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 * Allocate a new IOBuf chain with the requested total capacity, allocating
227 * no more than maxBufCapacity to each buffer.
229 static std::unique_ptr<IOBuf> createChain(
230 size_t totalCapacity, uint32_t maxBufCapacity);
233 * Create a new IOBuf pointing to an existing data buffer.
235 * The new IOBuffer will assume ownership of the buffer, and free it by
236 * calling the specified FreeFunction when the last IOBuf pointing to this
237 * buffer is destroyed. The function will be called with a pointer to the
238 * buffer as the first argument, and the supplied userData value as the
239 * second argument. The free function must never throw exceptions.
241 * If no FreeFunction is specified, the buffer will be freed using free()
242 * which will result in undefined behavior if the memory was allocated
245 * The IOBuf data pointer will initially point to the start of the buffer,
247 * In the first version of this function, the length of data is unspecified
248 * and is initialized to the capacity of the buffer
250 * In the second version, the user specifies the valid length of data
253 * On error, std::bad_alloc will be thrown. If freeOnError is true (the
254 * default) the buffer will be freed before throwing the error.
256 static std::unique_ptr<IOBuf> takeOwnership(void* buf, uint32_t capacity,
257 FreeFunction freeFn = NULL,
258 void* userData = NULL,
259 bool freeOnError = true) {
260 return takeOwnership(buf, capacity, capacity, freeFn,
261 userData, freeOnError);
264 static std::unique_ptr<IOBuf> takeOwnership(void* buf, uint32_t capacity,
266 FreeFunction freeFn = NULL,
267 void* userData = NULL,
268 bool freeOnError = true);
271 * Create a new IOBuf pointing to an existing data buffer made up of
272 * count objects of a given standard-layout type.
274 * This is dangerous -- it is essentially equivalent to doing
275 * reinterpret_cast<unsigned char*> on your data -- but it's often useful
276 * for serialization / deserialization.
278 * The new IOBuffer will assume ownership of the buffer, and free it
279 * appropriately (by calling the UniquePtr's custom deleter, or by calling
280 * delete or delete[] appropriately if there is no custom deleter)
281 * when the buffer is destroyed. The custom deleter, if any, must never
284 * The IOBuf data pointer will initially point to the start of the buffer,
285 * and the length will be the full capacity of the buffer (count *
288 * On error, std::bad_alloc will be thrown, and the buffer will be freed
289 * before throwing the error.
291 template <class UniquePtr>
292 static typename std::enable_if<detail::IsUniquePtrToSL<UniquePtr>::value,
293 std::unique_ptr<IOBuf>>::type
294 takeOwnership(UniquePtr&& buf, size_t count=1);
297 * Create a new IOBuf object that points to an existing user-owned buffer.
299 * This should only be used when the caller knows the lifetime of the IOBuf
300 * object ahead of time and can ensure that all IOBuf objects that will point
301 * to this buffer will be destroyed before the buffer itself is destroyed.
303 * This buffer will not be freed automatically when the last IOBuf
304 * referencing it is destroyed. It is the caller's responsibility to free
305 * the buffer after the last IOBuf has been destroyed.
307 * The IOBuf data pointer will initially point to the start of the buffer,
308 * and the length will be the full capacity of the buffer.
310 * An IOBuf created using wrapBuffer() will always be reported as shared.
311 * unshare() may be used to create a writable copy of the buffer.
313 * On error, std::bad_alloc will be thrown.
315 static std::unique_ptr<IOBuf> wrapBuffer(const void* buf, uint32_t capacity);
318 * Convenience function to create a new IOBuf object that copies data from a
319 * user-supplied buffer, optionally allocating a given amount of
320 * headroom and tailroom.
322 static std::unique_ptr<IOBuf> copyBuffer(const void* buf, uint32_t size,
324 uint32_t minTailroom=0);
327 * Convenience function to create a new IOBuf object that copies data from a
328 * user-supplied string, optionally allocating a given amount of
329 * headroom and tailroom.
331 * Beware when attempting to invoke this function with a constant string
332 * literal and a headroom argument: you will likely end up invoking the
333 * version of copyBuffer() above. IOBuf::copyBuffer("hello", 3) will treat
334 * the first argument as a const void*, and will invoke the version of
335 * copyBuffer() above, with the size argument of 3.
