2 * Copyright 2017 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.
19 #include <glog/logging.h>
27 #include <type_traits>
29 #include <boost/iterator/iterator_facade.hpp>
31 #include <folly/FBString.h>
32 #include <folly/FBVector.h>
33 #include <folly/Portability.h>
34 #include <folly/Range.h>
35 #include <folly/portability/SysUio.h>
37 // Ignore shadowing warnings within this file, so includers can use -Wshadow.
39 FOLLY_GCC_DISABLE_WARNING("-Wshadow")
44 * An IOBuf is a pointer to a buffer of data.
46 * IOBuf objects are intended to be used primarily for networking code, and are
47 * modelled somewhat after FreeBSD's mbuf data structure, and Linux's sk_buff
50 * IOBuf objects facilitate zero-copy network programming, by allowing multiple
51 * IOBuf objects to point to the same underlying buffer of data, using a
52 * reference count to track when the buffer is no longer needed and can be
59 * The IOBuf itself is a small object containing a pointer to the buffer and
60 * information about which segment of the buffer contains valid data.
62 * The data layout looks like this:
70 * +------------+--------------------+-----------+
71 * | headroom | data | tailroom |
72 * +------------+--------------------+-----------+
74 * buffer() data() tail() bufferEnd()
76 * The length() method returns the length of the valid data; capacity()
77 * returns the entire capacity of the buffer (from buffer() to bufferEnd()).
78 * The headroom() and tailroom() methods return the amount of unused capacity
79 * available before and after the data.
85 * The buffer itself is reference counted, and multiple IOBuf objects may point
86 * to the same buffer. Each IOBuf may point to a different section of valid
87 * data within the underlying buffer. For example, if multiple protocol
88 * requests are read from the network into a single buffer, a separate IOBuf
89 * may be created for each request, all sharing the same underlying buffer.
91 * In other words, when multiple IOBufs share the same underlying buffer, the
92 * data() and tail() methods on each IOBuf may point to a different segment of
93 * the data. However, the buffer() and bufferEnd() methods will point to the
94 * same location for all IOBufs sharing the same underlying buffer.
96 * +-----------+ +---------+
97 * | IOBuf 1 | | IOBuf 2 |
98 * +-----------+ +---------+
100 * data | tail |/ data | tail
102 * +-------------------------------------+
104 * +-------------------------------------+
106 * If you only read data from an IOBuf, you don't need to worry about other
107 * IOBuf objects possibly sharing the same underlying buffer. However, if you
108 * ever write to the buffer you need to first ensure that no other IOBufs point
109 * to the same buffer. The unshare() method may be used to ensure that you
110 * have an unshared buffer.
116 * IOBuf objects also contain pointers to next and previous IOBuf objects.
117 * This can be used to represent a single logical piece of data that its stored
118 * in non-contiguous chunks in separate buffers.
120 * A single IOBuf object can only belong to one chain at a time.
122 * IOBuf chains are always circular. The "prev" pointer in the head of the
123 * chain points to the tail of the chain. However, it is up to the user to
124 * decide which IOBuf is the head. Internally the IOBuf code does not care
125 * which element is the head.
127 * The lifetime of all IOBufs in the chain are linked: when one element in the
128 * chain is deleted, all other chained elements are also deleted. Conceptually
129 * it is simplest to treat this as if the head of the chain owns all other
130 * IOBufs in the chain. When you delete the head of the chain, it will delete
131 * the other elements as well. For this reason, prependChain() and
132 * appendChain() take ownership of of the new elements being added to this
135 * When the coalesce() method is used to coalesce an entire IOBuf chain into a
136 * single IOBuf, all other IOBufs in the chain are eliminated and automatically
137 * deleted. The unshare() method may coalesce the chain; if it does it will
138 * similarly delete all IOBufs eliminated from the chain.
140 * As discussed in the following section, it is up to the user to maintain a
141 * lock around the entire IOBuf chain if multiple threads need to access the
142 * chain. IOBuf does not provide any internal locking.
148 * When used in multithread programs, a single IOBuf object should only be used
149 * in a single thread at a time. If a caller uses a single IOBuf across
150 * multiple threads the caller is responsible for using an external lock to
151 * synchronize access to the IOBuf.
153 * Two separate IOBuf objects may be accessed concurrently in separate threads
154 * without locking, even if they point to the same underlying buffer. The
155 * buffer reference count is always accessed atomically, and no other
156 * operations should affect other IOBufs that point to the same data segment.
157 * The caller is responsible for using unshare() to ensure that the data buffer
158 * is not shared by other IOBufs before writing to it, and this ensures that
159 * the data itself is not modified in one thread while also being accessed from
162 * For IOBuf chains, no two IOBufs in the same chain should be accessed
163 * simultaneously in separate threads. The caller must maintain a lock around
164 * the entire chain if the chain, or individual IOBufs in the chain, may be
165 * accessed by multiple threads.
