2 * Copyright 2012 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>
28 #include <type_traits>
30 #include "folly/FBString.h"
35 * An IOBuf is a pointer to a buffer of data.
37 * IOBuf objects are intended to be used primarily for networking code, and are
38 * modelled somewhat after FreeBSD's mbuf data structure, and Linux's sk_buff
41 * IOBuf objects facilitate zero-copy network programming, by allowing multiple
42 * IOBuf objects to point to the same underlying buffer of data, using a
43 * reference count to track when the buffer is no longer needed and can be
50 * The IOBuf itself is a small object containing a pointer to the buffer and
51 * information about which segment of the buffer contains valid data.
53 * The data layout looks like this:
61 * +------------+--------------------+-----------+
62 * | headroom | data | tailroom |
63 * +------------+--------------------+-----------+
65 * buffer() data() tail() bufferEnd()
67 * The length() method returns the length of the valid data; capacity()
68 * returns the entire capacity of the buffer (from buffer() to bufferEnd()).
69 * The headroom() and tailroom() methods return the amount of unused capacity
70 * available before and after the data.
76 * The buffer itself is reference counted, and multiple IOBuf objects may point
77 * to the same buffer. Each IOBuf may point to a different section of valid
78 * data within the underlying buffer. For example, if multiple protocol
79 * requests are read from the network into a single buffer, a separate IOBuf
80 * may be created for each request, all sharing the same underlying buffer.
82 * In other words, when multiple IOBufs share the same underlying buffer, the
83 * data() and tail() methods on each IOBuf may point to a different segment of
84 * the data. However, the buffer() and bufferEnd() methods will point to the
85 * same location for all IOBufs sharing the same underlying buffer.
87 * +-----------+ +---------+
88 * | IOBuf 1 | | IOBuf 2 |
89 * +-----------+ +---------+
91 * data | tail |/ data | tail
93 * +-------------------------------------+
95 * +-------------------------------------+
97 * If you only read data from an IOBuf, you don't need to worry about other
98 * IOBuf objects possibly sharing the same underlying buffer. However, if you
99 * ever write to the buffer you need to first ensure that no other IOBufs point
100 * to the same buffer. The unshare() method may be used to ensure that you
101 * have an unshared buffer.
107 * IOBuf objects also contain pointers to next and previous IOBuf objects.
108 * This can be used to represent a single logical piece of data that its stored
109 * in non-contiguous chunks in separate buffers.
111 * A single IOBuf object can only belong to one chain at a time.
113 * IOBuf chains are always circular. The "prev" pointer in the head of the
114 * chain points to the tail of the chain. However, it is up to the user to
115 * decide which IOBuf is the head. Internally the IOBuf code does not care
116 * which element is the head.
118 * The lifetime of all IOBufs in the chain are linked: when one element in the
119 * chain is deleted, all other chained elements are also deleted. Conceptually
120 * it is simplest to treat this as if the head of the chain owns all other
121 * IOBufs in the chain. When you delete the head of the chain, it will delete
122 * the other elements as well. For this reason, prependChain() and
123 * appendChain() take ownership of of the new elements being added to this
126 * When the coalesce() method is used to coalesce an entire IOBuf chain into a
127 * single IOBuf, all other IOBufs in the chain are eliminated and automatically
128 * deleted. The unshare() method may coalesce the chain; if it does it will
129 * similarly delete all IOBufs eliminated from the chain.
131 * As discussed in the following section, it is up to the user to maintain a
132 * lock around the entire IOBuf chain if multiple threads need to access the
133 * chain. IOBuf does not provide any internal locking.
139 * When used in multithread programs, a single IOBuf object should only be used
140 * in a single thread at a time. If a caller uses a single IOBuf across
141 * multiple threads the caller is responsible for using an external lock to
142 * synchronize access to the IOBuf.
144 * Two separate IOBuf objects may be accessed concurrently in separate threads
145 * without locking, even if they point to the same underlying buffer. The
146 * buffer reference count is always accessed atomically, and no other
147 * operations should affect other IOBufs that point to the same data segment.