337 static std::unique_ptr<IOBuf> copyBuffer(const std::string& buf,
339 uint32_t minTailroom=0);
342 * A version of copyBuffer() that returns a null pointer if the input string
345 static std::unique_ptr<IOBuf> maybeCopyBuffer(const std::string& buf,
347 uint32_t minTailroom=0);
350 * Convenience function to free a chain of IOBufs held by a unique_ptr.
352 static void destroy(std::unique_ptr<IOBuf>&& data) {
353 auto destroyer = std::move(data);
357 * Destroy this IOBuf.
359 * Deleting an IOBuf will automatically destroy all IOBufs in the chain.
360 * (See the comments above regarding the ownership model of IOBuf chains.
361 * All subsequent IOBufs in the chain are considered to be owned by the head
362 * of the chain. Users should only explicitly delete the head of a chain.)
364 * When each individual IOBuf is destroyed, it will release its reference
365 * count on the underlying buffer. If it was the last user of the buffer,
366 * the buffer will be freed.
371 * Check whether the chain is empty (i.e., whether the IOBufs in the
372 * chain have a total data length of zero).
374 * This method is semantically equivalent to
375 * i->computeChainDataLength()==0
376 * but may run faster because it can short-circuit as soon as it
377 * encounters a buffer with length()!=0
382 * Get the pointer to the start of the data.
384 const uint8_t* data() const {
389 * Get a writable pointer to the start of the data.
391 * The caller is responsible for calling unshare() first to ensure that it is
392 * actually safe to write to the buffer.
394 uint8_t* writableData() {
399 * Get the pointer to the end of the data.
401 const uint8_t* tail() const {
402 return data_ + length_;
406 * Get a writable pointer to the end of the data.
408 * The caller is responsible for calling unshare() first to ensure that it is
409 * actually safe to write to the buffer.
411 uint8_t* writableTail() {
412 return data_ + length_;
416 * Get the data length.
418 uint32_t length() const {
423 * Get the amount of head room.
425 * Returns the number of bytes in the buffer before the start of the data.
427 uint32_t headroom() const {
428 return data_ - buffer();
432 * Get the amount of tail room.
434 * Returns the number of bytes in the buffer after the end of the data.
436 uint32_t tailroom() const {
437 return bufferEnd() - tail();
441 * Get the pointer to the start of the buffer.
443 * Note that this is the pointer to the very beginning of the usable buffer,
444 * not the start of valid data within the buffer. Use the data() method to
445 * get a pointer to the start of the data within the buffer.
447 const uint8_t* buffer() const {
448 return (flags_ & kFlagExt) ? ext_.buf : int_.buf;
452 * Get a writable pointer to the start of the buffer.
454 * The caller is responsible for calling unshare() first to ensure that it is
455 * actually safe to write to the buffer.
457 uint8_t* writableBuffer() {
458 return (flags_ & kFlagExt) ? ext_.buf : int_.buf;
462 * Get the pointer to the end of the buffer.
464 * Note that this is the pointer to the very end of the usable buffer,
465 * not the end of valid data within the buffer. Use the tail() method to
466 * get a pointer to the end of the data within the buffer.
468 const uint8_t* bufferEnd() const {
469 return (flags_ & kFlagExt) ?
470 ext_.buf + ext_.capacity :
471 int_.buf + kMaxInternalDataSize;
475 * Get the total size of the buffer.
477 * This returns the total usable length of the buffer. Use the length()
478 * method to get the length of the actual valid data in this IOBuf.
480 uint32_t capacity() const {
481 return (flags_ & kFlagExt) ? ext_.capacity : kMaxInternalDataSize;
485 * Get a pointer to the next IOBuf in this chain.
490 const IOBuf* next() const {
495 * Get a pointer to the previous IOBuf in this chain.
500 const IOBuf* prev() const {
505 * Shift the data forwards in the buffer.
507 * This shifts the data pointer forwards in the buffer to increase the
508 * headroom. This is commonly used to increase the headroom in a newly
511 * The caller is responsible for ensuring that there is sufficient
512 * tailroom in the buffer before calling advance().
514 * If there is a non-zero data length, advance() will use memmove() to shift
515 * the data forwards in the buffer. In this case, the caller is responsible
516 * for making sure the buffer is unshared, so it will not affect other IOBufs
517 * that may be sharing the same underlying buffer.
