length one. Other IOBufs in the
914 * chain will be automatically deleted.
916 * After coalescing, the IOBuf will have at least as much headroom as the
917 * first IOBuf in the chain, and at least as much tailroom as the last IOBuf
920 * Throws std::bad_alloc on error. On error the IOBuf chain will be
921 * unmodified. Throws std::overflow_error if the length of the entire chain
922 * larger than can be described by a uint32_t capacity.
924 * Returns ByteRange that points to the data IOBuf stores.
926 ByteRange coalesce() {
930 return ByteRange(data_, length_);
934 * Ensure that this chain has at least maxLength bytes available as a
935 * contiguous memory range.
937 * This method coalesces whole buffers in the chain into this buffer as
938 * necessary until this buffer's length() is at least maxLength.
940 * After coalescing, the IOBuf will have at least as much headroom as the
941 * first IOBuf in the chain, and at least as much tailroom as the last IOBuf
942 * that was coalesced.
944 * Throws std::bad_alloc on error. On error the IOBuf chain will be
945 * unmodified. Throws std::overflow_error if the length of the coalesced
946 * portion of the chain is larger than can be described by a uint32_t
947 * capacity. (Although maxLength is uint32_t, gather() doesn't split
948 * buffers, so coalescing whole buffers may result in a capacity that can't
949 * be described in uint32_t.
951 * Upon return, either enough of the chain was coalesced into a contiguous
952 * region, or the entire chain was coalesced. That is,
953 * length() >= maxLength || !isChained() is true.
955 void gather(uint32_t maxLength) {
956 if (!isChained() || length_ >= maxLength) {
959 coalesceSlow(maxLength);
963 * Return a new IOBuf chain sharing the same data as this chain.
965 * The new IOBuf chain will normally point to the same underlying data
966 * buffers as the original chain. (The one exception to this is if some of
967 * the IOBufs in this chain contain small internal data buffers which cannot
970 std::unique_ptr<IOBuf> clone() const;
973 * Return a new IOBuf with the same data as this IOBuf.
975 * The new IOBuf returned will not be part of a chain (even if this IOBuf is
976 * part of a larger chain).
978 std::unique_ptr<IOBuf> cloneOne() const;
981 * Return an iovector suitable for e.g. writev()
983 * auto iov = buf->getIov();
984 * auto xfer = writev(fd, iov.data(), iov.size());
986 * Naturally, the returned iovector is invalid if you modify the buffer
989 folly::fbvector<struct iovec> getIov() const;
992 * Overridden operator new and delete.
993 * These perform specialized memory management to help support
994 * createCombined(), which allocates IOBuf objects together with the buffer
997 void* operator new(size_t size);
998 void* operator new(size_t size, void* ptr);
999 void operator delete(void* ptr);
1002 * Destructively convert this IOBuf to a fbstring efficiently.
1003 * We rely on fbstring's AcquireMallocatedString constructor to
1006 fbstring moveToFbString();
1009 * Iteration support: a chain of IOBufs may be iterated through using
1010 * STL-style iterators over const ByteRanges. Iterators are only invalidated
1011 * if the IOBuf that they currently point to is removed.
1013 Iterator cbegin() const;
1014 Iterator cend() const;
1015 Iterator begin() const;
1016 Iterator end() const;
1019 enum FlagsEnum : uint32_t {
1020 kFlagUserOwned = 0x1,
1021 kFlagFreeSharedInfo = 0x2,
1022 kFlagMaybeShared = 0x4,
1025 // Values for the type_ field.
1026 // We currently don't really use this for anything, other than to have it
1027 // around for debugging purposes. We store it at the moment just because we
1028 // have the 4 extra bytes that would just be padding otherwise.
1029 enum ExtBufTypeEnum {
1031 kExtUserSupplied = 1,
1038 SharedInfo(FreeFunction fn, void* arg);
1040 // A pointer to a function to call to free the buffer when the refcount
1041 // hits 0. If this is NULL, free() will be used instead.
1042 FreeFunction freeFn;
1044 std::atomic<uint32_t> refcount;
1046 // Helper structs for use by operator new and delete
1049 struct HeapFullStorage;
1051 // Forbidden copy constructor and assignment opererator
1052 IOBuf(IOBuf const &);
1053 IOBuf& operator=(IOBuf const &);
1056 * Create a new IOBuf pointing to an external buffer.