148 * The caller is responsible for using unshare() to ensure that the data buffer
149 * is not shared by other IOBufs before writing to it, and this ensures that
150 * the data itself is not modified in one thread while also being accessed from
153 * For IOBuf chains, no two IOBufs in the same chain should be accessed
154 * simultaneously in separate threads. The caller must maintain a lock around
155 * the entire chain if the chain, or individual IOBufs in the chain, may be
156 * accessed by multiple threads.
159 * IOBuf Object Allocation/Sharing
160 * -------------------------------
162 * IOBuf objects themselves are always allocated on the heap. The IOBuf
163 * constructors are private, so IOBuf objects may not be created on the stack.
164 * In part this is done since some IOBuf objects use small-buffer optimization
165 * and contain the buffer data immediately after the IOBuf object itself. The
166 * coalesce() and unshare() methods also expect to be able to delete subsequent
167 * IOBuf objects in the chain if they are no longer needed due to coalescing.
169 * The IOBuf structure also does not provide room for an intrusive refcount on
170 * the IOBuf object itself, only the underlying data buffer is reference
171 * counted. If users want to share the same IOBuf object between multiple
172 * parts of the code, they are responsible for managing this sharing on their
173 * own. (For example, by using a shared_ptr. Alternatively, users always have
174 * the option of using clone() to create a second IOBuf that points to the same
175 * underlying buffer.)
177 * With jemalloc, allocating small objects like IOBuf objects should be
178 * relatively fast, and the cost of allocating IOBuf objects on the heap and
179 * cloning new IOBufs should be relatively cheap.
182 // Is T a unique_ptr<> to a standard-layout type?
183 template <class T, class Enable=void> struct IsUniquePtrToSL
184 : public std::false_type { };
185 template <class T, class D>
186 struct IsUniquePtrToSL<
187 std::unique_ptr<T, D>,
188 typename std::enable_if<std::is_standard_layout<T>::value>::type>
189 : public std::true_type { };
190 } // namespace detail
194 typedef void (*FreeFunction)(void* buf, void* userData);
197 * Allocate a new IOBuf object with the requested capacity.
199 * Returns a new IOBuf object that must be (eventually) deleted by the
200 * caller. The returned IOBuf may actually have slightly more capacity than
203 * The data pointer will initially point to the start of the newly allocated
204 * buffer, and will have a data length of 0.
206 * Throws std::bad_alloc on error.
208 static std::unique_ptr<IOBuf> create(uint32_t capacity);
211 * Create a new IOBuf pointing to an existing data buffer.
213 * The new IOBuffer will assume ownership of the buffer, and free it by
214 * calling the specified FreeFunction when the last IOBuf pointing to this
215 * buffer is destroyed. The function will be called with a pointer to the
216 * buffer as the first argument, and the supplied userData value as the
217 * second argument. The free function must never throw exceptions.
219 * If no FreeFunction is specified, the buffer will be freed using free().
221 * The IOBuf data pointer will initially point to the start of the buffer,
223 * In the first version of this function, the length of data is unspecified
224 * and is initialized to the capacity of the buffer
226 * In the second version, the user specifies the valid length of data
229 * On error, std::bad_alloc will be thrown. If freeOnError is true (the
230 * default) the buffer will be freed before throwing the error.
232 static std::unique_ptr<IOBuf> takeOwnership(void* buf, uint32_t capacity,
233 FreeFunction freeFn = NULL,
234 void* userData = NULL,
235 bool freeOnError = true) {
236 return takeOwnership(buf, capacity, capacity, freeFn,
237 userData, freeOnError);
240 static std::unique_ptr<IOBuf> takeOwnership(void* buf, uint32_t capacity,
242 FreeFunction freeFn = NULL,
243 void* userData = NULL,
244 bool freeOnError = true);
247 * Create a new IOBuf pointing to an existing data buffer made up of
248 * count objects of a given standard-layout type.