519 void advance(uint32_t amount) {
520 // In debug builds, assert if there is a problem.
521 assert(amount <= tailroom());
524 memmove(data_ + amount, data_, length_);
530 * Shift the data backwards in the buffer.
532 * The caller is responsible for ensuring that there is sufficient headroom
533 * in the buffer before calling retreat().
535 * If there is a non-zero data length, retreat() will use memmove() to shift
536 * the data backwards in the buffer. In this case, the caller is responsible
537 * for making sure the buffer is unshared, so it will not affect other IOBufs
538 * that may be sharing the same underlying buffer.
540 void retreat(uint32_t amount) {
541 // In debug builds, assert if there is a problem.
542 assert(amount <= headroom());
545 memmove(data_ - amount, data_, length_);
551 * Adjust the data pointer to include more valid data at the beginning.
553 * This moves the data pointer backwards to include more of the available
554 * buffer. The caller is responsible for ensuring that there is sufficient
555 * headroom for the new data. The caller is also responsible for populating
556 * this section with valid data.
558 * This does not modify any actual data in the buffer.
560 void prepend(uint32_t amount) {
561 DCHECK_LE(amount, headroom());
567 * Adjust the tail pointer to include more valid data at the end.
569 * This moves the tail pointer forwards to include more of the available
570 * buffer. The caller is responsible for ensuring that there is sufficient
571 * tailroom for the new data. The caller is also responsible for populating
572 * this section with valid data.
574 * This does not modify any actual data in the buffer.
576 void append(uint32_t amount) {
577 DCHECK_LE(amount, tailroom());
582 * Adjust the data pointer forwards to include less valid data.
584 * This moves the data pointer forwards so that the first amount bytes are no
585 * longer considered valid data. The caller is responsible for ensuring that
586 * amount is less than or equal to the actual data length.
588 * This does not modify any actual data in the buffer.
590 void trimStart(uint32_t amount) {
591 DCHECK_LE(amount, length_);
597 * Adjust the tail pointer backwards to include less valid data.
599 * This moves the tail pointer backwards so that the last amount bytes are no
600 * longer considered valid data. The caller is responsible for ensuring that
601 * amount is less than or equal to the actual data length.
603 * This does not modify any actual data in the buffer.
605 void trimEnd(uint32_t amount) {
606 DCHECK_LE(amount, length_);
613 * Postcondition: headroom() == 0, length() == 0, tailroom() == capacity()
616 data_ = writableBuffer();
621 * Ensure that this buffer has at least minHeadroom headroom bytes and at
622 * least minTailroom tailroom bytes. The buffer must be writable
623 * (you must call unshare() before this, if necessary).
625 * Postcondition: headroom() >= minHeadroom, tailroom() >= minTailroom,
626 * the data (between data() and data() + length()) is preserved.
628 void reserve(uint32_t minHeadroom, uint32_t minTailroom) {
629 // Maybe we don't need to do anything.
630 if (headroom() >= minHeadroom && tailroom() >= minTailroom) {
633 // If the buffer is empty but we have enough total room (head + tail),
634 // move the data_ pointer around.
636 headroom() + tailroom() >= minHeadroom + minTailroom) {
637 data_ = writableBuffer() + minHeadroom;
640 // Bah, we have to do actual work.
641 reserveSlow(minHeadroom, minTailroom);
645 * Return true if this IOBuf is part of a chain of multiple IOBufs, or false
646 * if this is the only IOBuf in its chain.
648 bool isChained() const {
649 assert((next_ == this) == (prev_ == this));
650 return next_ != this;
654 * Get the number of IOBufs in this chain.
656 * Beware that this method has to walk the entire chain.
657 * Use isChained() if you just want to check if this IOBuf is part of a chain
660 uint32_t countChainElements() const;
663 * Get the length of all the data in this IOBuf chain.
665 * Beware that this method has to walk the entire chain.
667 uint64_t computeChainDataLength() const;
670 * Insert another IOBuf chain immediately before this IOBuf.