168 * IOBuf Object Allocation
169 * -----------------------
171 * IOBuf objects themselves exist separately from the data buffer they point
172 * to. Therefore one must also consider how to allocate and manage the IOBuf
175 * It is more common to allocate IOBuf objects on the heap, using the create(),
176 * takeOwnership(), or wrapBuffer() factory functions. The clone()/cloneOne()
177 * functions also return new heap-allocated IOBufs. The createCombined()
178 * function allocates the IOBuf object and data storage space together, in a
179 * single memory allocation. This can improve performance, particularly if you
180 * know that the data buffer and the IOBuf itself will have similar lifetimes.
182 * That said, it is also possible to allocate IOBufs on the stack or inline
183 * inside another object as well. This is useful for cases where the IOBuf is
184 * short-lived, or when the overhead of allocating the IOBuf on the heap is
187 * However, note that stack-allocated IOBufs may only be used as the head of a
188 * chain (or standalone as the only IOBuf in a chain). All non-head members of
189 * an IOBuf chain must be heap allocated. (All functions to add nodes to a
190 * chain require a std::unique_ptr<IOBuf>, which enforces this requrement.)
192 * Copying IOBufs is only meaningful for the head of a chain. The entire chain
193 * is cloned; the IOBufs will become shared, and the old and new IOBufs will
194 * refer to the same underlying memory.
199 * The IOBuf class manages sharing of the underlying buffer that it points to,
200 * maintaining a reference count if multiple IOBufs are pointing at the same
203 * However, it is the callers responsibility to manage sharing and ownership of
204 * IOBuf objects themselves. The IOBuf structure does not provide room for an
205 * intrusive refcount on the IOBuf object itself, only the underlying data
206 * buffer is reference counted. If users want to share the same IOBuf object
207 * between multiple parts of the code, they are responsible for managing this
208 * sharing on their own. (For example, by using a shared_ptr. Alternatively,
209 * users always have the option of using clone() to create a second IOBuf that
210 * points to the same underlying buffer.)
213 // Is T a unique_ptr<> to a standard-layout type?
214 template <typename T>
215 struct IsUniquePtrToSL : std::false_type {};
216 template <typename T, typename D>
217 struct IsUniquePtrToSL<std::unique_ptr<T, D>> : std::is_standard_layout<T> {};
218 } // namespace detail
224 enum CreateOp { CREATE };
225 enum WrapBufferOp { WRAP_BUFFER };
226 enum TakeOwnershipOp { TAKE_OWNERSHIP };
227 enum CopyBufferOp { COPY_BUFFER };
229 typedef ByteRange value_type;
230 typedef Iterator iterator;
231 typedef Iterator const_iterator;
233 typedef void (*FreeFunction)(void* buf, void* userData);
236 * Allocate a new IOBuf object with the requested capacity.
238 * Returns a new IOBuf object that must be (eventually) deleted by the
239 * caller. The returned IOBuf may actually have slightly more capacity than
242 * The data pointer will initially point to the start of the newly allocated
243 * buffer, and will have a data length of 0.
245 * Throws std::bad_alloc on error.
247 static std::unique_ptr<IOBuf> create(uint64_t capacity);
248 IOBuf(CreateOp, uint64_t capacity);
251 * Create a new IOBuf, using a single memory allocation to allocate space
252 * for both the IOBuf object and the data storage space.
254 * This saves one memory allocation. However, it can be wasteful if you
255 * later need to grow the buffer using reserve(). If the buffer needs to be
256 * reallocated, the space originally allocated will not be freed() until the
257 * IOBuf object itself is also freed. (It can also be slightly wasteful in
258 * some cases where you clone this IOBuf and then free the original IOBuf.)
260 static std::unique_ptr<IOBuf> createCombined(uint64_t capacity);
263 * Create a new IOBuf, using separate memory allocations for the IOBuf object
264 * for the IOBuf and the data storage space.
266 * This requires two memory allocations, but saves space in the long run
267 * if you know that you will need to reallocate the data buffer later.
269 static std::unique_ptr<IOBuf> createSeparate(uint64_t capacity);
272 * Allocate a new IOBuf chain with the requested total capacity, allocating
273 * no more than maxBufCapacity to each buffer.
275 static std::unique_ptr<IOBuf> createChain(
276 size_t totalCapacity, uint64_t maxBufCapacity);
279 * Create a new IOBuf pointing to an existing data buffer.
281 * The new IOBuffer will assume ownership of the buffer, and free it by
282 * calling the specified FreeFunction when the last IOBuf pointing to this
283 * buffer is destroyed. The function will be called with a pointer to the
284 * buffer as the first argument, and the supplied userData value as the
285 * second argument. The free function must never throw exceptions.
287 * If no FreeFunction is specified, the buffer will be freed using free()
288 * which will result in undefined behavior if the memory was allocated
291 * The IOBuf data pointer will initially point to the start of the buffer,
293 * In the first version of this function, the length of data is unspecified
294 * and is initialized to the capacity of the buffer
296 * In the second version, the user specifies the valid length of data
299 * On error, std::bad_alloc will be thrown. If freeOnError is true (the
300 * default) the buffer will be freed before throwing the error.