250 * This is dangerous -- it is essentially equivalent to doing
251 * reinterpret_cast<unsigned char*> on your data -- but it's often useful
252 * for serialization / deserialization.
254 * The new IOBuffer will assume ownership of the buffer, and free it
255 * appropriately (by calling the UniquePtr's custom deleter, or by calling
256 * delete or delete[] appropriately if there is no custom deleter)
257 * when the buffer is destroyed. The custom deleter, if any, must never
260 * The IOBuf data pointer will initially point to the start of the buffer,
261 * and the length will be the full capacity of the buffer (count *
264 * On error, std::bad_alloc will be thrown, and the buffer will be freed
265 * before throwing the error.
267 template <class UniquePtr>
268 static typename std::enable_if<detail::IsUniquePtrToSL<UniquePtr>::value,
269 std::unique_ptr<IOBuf>>::type
270 takeOwnership(UniquePtr&& buf, size_t count=1);
273 * Create a new IOBuf object that points to an existing user-owned buffer.
275 * This should only be used when the caller knows the lifetime of the IOBuf
276 * object ahead of time and can ensure that all IOBuf objects that will point
277 * to this buffer will be destroyed before the buffer itself is destroyed.
279 * This buffer will not be freed automatically when the last IOBuf
280 * referencing it is destroyed. It is the caller's responsibility to free
281 * the buffer after the last IOBuf has been destroyed.
283 * The IOBuf data pointer will initially point to the start of the buffer,
284 * and the length will be the full capacity of the buffer.
286 * An IOBuf created using wrapBuffer() will always be reported as shared.
287 * unshare() may be used to create a writable copy of the buffer.
289 * On error, std::bad_alloc will be thrown.
291 static std::unique_ptr<IOBuf> wrapBuffer(const void* buf, uint32_t capacity);
294 * Convenience function to create a new IOBuf object that copies data from a
295 * user-supplied buffer, optionally allocating a given amount of
296 * headroom and tailroom.
298 static std::unique_ptr<IOBuf> copyBuffer(const void* buf, uint32_t size,
300 uint32_t minTailroom=0);
303 * Convenience function to free a chain of IOBufs held by a unique_ptr.
305 static void destroy(std::unique_ptr<IOBuf>&& data) {
306 auto destroyer = std::move(data);
310 * Destroy this IOBuf.
312 * Deleting an IOBuf will automatically destroy all IOBufs in the chain.
313 * (See the comments above regarding the ownership model of IOBuf chains.
314 * All subsequent IOBufs in the chain are considered to be owned by the head
315 * of the chain. Users should only explicitly delete the head of a chain.)
317 * When each individual IOBuf is destroyed, it will release its reference
318 * count on the underlying buffer. If it was the last user of the buffer,
319 * the buffer will be freed.
324 * Check whether the chain is empty (i.e., whether the IOBufs in the
325 * chain have a total data length of zero).
327 * This method is semantically equivalent to
328 * i->computeChainDataLength()==0
329 * but may run faster because it can short-circuit as soon as it
330 * encounters a buffer with length()!=0
335 * Get the pointer to the start of the data.
337 const uint8_t* data() const {
342 * Get a writable pointer to the start of the data.
344 * The caller is responsible for calling unshare() first to ensure that it is
345 * actually safe to write to the buffer.
347 uint8_t* writableData() {
352 * Get the pointer to the end of the data.
354 const uint8_t* tail() const {
355 return data_ + length_;
359 * Get a writable pointer to the end of the data.
361 * The caller is responsible for calling unshare() first to ensure that it is
362 * actually safe to write to the buffer.
364 uint8_t* writableTail() {
365 return data_ + length_;
369 * Get the data length.
371 uint32_t length() const {
376 * Get the amount of head room.
378 * Returns the number of bytes in the buffer before the start of the data.
380 uint32_t headroom() const {
381 return data_ - buffer();
385 * Get the amount of tail room.
387 * Returns the number of bytes in the buffer after the end of the data.
389 uint32_t tailroom() const {
390 return bufferEnd() - tail();
394 * Get the pointer to the start of the buffer.