672 * For example, if there are two IOBuf chains (A, B, C) and (D, E, F),
673 * and B->prependChain(D) is called, the (D, E, F) chain will be subsumed
674 * and become part of the chain starting at A, which will now look like
677 * Note that since IOBuf chains are circular, head->prependChain(other) can
678 * be used to append the other chain at the very end of the chain pointed to
679 * by head. For example, if there are two IOBuf chains (A, B, C) and
680 * (D, E, F), and A->prependChain(D) is called, the chain starting at A will
681 * now consist of (A, B, C, D, E, F)
683 * The elements in the specified IOBuf chain will become part of this chain,
684 * and will be owned by the head of this chain. When this chain is
685 * destroyed, all elements in the supplied chain will also be destroyed.
687 * For this reason, appendChain() only accepts an rvalue-reference to a
688 * unique_ptr(), to make it clear that it is taking ownership of the supplied
689 * chain. If you have a raw pointer, you can pass in a new temporary
690 * unique_ptr around the raw pointer. If you have an existing,
691 * non-temporary unique_ptr, you must call std::move(ptr) to make it clear
692 * that you are destroying the original pointer.
694 void prependChain(std::unique_ptr<IOBuf>&& iobuf);
697 * Append another IOBuf chain immediately after this IOBuf.
699 * For example, if there are two IOBuf chains (A, B, C) and (D, E, F),
700 * and B->appendChain(D) is called, the (D, E, F) chain will be subsumed
701 * and become part of the chain starting at A, which will now look like
704 * The elements in the specified IOBuf chain will become part of this chain,
705 * and will be owned by the head of this chain. When this chain is
706 * destroyed, all elements in the supplied chain will also be destroyed.
708 * For this reason, appendChain() only accepts an rvalue-reference to a
709 * unique_ptr(), to make it clear that it is taking ownership of the supplied
710 * chain. If you have a raw pointer, you can pass in a new temporary
711 * unique_ptr around the raw pointer. If you have an existing,
712 * non-temporary unique_ptr, you must call std::move(ptr) to make it clear
713 * that you are destroying the original pointer.
715 void appendChain(std::unique_ptr<IOBuf>&& iobuf) {
716 // Just use prependChain() on the next element in our chain
717 next_->prependChain(std::move(iobuf));
721 * Remove this IOBuf from its current chain.
723 * Since ownership of all elements an IOBuf chain is normally maintained by
724 * the head of the chain, unlink() transfers ownership of this IOBuf from the
725 * chain and gives it to the caller. A new unique_ptr to the IOBuf is
726 * returned to the caller. The caller must store the returned unique_ptr (or
727 * call release() on it) to take ownership, otherwise the IOBuf will be
728 * immediately destroyed.
730 * Since unlink transfers ownership of the IOBuf to the caller, be careful
731 * not to call unlink() on the head of a chain if you already maintain
732 * ownership on the head of the chain via other means. The pop() method
733 * is a better choice for that situation.
735 std::unique_ptr<IOBuf> unlink() {
736 next_->prev_ = prev_;
737 prev_->next_ = next_;
740 return std::unique_ptr<IOBuf>(this);
744 * Remove this IOBuf from its current chain and return a unique_ptr to
745 * the IOBuf that formerly followed it in the chain.
747 std::unique_ptr<IOBuf> pop() {
749 next_->prev_ = prev_;
750 prev_->next_ = next_;
753 return std::unique_ptr<IOBuf>((next == this) ? NULL : next);
757 * Remove a subchain from this chain.
759 * Remove the subchain starting at head and ending at tail from this chain.
761 * Returns a unique_ptr pointing to head. (In other words, ownership of the
762 * head of the subchain is transferred to the caller.) If the caller ignores
763 * the return value and lets the unique_ptr be destroyed, the subchain will
764 * be immediately destroyed.
766 * The subchain referenced by the specified head and tail must be part of the
767 * same chain as the current IOBuf, but must not contain the current IOBuf.
768 * However, the specified head and tail may be equal to each other (i.e.,
769 * they may be a subchain of length 1).
771 std::unique_ptr<IOBuf> separateChain(IOBuf* head, IOBuf* tail) {
772 assert(head != this);
773 assert(tail != this);
775 head->prev_->next_ = tail->next_;
776 tail->next_->prev_ = head->prev_;
781 return std::unique_ptr<IOBuf>(head);
785 * Return true if at least one of the IOBufs in this chain are shared,
786 * or false if all of the IOBufs point to unique buffers.
788 * Use isSharedOne() to only check this IOBuf rather than the entire chain.