302 static std::unique_ptr<IOBuf> takeOwnership(void* buf, uint64_t capacity,
303 FreeFunction freeFn = nullptr,
304 void* userData = nullptr,
305 bool freeOnError = true) {
306 return takeOwnership(buf, capacity, capacity, freeFn,
307 userData, freeOnError);
309 IOBuf(TakeOwnershipOp op, void* buf, uint64_t capacity,
310 FreeFunction freeFn = nullptr, void* userData = nullptr,
311 bool freeOnError = true)
312 : IOBuf(op, buf, capacity, capacity, freeFn, userData, freeOnError) {}
314 static std::unique_ptr<IOBuf> takeOwnership(void* buf, uint64_t capacity,
316 FreeFunction freeFn = nullptr,
317 void* userData = nullptr,
318 bool freeOnError = true);
319 IOBuf(TakeOwnershipOp, void* buf, uint64_t capacity, uint64_t length,
320 FreeFunction freeFn = nullptr, void* userData = nullptr,
321 bool freeOnError = true);
324 * Create a new IOBuf pointing to an existing data buffer made up of
325 * count objects of a given standard-layout type.
327 * This is dangerous -- it is essentially equivalent to doing
328 * reinterpret_cast<unsigned char*> on your data -- but it's often useful
329 * for serialization / deserialization.
331 * The new IOBuffer will assume ownership of the buffer, and free it
332 * appropriately (by calling the UniquePtr's custom deleter, or by calling
333 * delete or delete[] appropriately if there is no custom deleter)
334 * when the buffer is destroyed. The custom deleter, if any, must never
337 * The IOBuf data pointer will initially point to the start of the buffer,
338 * and the length will be the full capacity of the buffer (count *
341 * On error, std::bad_alloc will be thrown, and the buffer will be freed
342 * before throwing the error.
344 template <class UniquePtr>
345 static typename std::enable_if<detail::IsUniquePtrToSL<UniquePtr>::value,
346 std::unique_ptr<IOBuf>>::type
347 takeOwnership(UniquePtr&& buf, size_t count=1);
350 * Create a new IOBuf object that points to an existing user-owned buffer.
352 * This should only be used when the caller knows the lifetime of the IOBuf
353 * object ahead of time and can ensure that all IOBuf objects that will point
354 * to this buffer will be destroyed before the buffer itself is destroyed.
356 * This buffer will not be freed automatically when the last IOBuf
357 * referencing it is destroyed. It is the caller's responsibility to free
358 * the buffer after the last IOBuf has been destroyed.
360 * The IOBuf data pointer will initially point to the start of the buffer,
361 * and the length will be the full capacity of the buffer.
363 * An IOBuf created using wrapBuffer() will always be reported as shared.
364 * unshare() may be used to create a writable copy of the buffer.
366 * On error, std::bad_alloc will be thrown.
368 static std::unique_ptr<IOBuf> wrapBuffer(const void* buf, uint64_t capacity);
369 static std::unique_ptr<IOBuf> wrapBuffer(ByteRange br) {
370 return wrapBuffer(br.data(), br.size());
374 * Similar to wrapBuffer(), but returns IOBuf by value rather than
375 * heap-allocating it.
377 static IOBuf wrapBufferAsValue(const void* buf, uint64_t capacity);
378 static IOBuf wrapBufferAsValue(ByteRange br) {
379 return wrapBufferAsValue(br.data(), br.size());
382 IOBuf(WrapBufferOp op, const void* buf, uint64_t capacity);
383 IOBuf(WrapBufferOp op, ByteRange br);
386 * Convenience function to create a new IOBuf object that copies data from a
387 * user-supplied buffer, optionally allocating a given amount of
388 * headroom and tailroom.
390 static std::unique_ptr<IOBuf> copyBuffer(const void* buf, uint64_t size,
392 uint64_t minTailroom=0);
393 static std::unique_ptr<IOBuf> copyBuffer(ByteRange br,
395 uint64_t minTailroom=0) {
396 return copyBuffer(br.data(), br.size(), headroom, minTailroom);
398 IOBuf(CopyBufferOp op, const void* buf, uint64_t size,
399 uint64_t headroom=0, uint64_t minTailroom=0);
400 IOBuf(CopyBufferOp op, ByteRange br,
401 uint64_t headroom=0, uint64_t minTailroom=0);
404 * Convenience function to create a new IOBuf object that copies data from a
405 * user-supplied string, optionally allocating a given amount of
406 * headroom and tailroom.
408 * Beware when attempting to invoke this function with a constant string
409 * literal and a headroom argument: you will likely end up invoking the
410 * version of copyBuffer() above. IOBuf::copyBuffer("hello", 3) will treat
411 * the first argument as a const void*, and will invoke the version of
412 * copyBuffer() above, with the size argument of 3.
414 static std::unique_ptr<IOBuf> copyBuffer(const std::string& buf,
416 uint64_t minTailroom=0);
417 IOBuf(CopyBufferOp op, const std::string& buf,
418 uint64_t headroom=0, uint64_t minTailroom=0)
419 : IOBuf(op, buf.data(), buf.size(), headroom, minTailroom) {}
422 * A version of copyBuffer() that returns a null pointer if the input string
425 static std::unique_ptr<IOBuf> maybeCopyBuffer(const std::string& buf,
427 uint64_t minTailroom=0);
430 * Convenience function to free a chain of IOBufs held by a unique_ptr.