396 * Note that this is the pointer to the very beginning of the usable buffer,
397 * not the start of valid data within the buffer. Use the data() method to
398 * get a pointer to the start of the data within the buffer.
400 const uint8_t* buffer() const {
401 return (flags_ & kFlagExt) ? ext_.buf : int_.buf;
405 * Get a writable pointer to the start of the buffer.
407 * The caller is responsible for calling unshare() first to ensure that it is
408 * actually safe to write to the buffer.
410 uint8_t* writableBuffer() {
411 return (flags_ & kFlagExt) ? ext_.buf : int_.buf;
415 * Get the pointer to the end of the buffer.
417 * Note that this is the pointer to the very end of the usable buffer,
418 * not the end of valid data within the buffer. Use the tail() method to
419 * get a pointer to the end of the data within the buffer.
421 const uint8_t* bufferEnd() const {
422 return (flags_ & kFlagExt) ?
423 ext_.buf + ext_.capacity :
424 int_.buf + kMaxInternalDataSize;
428 * Get the total size of the buffer.
430 * This returns the total usable length of the buffer. Use the length()
431 * method to get the length of the actual valid data in this IOBuf.
433 uint32_t capacity() const {
434 return (flags_ & kFlagExt) ? ext_.capacity : kMaxInternalDataSize;
438 * Get a pointer to the next IOBuf in this chain.
443 const IOBuf* next() const {
448 * Get a pointer to the previous IOBuf in this chain.
453 const IOBuf* prev() const {
458 * Shift the data forwards in the buffer.
460 * This shifts the data pointer forwards in the buffer to increase the
461 * headroom. This is commonly used to increase the headroom in a newly
464 * The caller is responsible for ensuring that there is sufficient
465 * tailroom in the buffer before calling advance().
467 * If there is a non-zero data length, advance() will use memmove() to shift
468 * the data forwards in the buffer. In this case, the caller is responsible
469 * for making sure the buffer is unshared, so it will not affect other IOBufs
470 * that may be sharing the same underlying buffer.
472 void advance(uint32_t amount) {
473 // In debug builds, assert if there is a problem.
474 assert(amount <= tailroom());
477 memmove(data_ + amount, data_, length_);
483 * Shift the data backwards in the buffer.
485 * The caller is responsible for ensuring that there is sufficient headroom
486 * in the buffer before calling retreat().
488 * If there is a non-zero data length, retreat() will use memmove() to shift
489 * the data backwards in the buffer. In this case, the caller is responsible
490 * for making sure the buffer is unshared, so it will not affect other IOBufs
491 * that may be sharing the same underlying buffer.
493 void retreat(uint32_t amount) {
494 // In debug builds, assert if there is a problem.
495 assert(amount <= headroom());
498 memmove(data_ - amount, data_, length_);
504 * Adjust the data pointer to include more valid data at the beginning.
506 * This moves the data pointer backwards to include more of the available
507 * buffer. The caller is responsible for ensuring that there is sufficient
508 * headroom for the new data. The caller is also responsible for populating
509 * this section with valid data.
511 * This does not modify any actual data in the buffer.
513 void prepend(uint32_t amount) {
514 CHECK(amount <= headroom());
520 * Adjust the tail pointer to include more valid data at the end.
522 * This moves the tail pointer forwards to include more of the available
523 * buffer. The caller is responsible for ensuring that there is sufficient
524 * tailroom for the new data. The caller is also responsible for populating
525 * this section with valid data.
527 * This does not modify any actual data in the buffer.
529 void append(uint32_t amount) {
530 CHECK(amount <= tailroom());
535 * Adjust the data pointer forwards to include less valid data.
537 * This moves the data pointer forwards so that the first amount bytes are no
538 * longer considered valid data. The caller is responsible for ensuring that
539 * amount is less than or equal to the actual data length.
541 * This does not modify any actual data in the buffer.
543 void trimStart(uint32_t amount) {
544 CHECK(amount <= length_);
550 * Adjust the tail pointer backwards to include less valid data.