790 bool isShared() const {
791 const IOBuf* current = this;
793 if (current->isSharedOne()) {
796 current = current->next_;
797 if (current == this) {
804 * Return true if other IOBufs are also pointing to the buffer used by this
805 * IOBuf, and false otherwise.
807 * If this IOBuf points at a buffer owned by another (non-IOBuf) part of the
808 * code (i.e., if the IOBuf was created using wrapBuffer(), or was cloned
809 * from such an IOBuf), it is always considered shared.
811 * This only checks the current IOBuf, and not other IOBufs in the chain.
813 bool isSharedOne() const {
814 if (LIKELY(flags_ & (kFlagUserOwned | kFlagMaybeShared)) == 0) {
818 // If this is a user-owned buffer, it is always considered shared
819 if (flags_ & kFlagUserOwned) {
823 // an internal buffer wouldn't have kFlagMaybeShared or kFlagUserOwned
824 // so we would have returned false already. The only remaining case
825 // is an external buffer which may be shared, so we need to read
826 // the reference count.
827 assert((flags_ & (kFlagExt | kFlagMaybeShared)) ==
828 (kFlagExt | kFlagMaybeShared));
831 ext_.sharedInfo->refcount.load(std::memory_order_acquire) > 1;
833 // we're the last one left
834 flags_ &= ~kFlagMaybeShared;
840 * Ensure that this IOBuf has a unique buffer that is not shared by other
843 * unshare() operates on an entire chain of IOBuf objects. If the chain is
844 * shared, it may also coalesce the chain when making it unique. If the
845 * chain is coalesced, subsequent IOBuf objects in the current chain will be
846 * automatically deleted.
848 * Note that buffers owned by other (non-IOBuf) users are automatically
851 * Throws std::bad_alloc on error. On error the IOBuf chain will be
854 * Currently unshare may also throw std::overflow_error if it tries to
855 * coalesce. (TODO: In the future it would be nice if unshare() were smart
856 * enough not to coalesce the entire buffer if the data is too large.
857 * However, in practice this seems unlikely to become an issue.)
868 * Ensure that this IOBuf has a unique buffer that is not shared by other
871 * unshareOne() operates on a single IOBuf object. This IOBuf will have a
872 * unique buffer after unshareOne() returns, but other IOBufs in the chain
873 * may still be shared after unshareOne() returns.
875 * Throws std::bad_alloc on error. On error the IOBuf will be unmodified.
884 * Coalesce this IOBuf chain into a single buffer.
886 * This method moves all of the data in this IOBuf chain into a single
887 * contiguous buffer, if it is not already in one buffer. After coalesce()
888 * returns, this IOBuf will be a chain of length one. Other IOBufs in the
889 * chain will be automatically deleted.
891 * After coalescing, the IOBuf will have at least as much headroom as the
892 * first IOBuf in the chain, and at least as much tailroom as the last IOBuf
895 * Throws std::bad_alloc on error. On error the IOBuf chain will be
896 * unmodified. Throws std::overflow_error if the length of the entire chain
897 * larger than can be described by a uint32_t capacity.
907 * Ensure that this chain has at least maxLength bytes available as a
908 * contiguous memory range.
910 * This method coalesces whole buffers in the chain into this buffer as
911 * necessary until this buffer's length() is at least maxLength.
913 * After coalescing, the IOBuf will have at least as much headroom as the
914 * first IOBuf in the chain, and at least as much tailroom as the last IOBuf
915 * that was coalesced.
917 * Throws std::bad_alloc on error. On error the IOBuf chain will be
918 * unmodified. Throws std::overflow_error if the length of the coalesced
919 * portion of the chain is larger than can be described by a uint32_t
920 * capacity. (Although maxLength is uint32_t, gather() doesn't split
921 * buffers, so coalescing whole buffers may result in a capacity that can't
922 * be described in uint32_t.
924 * Upon return, either enough of the chain was coalesced into a contiguous
925 * region, or the entire chain was coalesced. That is,
926 * length() >= maxLength || !isChained() is true.
928 void gather(uint32_t maxLength) {
929 if (!isChained() || length_ >= maxLength) {
932 coalesceSlow(maxLength);
936 * Return a new IOBuf chain sharing the same data as this chain.