432 static void destroy(std::unique_ptr<IOBuf>&& data) {
433 auto destroyer = std::move(data);
437 * Destroy this IOBuf.
439 * Deleting an IOBuf will automatically destroy all IOBufs in the chain.
440 * (See the comments above regarding the ownership model of IOBuf chains.
441 * All subsequent IOBufs in the chain are considered to be owned by the head
442 * of the chain. Users should only explicitly delete the head of a chain.)
444 * When each individual IOBuf is destroyed, it will release its reference
445 * count on the underlying buffer. If it was the last user of the buffer,
446 * the buffer will be freed.
451 * Check whether the chain is empty (i.e., whether the IOBufs in the
452 * chain have a total data length of zero).
454 * This method is semantically equivalent to
455 * i->computeChainDataLength()==0
456 * but may run faster because it can short-circuit as soon as it
457 * encounters a buffer with length()!=0
462 * Get the pointer to the start of the data.
464 const uint8_t* data() const {
469 * Get a writable pointer to the start of the data.
471 * The caller is responsible for calling unshare() first to ensure that it is
472 * actually safe to write to the buffer.
474 uint8_t* writableData() {
479 * Get the pointer to the end of the data.
481 const uint8_t* tail() const {
482 return data_ + length_;
486 * Get a writable pointer to the end of the data.
488 * The caller is responsible for calling unshare() first to ensure that it is
489 * actually safe to write to the buffer.
491 uint8_t* writableTail() {
492 return data_ + length_;
496 * Get the data length.
498 uint64_t length() const {
503 * Get the amount of head room.
505 * Returns the number of bytes in the buffer before the start of the data.
507 uint64_t headroom() const {
508 return uint64_t(data_ - buffer());
512 * Get the amount of tail room.
514 * Returns the number of bytes in the buffer after the end of the data.
516 uint64_t tailroom() const {
517 return uint64_t(bufferEnd() - tail());
521 * Get the pointer to the start of the buffer.
523 * Note that this is the pointer to the very beginning of the usable buffer,
524 * not the start of valid data within the buffer. Use the data() method to
525 * get a pointer to the start of the data within the buffer.
527 const uint8_t* buffer() const {
532 * Get a writable pointer to the start of the buffer.
534 * The caller is responsible for calling unshare() first to ensure that it is
535 * actually safe to write to the buffer.
537 uint8_t* writableBuffer() {
542 * Get the pointer to the end of the buffer.
544 * Note that this is the pointer to the very end of the usable buffer,
545 * not the end of valid data within the buffer. Use the tail() method to
546 * get a pointer to the end of the data within the buffer.
548 const uint8_t* bufferEnd() const {
549 return buf_ + capacity_;
553 * Get the total size of the buffer.
555 * This returns the total usable length of the buffer. Use the length()
556 * method to get the length of the actual valid data in this IOBuf.
558 uint64_t capacity() const {
563 * Get a pointer to the next IOBuf in this chain.
568 const IOBuf* next() const {
573 * Get a pointer to the previous IOBuf in this chain.
578 const IOBuf* prev() const {
583 * Shift the data forwards in the buffer.
585 * This shifts the data pointer forwards in the buffer to increase the
586 * headroom. This is commonly used to increase the headroom in a newly
589 * The caller is responsible for ensuring that there is sufficient
590 * tailroom in the buffer before calling advance().
592 * If there is a non-zero data length, advance() will use memmove() to shift
593 * the data forwards in the buffer. In this case, the caller is responsible
594 * for making sure the buffer is unshared, so it will not affect other IOBufs
595 * that may be sharing the same underlying buffer.
597 void advance(uint64_t amount) {
598 // In debug builds, assert if there is a problem.
599 assert(amount <= tailroom());
602 memmove(data_ + amount, data_, length_);
608 * Shift the data backwards in the buffer.
610 * The caller is responsible for ensuring that there is sufficient headroom
611 * in the buffer before calling retreat().
613 * If there is a non-zero data length, retreat() will use memmove() to shift
614 * the data backwards in the buffer. In this case, the caller is responsible
615 * for making sure the buffer is unshared, so it will not affect other IOBufs
616 * that may be sharing the same underlying buffer.
618 void retreat(uint64_t amount) {
619 // In debug builds, assert if there is a problem.
620 assert(amount <= headroom());
623 memmove(data_ - amount, data_, length_);
629 * Adjust the data pointer to include more valid data at the beginning.
631 * This moves the data pointer backwards to include more of the available
632 * buffer. The caller is responsible for ensuring that there is sufficient
633 * headroom for the new data. The caller is also responsible for populating
634 * this section with valid data.
636 * This does not modify any actual data in the buffer.
638 void prepend(uint64_t amount) {
639 DCHECK_LE(amount, headroom());
645 * Adjust the tail pointer to include more valid data at the end.
647 * This moves the tail pointer forwards to include more of the available
648 * buffer. The caller is responsible for ensuring that there is sufficient
649 * tailroom for the new data. The caller is also responsible for populating
650 * this section with valid data.