552 * This moves the tail pointer backwards so that the last amount bytes are no
553 * longer considered valid data. The caller is responsible for ensuring that
554 * amount is less than or equal to the actual data length.
556 * This does not modify any actual data in the buffer.
558 void trimEnd(uint32_t amount) {
559 CHECK(amount <= length_);
566 * Postcondition: headroom() == 0, length() == 0, tailroom() == capacity()
569 data_ = writableBuffer();
574 * Ensure that this buffer has at least minHeadroom headroom bytes and at
575 * least minTailroom tailroom bytes. The buffer must be writable
576 * (you must call unshare() before this, if necessary).
578 * Postcondition: headroom() >= minHeadroom, tailroom() >= minTailroom,
579 * the data (between data() and data() + length()) is preserved.
581 void reserve(uint32_t minHeadroom, uint32_t minTailroom) {
582 // Maybe we don't need to do anything.
583 if (headroom() >= minHeadroom && tailroom() >= minTailroom) {
586 // If the buffer is empty but we have enough total room (head + tail),
587 // move the data_ pointer around.
589 headroom() + tailroom() >= minHeadroom + minTailroom) {
590 data_ = writableBuffer() + minHeadroom;
593 // Bah, we have to do actual work.
594 reserveSlow(minHeadroom, minTailroom);
598 * Return true if this IOBuf is part of a chain of multiple IOBufs, or false
599 * if this is the only IOBuf in its chain.
601 bool isChained() const {
602 assert((next_ == this) == (prev_ == this));
603 return next_ != this;
607 * Get the number of IOBufs in this chain.
609 * Beware that this method has to walk the entire chain.
610 * Use isChained() if you just want to check if this IOBuf is part of a chain
613 uint32_t countChainElements() const;
616 * Get the length of all the data in this IOBuf chain.
618 * Beware that this method has to walk the entire chain.
620 uint64_t computeChainDataLength() const;
623 * Insert another IOBuf chain immediately before this IOBuf.
625 * For example, if there are two IOBuf chains (A, B, C) and (D, E, F),
626 * and B->prependChain(D) is called, the (D, E, F) chain will be subsumed
627 * and become part of the chain starting at A, which will now look like
630 * Note that since IOBuf chains are circular, head->prependChain(other) can
631 * be used to append the other chain at the very end of the chain pointed to
632 * by head. For example, if there are two IOBuf chains (A, B, C) and
633 * (D, E, F), and A->prependChain(D) is called, the chain starting at A will
634 * now consist of (A, B, C, D, E, F)
636 * The elements in the specified IOBuf chain will become part of this chain,
637 * and will be owned by the head of this chain. When this chain is
638 * destroyed, all elements in the supplied chain will also be destroyed.
640 * For this reason, appendChain() only accepts an rvalue-reference to a
641 * unique_ptr(), to make it clear that it is taking ownership of the supplied
642 * chain. If you have a raw pointer, you can pass in a new temporary
643 * unique_ptr around the raw pointer. If you have an existing,
644 * non-temporary unique_ptr, you must call std::move(ptr) to make it clear
645 * that you are destroying the original pointer.
647 void prependChain(std::unique_ptr<IOBuf>&& iobuf);
650 * Append another IOBuf chain immediately after this IOBuf.
652 * For example, if there are two IOBuf chains (A, B, C) and (D, E, F),
653 * and B->appendChain(D) is called, the (D, E, F) chain will be subsumed
654 * and become part of the chain starting at A, which will now look like
657 * The elements in the specified IOBuf chain will become part of this chain,
658 * and will be owned by the head of this chain. When this chain is
659 * destroyed, all elements in the supplied chain will also be destroyed.
661 * For this reason, appendChain() only accepts an rvalue-reference to a
662 * unique_ptr(), to make it clear that it is taking ownership of the supplied
663 * chain. If you have a raw pointer, you can pass in a new temporary
664 * unique_ptr around the raw pointer. If you have an existing,
665 * non-temporary unique_ptr, you must call std::move(ptr) to make it clear
666 * that you are destroying the original pointer.