938 * The new IOBuf chain will normally point to the same underlying data
939 * buffers as the original chain. (The one exception to this is if some of
940 * the IOBufs in this chain contain small internal data buffers which cannot
943 std::unique_ptr<IOBuf> clone() const;
946 * Return a new IOBuf with the same data as this IOBuf.
948 * The new IOBuf returned will not be part of a chain (even if this IOBuf is
949 * part of a larger chain).
951 std::unique_ptr<IOBuf> cloneOne() const;
954 * Return an iovector suitable for e.g. writev()
956 * auto iov = buf->getIov();
957 * auto xfer = writev(fd, iov.data(), iov.size());
959 * Naturally, the returned iovector is invalid if you modify the buffer
962 folly::fbvector<struct iovec> getIov() const;
964 // Overridden operator new and delete.
965 // These directly use malloc() and free() to allocate the space for IOBuf
966 // objects. This is needed since IOBuf::create() manually uses malloc when
967 // allocating IOBuf objects with an internal buffer.
968 void* operator new(size_t size);
969 void* operator new(size_t size, void* ptr);
970 void operator delete(void* ptr);
973 * Destructively convert this IOBuf to a fbstring efficiently.
974 * We rely on fbstring's AcquireMallocatedString constructor to
977 fbstring moveToFbString();
980 * Iteration support: a chain of IOBufs may be iterated through using
981 * STL-style iterators over const ByteRanges. Iterators are only invalidated
982 * if the IOBuf that they currently point to is removed.
984 Iterator cbegin() const;
985 Iterator cend() const;
986 Iterator begin() const;
987 Iterator end() const;
990 enum FlagsEnum : uint32_t {
992 kFlagUserOwned = 0x2,
993 kFlagFreeSharedInfo = 0x4,
994 kFlagMaybeShared = 0x8,
997 // Values for the ExternalBuf type field.
998 // We currently don't really use this for anything, other than to have it
999 // around for debugging purposes. We store it at the moment just because we
1000 // have the 4 extra bytes in the ExternalBuf struct that would just be
1001 // padding otherwise.
1002 enum ExtBufTypeEnum {
1004 kExtUserSupplied = 1,
1010 SharedInfo(FreeFunction fn, void* arg);
1012 // A pointer to a function to call to free the buffer when the refcount
1013 // hits 0. If this is NULL, free() will be used instead.
1014 FreeFunction freeFn;
1016 std::atomic<uint32_t> refcount;
1018 struct ExternalBuf {
1022 // SharedInfo may be NULL if kFlagUserOwned is set. It is non-NULL
1023 // in all other cases.
1024 SharedInfo* sharedInfo;
1026 struct InternalBuf {
1027 uint8_t buf[] __attribute__((aligned));
1030 // The maximum size for an IOBuf object, including any internal data buffer
1031 static const uint32_t kMaxIOBufSize = 256;
1032 static const uint32_t kMaxInternalDataSize;
1034 // Forbidden copy constructor and assignment opererator
1035 IOBuf(IOBuf const &);
1036 IOBuf& operator=(IOBuf const &);
1039 * Create a new IOBuf with internal data.
1041 * end is a pointer to the end of the IOBuf's internal data buffer.
1043 explicit IOBuf(uint8_t* end);
1046 * Create a new IOBuf pointing to an external buffer.
1048 * The caller is responsible for holding a reference count for this new
1049 * IOBuf. The IOBuf constructor does not automatically increment the
1052 IOBuf(ExtBufTypeEnum type, uint32_t flags,
1053 uint8_t* buf, uint32_t capacity,
1054 uint8_t* data, uint32_t length,
1055 SharedInfo* sharedInfo);
1057 void unshareOneSlow();
1058 void unshareChained();
1059 void coalesceSlow(size_t maxLength=std::numeric_limits<size_t>::max());
1060 // newLength must be the entire length of the buffers between this and
1061 // end (no truncation)
1062 void coalesceAndReallocate(
1066 size_t newTailroom);
1067 void decrementRefcount();
1068 void reserveSlow(uint32_t minHeadroom, uint32_t minTailroom);
1070 static size_t goodExtBufferSize(uint32_t minCapacity);
1071 static void initExtBuffer(uint8_t* buf, size_t mallocSize,
1072 SharedInfo** infoReturn,
1073 uint32_t* capacityReturn);
1074 static void allocExtBuffer(uint32_t minCapacity,
1075 uint8_t** bufReturn,
1076 SharedInfo** infoReturn,
1077 uint32_t* capacityReturn);
1084 * Links to the next and the previous IOBuf in this chain.