652 * This does not modify any actual data in the buffer.
654 void append(uint64_t amount) {
655 DCHECK_LE(amount, tailroom());
660 * Adjust the data pointer forwards to include less valid data.
662 * This moves the data pointer forwards so that the first amount bytes are no
663 * longer considered valid data. The caller is responsible for ensuring that
664 * amount is less than or equal to the actual data length.
666 * This does not modify any actual data in the buffer.
668 void trimStart(uint64_t amount) {
669 DCHECK_LE(amount, length_);
675 * Adjust the tail pointer backwards to include less valid data.
677 * This moves the tail pointer backwards so that the last amount bytes are no
678 * longer considered valid data. The caller is responsible for ensuring that
679 * amount is less than or equal to the actual data length.
681 * This does not modify any actual data in the buffer.
683 void trimEnd(uint64_t amount) {
684 DCHECK_LE(amount, length_);
691 * Postcondition: headroom() == 0, length() == 0, tailroom() == capacity()
694 data_ = writableBuffer();
699 * Ensure that this buffer has at least minHeadroom headroom bytes and at
700 * least minTailroom tailroom bytes. The buffer must be writable
701 * (you must call unshare() before this, if necessary).
703 * Postcondition: headroom() >= minHeadroom, tailroom() >= minTailroom,
704 * the data (between data() and data() + length()) is preserved.
706 void reserve(uint64_t minHeadroom, uint64_t minTailroom) {
707 // Maybe we don't need to do anything.
708 if (headroom() >= minHeadroom && tailroom() >= minTailroom) {
711 // If the buffer is empty but we have enough total room (head + tail),
712 // move the data_ pointer around.
714 headroom() + tailroom() >= minHeadroom + minTailroom) {
715 data_ = writableBuffer() + minHeadroom;
718 // Bah, we have to do actual work.
719 reserveSlow(minHeadroom, minTailroom);
723 * Return true if this IOBuf is part of a chain of multiple IOBufs, or false
724 * if this is the only IOBuf in its chain.
726 bool isChained() const {
727 assert((next_ == this) == (prev_ == this));
728 return next_ != this;
732 * Get the number of IOBufs in this chain.
734 * Beware that this method has to walk the entire chain.
735 * Use isChained() if you just want to check if this IOBuf is part of a chain
738 size_t countChainElements() const;
741 * Get the length of all the data in this IOBuf chain.
743 * Beware that this method has to walk the entire chain.
745 uint64_t computeChainDataLength() const;
748 * Insert another IOBuf chain immediately before this IOBuf.
750 * For example, if there are two IOBuf chains (A, B, C) and (D, E, F),
751 * and B->prependChain(D) is called, the (D, E, F) chain will be subsumed
752 * and become part of the chain starting at A, which will now look like
755 * Note that since IOBuf chains are circular, head->prependChain(other) can
756 * be used to append the other chain at the very end of the chain pointed to
757 * by head. For example, if there are two IOBuf chains (A, B, C) and
758 * (D, E, F), and A->prependChain(D) is called, the chain starting at A will
759 * now consist of (A, B, C, D, E, F)
761 * The elements in the specified IOBuf chain will become part of this chain,
762 * and will be owned by the head of this chain. When this chain is
763 * destroyed, all elements in the supplied chain will also be destroyed.
765 * For this reason, appendChain() only accepts an rvalue-reference to a
766 * unique_ptr(), to make it clear that it is taking ownership of the supplied
767 * chain. If you have a raw pointer, you can pass in a new temporary
768 * unique_ptr around the raw pointer. If you have an existing,
769 * non-temporary unique_ptr, you must call std::move(ptr) to make it clear
770 * that you are destroying the original pointer.
772 void prependChain(std::unique_ptr<IOBuf>&& iobuf);
775 * Append another IOBuf chain immediately after this IOBuf.
777 * For example, if there are two IOBuf chains (A, B, C) and (D, E, F),
778 * and B->appendChain(D) is called, the (D, E, F) chain will be subsumed
779 * and become part of the chain starting at A, which will now look like
782 * The elements in the specified IOBuf chain will become part of this chain,
783 * and will be owned by the head of this chain. When this chain is
784 * destroyed, all elements in the supplied chain will also be destroyed.
786 * For this reason, appendChain() only accepts an rvalue-reference to a
787 * unique_ptr(), to make it clear that it is taking ownership of the supplied
788 * chain. If you have a raw pointer, you can pass in a new temporary
789 * unique_ptr around the raw pointer. If you have an existing,
790 * non-temporary unique_ptr, you must call std::move(ptr) to make it clear
791 * that you are destroying the original pointer.
793 void appendChain(std::unique_ptr<IOBuf>&& iobuf) {
794 // Just use prependChain() on the next element in our chain
795 next_->prependChain(std::move(iobuf));
799 * Remove this IOBuf from its current chain.