668 void appendChain(std::unique_ptr<IOBuf>&& iobuf) {
669 // Just use prependChain() on the next element in our chain
670 next_->prependChain(std::move(iobuf));
674 * Remove this IOBuf from its current chain.
676 * Since ownership of all elements an IOBuf chain is normally maintained by
677 * the head of the chain, unlink() transfers ownership of this IOBuf from the
678 * chain and gives it to the caller. A new unique_ptr to the IOBuf is
679 * returned to the caller. The caller must store the returned unique_ptr (or
680 * call release() on it) to take ownership, otherwise the IOBuf will be
681 * immediately destroyed.
683 * Since unlink transfers ownership of the IOBuf to the caller, be careful
684 * not to call unlink() on the head of a chain if you already maintain
685 * ownership on the head of the chain via other means. The pop() method
686 * is a better choice for that situation.
688 std::unique_ptr<IOBuf> unlink() {
689 next_->prev_ = prev_;
690 prev_->next_ = next_;
693 return std::unique_ptr<IOBuf>(this);
697 * Remove this IOBuf from its current chain and return a unique_ptr to
698 * the IOBuf that formerly followed it in the chain.
700 std::unique_ptr<IOBuf> pop() {
702 next_->prev_ = prev_;
703 prev_->next_ = next_;
706 return std::unique_ptr<IOBuf>((next == this) ? NULL : next);
710 * Remove a subchain from this chain.
712 * Remove the subchain starting at head and ending at tail from this chain.
714 * Returns a unique_ptr pointing to head. (In other words, ownership of the
715 * head of the subchain is transferred to the caller.) If the caller ignores
716 * the return value and lets the unique_ptr be destroyed, the subchain will
717 * be immediately destroyed.
719 * The subchain referenced by the specified head and tail must be part of the
720 * same chain as the current IOBuf, but must not contain the current IOBuf.
721 * However, the specified head and tail may be equal to each other (i.e.,
722 * they may be a subchain of length 1).
724 std::unique_ptr<IOBuf> separateChain(IOBuf* head, IOBuf* tail) {
725 assert(head != this);
726 assert(tail != this);
728 head->prev_->next_ = tail->next_;
729 tail->next_->prev_ = head->prev_;
734 return std::unique_ptr<IOBuf>(head);
738 * Return true if at least one of the IOBufs in this chain are shared,
739 * or false if all of the IOBufs point to unique buffers.
741 * Use isSharedOne() to only check this IOBuf rather than the entire chain.
743 bool isShared() const {
744 const IOBuf* current = this;
746 if (current->isSharedOne()) {
749 current = current->next_;
750 if (current == this) {
757 * Return true if other IOBufs are also pointing to the buffer used by this
758 * IOBuf, and false otherwise.
760 * If this IOBuf points at a buffer owned by another (non-IOBuf) part of the
761 * code (i.e., if the IOBuf was created using wrapBuffer(), or was cloned
762 * from such an IOBuf), it is always considered shared.
764 * This only checks the current IOBuf, and not other IOBufs in the chain.
766 bool isSharedOne() const {
767 // If this is a user-owned buffer, it is always considered shared
768 if (flags_ & kFlagUserOwned) {
772 if (flags_ & kFlagExt) {
773 return ext_.sharedInfo->refcount.load(std::memory_order_acquire) > 1;
780 * Ensure that this IOBuf has a unique buffer that is not shared by other
783 * unshare() operates on an entire chain of IOBuf objects. If the chain is
784 * shared, it may also coalesce the chain when making it unique. If the
785 * chain is coalesced, subsequent IOBuf objects in the current chain will be
786 * automatically deleted.
788 * Note that buffers owned by other (non-IOBuf) users are automatically
791 * Throws std::bad_alloc on error. On error the IOBuf chain will be
794 * Currently unshare may also throw std::overflow_error if it tries to
795 * coalesce. (TODO: In the future it would be nice if unshare() were smart
796 * enough not to coalesce the entire buffer if the data is too large.