1058 * The caller is responsible for holding a reference count for this new
1059 * IOBuf. The IOBuf constructor does not automatically increment the
1062 IOBuf(ExtBufTypeEnum type, uint32_t flags,
1063 uint8_t* buf, uint32_t capacity,
1064 uint8_t* data, uint32_t length,
1065 SharedInfo* sharedInfo);
1067 void unshareOneSlow();
1068 void unshareChained();
1069 void coalesceSlow(size_t maxLength=std::numeric_limits<size_t>::max());
1070 // newLength must be the entire length of the buffers between this and
1071 // end (no truncation)
1072 void coalesceAndReallocate(
1076 size_t newTailroom);
1077 void decrementRefcount();
1078 void reserveSlow(uint32_t minHeadroom, uint32_t minTailroom);
1079 void freeExtBuffer();
1081 static size_t goodExtBufferSize(uint32_t minCapacity);
1082 static void initExtBuffer(uint8_t* buf, size_t mallocSize,
1083 SharedInfo** infoReturn,
1084 uint32_t* capacityReturn);
1085 static void allocExtBuffer(uint32_t minCapacity,
1086 uint8_t** bufReturn,
1087 SharedInfo** infoReturn,
1088 uint32_t* capacityReturn);
1089 static void releaseStorage(HeapStorage* storage, uint16_t freeFlags);
1090 static void freeInternalBuf(void* buf, void* userData);
1097 * Links to the next and the previous IOBuf in this chain.
1099 * The chain is circularly linked (the last element in the chain points back
1100 * at the head), and next_ and prev_ can never be NULL. If this IOBuf is the
1101 * only element in the chain, next_ and prev_ will both point to this.
1107 * A pointer to the start of the data referenced by this IOBuf, and the
1108 * length of the data.
1110 * This may refer to any subsection of the actual buffer capacity.
1116 mutable uint32_t flags_;
1118 // SharedInfo may be NULL if kFlagUserOwned is set. It is non-NULL
1119 // in all other cases.
1120 SharedInfo* sharedInfo_;
1122 struct DeleterBase {
1123 virtual ~DeleterBase() { }
1124 virtual void dispose(void* p) = 0;
1127 template <class UniquePtr>
1128 struct UniquePtrDeleter : public DeleterBase {
1129 typedef typename UniquePtr::pointer Pointer;
1130 typedef typename UniquePtr::deleter_type Deleter;
1132 explicit UniquePtrDeleter(Deleter deleter) : deleter_(std::move(deleter)){ }
1133 void dispose(void* p) {
1135 deleter_(static_cast<Pointer>(p));
1146 static void freeUniquePtrBuffer(void* ptr, void* userData) {
1147 static_cast<DeleterBase*>(userData)->dispose(ptr);
1151 template <class UniquePtr>
1152 typename std::enable_if<detail::IsUniquePtrToSL<UniquePtr>::value,
1153 std::unique_ptr<IOBuf>>::type
1154 IOBuf::takeOwnership(UniquePtr&& buf, size_t count) {
1155 size_t size = count * sizeof(typename UniquePtr::element_type);
1156 DCHECK_LT(size, size_t(std::numeric_limits<uint32_t>::max()));
1157 auto deleter = new UniquePtrDeleter<UniquePtr>(buf.get_deleter());
1158 return takeOwnership(buf.release(),
1160 &IOBuf::freeUniquePtrBuffer,
1164 inline std::unique_ptr<IOBuf> IOBuf::copyBuffer(
1165 const void* data, uint32_t size, uint32_t headroom,
1166 uint32_t minTailroom) {
1167 uint32_t capacity = headroom + size + minTailroom;
1168 std::unique_ptr<IOBuf> buf = create(capacity);
1169 buf->advance(headroom);
1170 memcpy(buf->writableData(), data, size);
1175 inline std::unique_ptr<IOBuf> IOBuf::copyBuffer(const std::string& buf,
1177 uint32_t minTailroom) {
1178 return copyBuffer(buf.data(), buf.size(), headroom, minTailroom);
1181 inline std::unique_ptr<IOBuf> IOBuf::maybeCopyBuffer(const std::string& buf,
1183 uint32_t minTailroom) {
1187 return copyBuffer(buf.data(), buf.size(), headroom, minTailroom);
1190 class IOBuf::Iterator : public boost::iterator_facade<
1191 IOBuf::Iterator, // Derived
1192 const ByteRange, // Value
1193 boost::forward_traversal_tag // Category or traversal
1195 friend class boost::iterator_core_access;
1197 // Note that IOBufs are stored as a circular list without a guard node,
1198 // so pos == end is ambiguous (it may mean "begin" or "end"). To solve
1199 // the ambiguity (at the cost of one extra comparison in the "increment"
1200 // code path), we define end iterators as having pos_ == end_ == nullptr
1201 // and we only allow forward iteration.
1202 explicit Iterator(const IOBuf* pos, const IOBuf* end)
1205 // Sadly, we must return by const reference, not by value.
1213 val_ = ByteRange(pos_->data(), pos_->tail());
1216 void adjustForEnd() {
1218 pos_ = end_ = nullptr;
1225 const ByteRange& dereference() const {
1229 bool equal(const Iterator& other) const {
1230 // We must compare end_ in addition to pos_, because forward traversal
1231 // requires that if two iterators are equal (a == b) and dereferenceable,
1233 return pos_ == other.pos_ && end_ == other.end_;
1237 pos_ = pos_->next();
1246 inline IOBuf::Iterator IOBuf::begin() const { return cbegin(); }
1247 inline IOBuf::Iterator IOBuf::end() const { return cend(); }
1251 #pragma GCC diagnostic pop
1253 #endif // FOLLY_IO_IOBUF_H_