801 * Since ownership of all elements an IOBuf chain is normally maintained by
802 * the head of the chain, unlink() transfers ownership of this IOBuf from the
803 * chain and gives it to the caller. A new unique_ptr to the IOBuf is
804 * returned to the caller. The caller must store the returned unique_ptr (or
805 * call release() on it) to take ownership, otherwise the IOBuf will be
806 * immediately destroyed.
808 * Since unlink transfers ownership of the IOBuf to the caller, be careful
809 * not to call unlink() on the head of a chain if you already maintain
810 * ownership on the head of the chain via other means. The pop() method
811 * is a better choice for that situation.
813 std::unique_ptr<IOBuf> unlink() {
814 next_->prev_ = prev_;
815 prev_->next_ = next_;
818 return std::unique_ptr<IOBuf>(this);
822 * Remove this IOBuf from its current chain and return a unique_ptr to
823 * the IOBuf that formerly followed it in the chain.
825 std::unique_ptr<IOBuf> pop() {
827 next_->prev_ = prev_;
828 prev_->next_ = next_;
831 return std::unique_ptr<IOBuf>((next == this) ? nullptr : next);
835 * Remove a subchain from this chain.
837 * Remove the subchain starting at head and ending at tail from this chain.
839 * Returns a unique_ptr pointing to head. (In other words, ownership of the
840 * head of the subchain is transferred to the caller.) If the caller ignores
841 * the return value and lets the unique_ptr be destroyed, the subchain will
842 * be immediately destroyed.
844 * The subchain referenced by the specified head and tail must be part of the
845 * same chain as the current IOBuf, but must not contain the current IOBuf.
846 * However, the specified head and tail may be equal to each other (i.e.,
847 * they may be a subchain of length 1).
849 std::unique_ptr<IOBuf> separateChain(IOBuf* head, IOBuf* tail) {
850 assert(head != this);
851 assert(tail != this);
853 head->prev_->next_ = tail->next_;
854 tail->next_->prev_ = head->prev_;
859 return std::unique_ptr<IOBuf>(head);
863 * Return true if at least one of the IOBufs in this chain are shared,
864 * or false if all of the IOBufs point to unique buffers.
866 * Use isSharedOne() to only check this IOBuf rather than the entire chain.
868 bool isShared() const {
869 const IOBuf* current = this;
871 if (current->isSharedOne()) {
874 current = current->next_;
875 if (current == this) {
882 * Return true if all IOBufs in this chain are managed by the usual
883 * refcounting mechanism (and so the lifetime of the underlying memory
884 * can be extended by clone()).
886 bool isManaged() const {
887 const IOBuf* current = this;
889 if (!current->isManagedOne()) {
892 current = current->next_;
893 if (current == this) {
900 * Return true if this IOBuf is managed by the usual refcounting mechanism
901 * (and so the lifetime of the underlying memory can be extended by
904 bool isManagedOne() const {
909 * Return true if other IOBufs are also pointing to the buffer used by this
910 * IOBuf, and false otherwise.
912 * If this IOBuf points at a buffer owned by another (non-IOBuf) part of the
913 * code (i.e., if the IOBuf was created using wrapBuffer(), or was cloned
914 * from such an IOBuf), it is always considered shared.
916 * This only checks the current IOBuf, and not other IOBufs in the chain.
918 bool isSharedOne() const {
919 // If this is a user-owned buffer, it is always considered shared
920 if (UNLIKELY(!sharedInfo())) {
924 if (UNLIKELY(sharedInfo()->externallyShared)) {
928 if (LIKELY(!(flags() & kFlagMaybeShared))) {
932 // kFlagMaybeShared is set, so we need to check the reference count.
933 // (Checking the reference count requires an atomic operation, which is why
934 // we prefer to only check kFlagMaybeShared if possible.)
935 bool shared = sharedInfo()->refcount.load(std::memory_order_acquire) > 1;
937 // we're the last one left
938 clearFlags(kFlagMaybeShared);
944 * Ensure that this IOBuf has a unique buffer that is not shared by other
947 * unshare() operates on an entire chain of IOBuf objects. If the chain is
948 * shared, it may also coalesce the chain when making it unique. If the
949 * chain is coalesced, subsequent IOBuf objects in the current chain will be
950 * automatically deleted.
952 * Note that buffers owned by other (non-IOBuf) users are automatically
955 * Throws std::bad_alloc on error. On error the IOBuf chain will be
958 * Currently unshare may also throw std::overflow_error if it tries to
959 * coalesce. (TODO: In the future it would be nice if unshare() were smart
960 * enough not to coalesce the entire buffer if the data is too large.
961 * However, in practice this seems unlikely to become an issue.)
972 * Ensure that this IOBuf has a unique buffer that is not shared by other
975 * unshareOne() operates on a single IOBuf object. This IOBuf will have a
976 * unique buffer after unshareOne() returns, but other IOBufs in the chain
977 * may still be shared after unshareOne() returns.
979 * Throws std::bad_alloc on error. On error the IOBuf will be unmodified.
988 * Mark the underlying buffers in this chain as shared with external memory
989 * management mechanism. This will make isShared() always returns true.
991 * This function is not thread-safe, and only safe to call immediately after
992 * creating an IOBuf, before it has been shared with other threads.