797 * However, in practice this seems unlikely to become an issue.)
808 * Ensure that this IOBuf has a unique buffer that is not shared by other
811 * unshareOne() operates on a single IOBuf object. This IOBuf will have a
812 * unique buffer after unshareOne() returns, but other IOBufs in the chain
813 * may still be shared after unshareOne() returns.
815 * Throws std::bad_alloc on error. On error the IOBuf will be unmodified.
824 * Coalesce this IOBuf chain into a single buffer.
826 * This method moves all of the data in this IOBuf chain into a single
827 * contiguous buffer, if it is not already in one buffer. After coalesce()
828 * returns, this IOBuf will be a chain of length one. Other IOBufs in the
829 * chain will be automatically deleted.
831 * After coalescing, the IOBuf will have at least as much headroom as the
832 * first IOBuf in the chain, and at least as much tailroom as the last IOBuf
835 * Throws std::bad_alloc on error. On error the IOBuf chain will be
836 * unmodified. Throws std::overflow_error if the length of the entire chain
837 * larger than can be described by a uint32_t capacity.
847 * Ensure that this chain has at least maxLength bytes available as a
848 * contiguous memory range.
850 * This method coalesces whole buffers in the chain into this buffer as
851 * necessary until this buffer's length() is at least maxLength.
853 * After coalescing, the IOBuf will have at least as much headroom as the
854 * first IOBuf in the chain, and at least as much tailroom as the last IOBuf
855 * that was coalesced.
857 * Throws std::bad_alloc on error. On error the IOBuf chain will be
858 * unmodified. Throws std::overflow_error if the length of the coalesced
859 * portion of the chain is larger than can be described by a uint32_t
860 * capacity. (Although maxLength is uint32_t, gather() doesn't split
861 * buffers, so coalescing whole buffers may result in a capacity that can't
862 * be described in uint32_t.
864 * Upon return, either enough of the chain was coalesced into a contiguous
865 * region, or the entire chain was coalesced. That is,
866 * length() >= maxLength || !isChained() is true.
868 void gather(uint32_t maxLength) {
869 if (!isChained() || length_ >= maxLength) {
872 coalesceSlow(maxLength);
876 * Return a new IOBuf chain sharing the same data as this chain.
878 * The new IOBuf chain will normally point to the same underlying data
879 * buffers as the original chain. (The one exception to this is if some of
880 * the IOBufs in this chain contain small internal data buffers which cannot
883 std::unique_ptr<IOBuf> clone() const;
886 * Return a new IOBuf with the same data as this IOBuf.
888 * The new IOBuf returned will not be part of a chain (even if this IOBuf is
889 * part of a larger chain).
891 std::unique_ptr<IOBuf> cloneOne() const;
893 // Overridden operator new and delete.
894 // These directly use malloc() and free() to allocate the space for IOBuf
895 // objects. This is needed since IOBuf::create() manually uses malloc when
896 // allocating IOBuf objects with an internal buffer.
897 void* operator new(size_t size);
898 void* operator new(size_t size, void* ptr);
899 void operator delete(void* ptr);
902 * Destructively convert this IOBuf to a fbstring efficiently.
903 * We rely on fbstring's AcquireMallocatedString constructor to
906 fbstring moveToFbString();
911 kFlagUserOwned = 0x2,
912 kFlagFreeSharedInfo = 0x4,
915 // Values for the ExternalBuf type field.
916 // We currently don't really use this for anything, other than to have it
917 // around for debugging purposes. We store it at the moment just because we
918 // have the 4 extra bytes in the ExternalBuf struct that would just be
919 // padding otherwise.
920 enum ExtBufTypeEnum {
922 kExtUserSupplied = 1,
928 SharedInfo(FreeFunction fn, void* arg);
930 // A pointer to a function to call to free the buffer when the refcount
931 // hits 0. If this is NULL, free() will be used instead.
934 std::atomic<uint32_t> refcount;
940 // SharedInfo may be NULL if kFlagUserOwned is set. It is non-NULL
941 // in all other cases.