1086 * The chain is circularly linked (the last element in the chain points back
1087 * at the head), and next_ and prev_ can never be NULL. If this IOBuf is the
1088 * only element in the chain, next_ and prev_ will both point to this.
1094 * A pointer to the start of the data referenced by this IOBuf, and the
1095 * length of the data.
1097 * This may refer to any subsection of the actual buffer capacity.
1101 mutable uint32_t flags_;
1108 struct DeleterBase {
1109 virtual ~DeleterBase() { }
1110 virtual void dispose(void* p) = 0;
1113 template <class UniquePtr>
1114 struct UniquePtrDeleter : public DeleterBase {
1115 typedef typename UniquePtr::pointer Pointer;
1116 typedef typename UniquePtr::deleter_type Deleter;
1118 explicit UniquePtrDeleter(Deleter deleter) : deleter_(std::move(deleter)){ }
1119 void dispose(void* p) {
1121 deleter_(static_cast<Pointer>(p));
1132 static void freeUniquePtrBuffer(void* ptr, void* userData) {
1133 static_cast<DeleterBase*>(userData)->dispose(ptr);
1137 template <class UniquePtr>
1138 typename std::enable_if<detail::IsUniquePtrToSL<UniquePtr>::value,
1139 std::unique_ptr<IOBuf>>::type
1140 IOBuf::takeOwnership(UniquePtr&& buf, size_t count) {
1141 size_t size = count * sizeof(typename UniquePtr::element_type);
1142 DCHECK_LT(size, size_t(std::numeric_limits<uint32_t>::max()));
1143 auto deleter = new UniquePtrDeleter<UniquePtr>(buf.get_deleter());
1144 return takeOwnership(buf.release(),
1146 &IOBuf::freeUniquePtrBuffer,
1150 inline std::unique_ptr<IOBuf> IOBuf::copyBuffer(
1151 const void* data, uint32_t size, uint32_t headroom,
1152 uint32_t minTailroom) {
1153 uint32_t capacity = headroom + size + minTailroom;
1154 std::unique_ptr<IOBuf> buf = create(capacity);
1155 buf->advance(headroom);
1156 memcpy(buf->writableData(), data, size);
1161 inline std::unique_ptr<IOBuf> IOBuf::copyBuffer(const std::string& buf,
1163 uint32_t minTailroom) {
1164 return copyBuffer(buf.data(), buf.size(), headroom, minTailroom);
1167 inline std::unique_ptr<IOBuf> IOBuf::maybeCopyBuffer(const std::string& buf,
1169 uint32_t minTailroom) {
1173 return copyBuffer(buf.data(), buf.size(), headroom, minTailroom);
1176 class IOBuf::Iterator : public boost::iterator_facade<
1177 IOBuf::Iterator, // Derived
1178 const ByteRange, // Value
1179 boost::forward_traversal_tag // Category or traversal
1181 friend class boost::iterator_core_access;
1183 // Note that IOBufs are stored as a circular list without a guard node,
1184 // so pos == end is ambiguous (it may mean "begin" or "end"). To solve
1185 // the ambiguity (at the cost of one extra comparison in the "increment"
1186 // code path), we define end iterators as having pos_ == end_ == nullptr
1187 // and we only allow forward iteration.
1188 explicit Iterator(const IOBuf* pos, const IOBuf* end)
1191 // Sadly, we must return by const reference, not by value.
1199 val_ = ByteRange(pos_->data(), pos_->tail());
1202 void adjustForEnd() {
1204 pos_ = end_ = nullptr;
1211 const ByteRange& dereference() const {
1215 bool equal(const Iterator& other) const {
1216 // We must compare end_ in addition to pos_, because forward traversal
1217 // requires that if two iterators are equal (a == b) and dereferenceable,
1219 return pos_ == other.pos_ && end_ == other.end_;
1223 pos_ = pos_->next();
1232 inline IOBuf::Iterator IOBuf::begin() const { return cbegin(); }
1233 inline IOBuf::Iterator IOBuf::end() const { return cend(); }
1237 #pragma GCC diagnostic pop
1239 #endif // FOLLY_IO_IOBUF_H_