994 void markExternallyShared();
997 * Mark the underlying buffer that this IOBuf refers to as shared with
998 * external memory management mechanism. This will make isSharedOne() always
1001 * This function is not thread-safe, and only safe to call immediately after
1002 * creating an IOBuf, before it has been shared with other threads.
1004 void markExternallySharedOne() {
1005 SharedInfo* info = sharedInfo();
1007 info->externallyShared = true;
1012 * Ensure that the memory that IOBufs in this chain refer to will continue to
1013 * be allocated for as long as the IOBufs of the chain (or any clone()s
1014 * created from this point onwards) is alive.
1016 * This only has an effect for user-owned buffers (created with the
1017 * WRAP_BUFFER constructor or wrapBuffer factory function), in which case
1018 * those buffers are unshared.
1020 void makeManaged() {
1022 makeManagedChained();
1029 * Ensure that the memory that this IOBuf refers to will continue to be
1030 * allocated for as long as this IOBuf (or any clone()s created from this
1031 * point onwards) is alive.
1033 * This only has an effect for user-owned buffers (created with the
1034 * WRAP_BUFFER constructor or wrapBuffer factory function), in which case
1035 * those buffers are unshared.
1037 void makeManagedOne() {
1038 if (!isManagedOne()) {
1039 // We can call the internal function directly; unmanaged implies shared.
1045 * Coalesce this IOBuf chain into a single buffer.
1047 * This method moves all of the data in this IOBuf chain into a single
1048 * contiguous buffer, if it is not already in one buffer. After coalesce()
1049 * returns, this IOBuf will be a chain of length one. Other IOBufs in the
1050 * chain will be automatically deleted.
1052 * After coalescing, the IOBuf will have at least as much headroom as the
1053 * first IOBuf in the chain, and at least as much tailroom as the last IOBuf
1056 * Throws std::bad_alloc on error. On error the IOBuf chain will be
1059 * Returns ByteRange that points to the data IOBuf stores.
1061 ByteRange coalesce() {
1065 return ByteRange(data_, length_);
1069 * Ensure that this chain has at least maxLength bytes available as a
1070 * contiguous memory range.
1072 * This method coalesces whole buffers in the chain into this buffer as
1073 * necessary until this buffer's length() is at least maxLength.
1075 * After coalescing, the IOBuf will have at least as much headroom as the
1076 * first IOBuf in the chain, and at least as much tailroom as the last IOBuf
1077 * that was coalesced.
1079 * Throws std::bad_alloc or std::overflow_error on error. On error the IOBuf
1080 * chain will be unmodified. Throws std::overflow_error if maxLength is
1081 * longer than the total chain length.
1083 * Upon return, either enough of the chain was coalesced into a contiguous
1084 * region, or the entire chain was coalesced. That is,
1085 * length() >= maxLength || !isChained() is true.
1087 void gather(uint64_t maxLength) {
1088 if (!isChained() || length_ >= maxLength) {
1091 coalesceSlow(maxLength);
1095 * Return a new IOBuf chain sharing the same data as this chain.
1097 * The new IOBuf chain will normally point to the same underlying data
1098 * buffers as the original chain. (The one exception to this is if some of
1099 * the IOBufs in this chain contain small internal data buffers which cannot
1102 std::unique_ptr<IOBuf> clone() const;
1105 * Similar to clone(). But returns IOBuf by value rather than heap-allocating
1108 IOBuf cloneAsValue() const;
1111 * Return a new IOBuf with the same data as this IOBuf.
1113 * The new IOBuf returned will not be part of a chain (even if this IOBuf is
1114 * part of a larger chain).
1116 std::unique_ptr<IOBuf> cloneOne() const;
1119 * Similar to cloneOne(). But returns IOBuf by value rather than
1120 * heap-allocating it.
1122 IOBuf cloneOneAsValue() const;
1125 * Return a new unchained IOBuf that may share the same data as this chain.
1127 * If the IOBuf chain is not chained then the new IOBuf will point to the same
1128 * underlying data buffer as the original chain. Otherwise, it will clone and
1129 * coalesce the IOBuf chain.
1131 * The new IOBuf will have at least as much headroom as the first IOBuf in the
1132 * chain, and at least as much tailroom as the last IOBuf in the chain.
1134 * Throws std::bad_alloc on error.
1136 std::unique_ptr<IOBuf> cloneCoalesced() const;
1139 * Similar to cloneCoalesced(). But returns IOBuf by value rather than
1140 * heap-allocating it.
1142 IOBuf cloneCoalescedAsValue() const;
1145 * Similar to Clone(). But use other as the head node. Other nodes in the
1146 * chain (if any) will be allocted on heap.
1148 void cloneInto(IOBuf& other) const {
1149 other = cloneAsValue();
1153 * Similar to CloneOne(). But to fill an existing IOBuf instead of a new
1156 void cloneOneInto(IOBuf& other) const {
1157 other = cloneOneAsValue();
1161 * Return an iovector suitable for e.g. writev()
1163 * auto iov = buf->getIov();
1164 * auto xfer = writev(fd, iov.data(), iov.size());
1166 * Naturally, the returned iovector is invalid if you modify the buffer
1169 folly::fbvector<struct iovec> getIov() const;
1172 * Update an existing iovec array with the IOBuf data.