942 SharedInfo* sharedInfo;
945 uint8_t buf[] __attribute__((aligned));
948 // The maximum size for an IOBuf object, including any internal data buffer
949 static const uint32_t kMaxIOBufSize = 256;
950 static const uint32_t kMaxInternalDataSize;
952 // Forbidden copy constructor and assignment opererator
953 IOBuf(IOBuf const &);
954 IOBuf& operator=(IOBuf const &);
957 * Create a new IOBuf with internal data.
959 * end is a pointer to the end of the IOBuf's internal data buffer.
961 explicit IOBuf(uint8_t* end);
964 * Create a new IOBuf pointing to an external buffer.
966 * The caller is responsible for holding a reference count for this new
967 * IOBuf. The IOBuf constructor does not automatically increment the
970 IOBuf(ExtBufTypeEnum type, uint32_t flags,
971 uint8_t* buf, uint32_t capacity,
972 uint8_t* data, uint32_t length,
973 SharedInfo* sharedInfo);
975 void unshareOneSlow();
976 void unshareChained();
977 void coalesceSlow(size_t maxLength=std::numeric_limits<size_t>::max());
978 // newLength must be the entire length of the buffers between this and
979 // end (no truncation)
980 void coalesceAndReallocate(
985 void decrementRefcount();
986 void reserveSlow(uint32_t minHeadroom, uint32_t minTailroom);
988 static size_t goodExtBufferSize(uint32_t minCapacity);
989 static void initExtBuffer(uint8_t* buf, size_t mallocSize,
990 SharedInfo** infoReturn,
991 uint32_t* capacityReturn);
992 static void allocExtBuffer(uint32_t minCapacity,
994 SharedInfo** infoReturn,
995 uint32_t* capacityReturn);
1002 * Links to the next and the previous IOBuf in this chain.
1004 * The chain is circularly linked (the last element in the chain points back
1005 * at the head), and next_ and prev_ can never be NULL. If this IOBuf is the
1006 * only element in the chain, next_ and prev_ will both point to this.
1012 * A pointer to the start of the data referenced by this IOBuf, and the
1013 * length of the data.
1015 * This may refer to any subsection of the actual buffer capacity.
1026 struct DeleterBase {
1027 virtual ~DeleterBase() { }
1028 virtual void dispose(void* p) = 0;
1031 template <class UniquePtr>
1032 struct UniquePtrDeleter : public DeleterBase {
1033 typedef typename UniquePtr::pointer Pointer;
1034 typedef typename UniquePtr::deleter_type Deleter;
1036 explicit UniquePtrDeleter(Deleter deleter) : deleter_(std::move(deleter)){ }
1037 void dispose(void* p) {
1039 deleter_(static_cast<Pointer>(p));
1050 static void freeUniquePtrBuffer(void* ptr, void* userData) {
1051 static_cast<DeleterBase*>(userData)->dispose(ptr);
1055 template <class UniquePtr>
1056 typename std::enable_if<detail::IsUniquePtrToSL<UniquePtr>::value,
1057 std::unique_ptr<IOBuf>>::type
1058 IOBuf::takeOwnership(UniquePtr&& buf, size_t count) {
1059 size_t size = count * sizeof(typename UniquePtr::element_type);
1060 CHECK_LT(size, size_t(std::numeric_limits<uint32_t>::max()));
1061 auto deleter = new UniquePtrDeleter<UniquePtr>(buf.get_deleter());
1062 return takeOwnership(buf.release(),
1064 &IOBuf::freeUniquePtrBuffer,
1068 inline std::unique_ptr<IOBuf> IOBuf::copyBuffer(
1069 const void* data, uint32_t size, uint32_t headroom,
1070 uint32_t minTailroom) {
1071 uint32_t capacity = headroom + size + minTailroom;
1072 std::unique_ptr<IOBuf> buf = create(capacity);
1073 buf->advance(headroom);
1074 memcpy(buf->writableData(), data, size);
1081 #endif // FOLLY_IO_IOBUF_H_