1174 * New iovecs will be appended to the existing vector; anything already
1175 * present in the vector will be left unchanged.
1177 * Naturally, the returned iovec data will be invalid if you modify the
1180 void appendToIov(folly::fbvector<struct iovec>* iov) const;
1183 * Fill an iovec array with the IOBuf data.
1185 * Returns the number of iovec filled. If there are more buffer than
1186 * iovec, returns 0. This version is suitable to use with stack iovec
1189 * Naturally, the filled iovec data will be invalid if you modify the
1192 size_t fillIov(struct iovec* iov, size_t len) const;
1195 * Overridden operator new and delete.
1196 * These perform specialized memory management to help support
1197 * createCombined(), which allocates IOBuf objects together with the buffer
1200 void* operator new(size_t size);
1201 void* operator new(size_t size, void* ptr);
1202 void operator delete(void* ptr);
1205 * Destructively convert this IOBuf to a fbstring efficiently.
1206 * We rely on fbstring's AcquireMallocatedString constructor to
1209 fbstring moveToFbString();
1212 * Iteration support: a chain of IOBufs may be iterated through using
1213 * STL-style iterators over const ByteRanges. Iterators are only invalidated
1214 * if the IOBuf that they currently point to is removed.
1216 Iterator cbegin() const;
1217 Iterator cend() const;
1218 Iterator begin() const;
1219 Iterator end() const;
1222 * Allocate a new null buffer.
1224 * This can be used to allocate an empty IOBuf on the stack. It will have no
1225 * space allocated for it. This is generally useful only to later use move
1226 * assignment to fill out the IOBuf.
1231 * Move constructor and assignment operator.
1233 * In general, you should only ever move the head of an IOBuf chain.
1234 * Internal nodes in an IOBuf chain are owned by the head of the chain, and
1235 * should not be moved from. (Technically, nothing prevents you from moving
1236 * a non-head node, but the moved-to node will replace the moved-from node in
1237 * the chain. This has implications for ownership, since non-head nodes are
1238 * owned by the chain head. You are then responsible for relinquishing
1239 * ownership of the moved-to node, and manually deleting the moved-from
1242 * With the move assignment operator, the destination of the move should be
1243 * the head of an IOBuf chain or a solitary IOBuf not part of a chain. If
1244 * the move destination is part of a chain, all other IOBufs in the chain
1247 IOBuf(IOBuf&& other) noexcept;
1248 IOBuf& operator=(IOBuf&& other) noexcept;
1250 IOBuf(const IOBuf& other);
1251 IOBuf& operator=(const IOBuf& other);
1254 enum FlagsEnum : uintptr_t {
1255 // Adding any more flags would not work on 32-bit architectures,
1256 // as these flags are stashed in the least significant 2 bits of a
1257 // max-align-aligned pointer.
1258 kFlagFreeSharedInfo = 0x1,
1259 kFlagMaybeShared = 0x2,
1260 kFlagMask = kFlagFreeSharedInfo | kFlagMaybeShared
1265 SharedInfo(FreeFunction fn, void* arg);
1267 // A pointer to a function to call to free the buffer when the refcount
1268 // hits 0. If this is null, free() will be used instead.
1269 FreeFunction freeFn;
1271 std::atomic<uint32_t> refcount;
1272 bool externallyShared{false};
1274 // Helper structs for use by operator new and delete
1277 struct HeapFullStorage;
1280 * Create a new IOBuf pointing to an external buffer.
1282 * The caller is responsible for holding a reference count for this new
1283 * IOBuf. The IOBuf constructor does not automatically increment the
1286 struct InternalConstructor {}; // avoid conflicts
1287 IOBuf(InternalConstructor, uintptr_t flagsAndSharedInfo,
1288 uint8_t* buf, uint64_t capacity,
1289 uint8_t* data, uint64_t length);
1291 void unshareOneSlow();
1292 void unshareChained();
1293 void makeManagedChained();
1294 void coalesceSlow();
1295 void coalesceSlow(size_t maxLength);
1296 // newLength must be the entire length of the buffers between this and
1297 // end (no truncation)
1298 void coalesceAndReallocate(
1302 size_t newTailroom);
1303 void coalesceAndReallocate(size_t newLength, IOBuf* end) {
1304 coalesceAndReallocate(headroom(), newLength, end, end->prev_->tailroom());
1306 void decrementRefcount();
1307 void reserveSlow(uint64_t minHeadroom, uint64_t minTailroom);
1308 void freeExtBuffer();
1310 static size_t goodExtBufferSize(uint64_t minCapacity);
1311 static void initExtBuffer(uint8_t* buf, size_t mallocSize,
1312 SharedInfo** infoReturn,
1313 uint64_t* capacityReturn);
1314 static void allocExtBuffer(uint64_t minCapacity,
1315 uint8_t** bufReturn,
1316 SharedInfo** infoReturn,
1317 uint64_t* capacityReturn);
1318 static void releaseStorage(HeapStorage* storage, uint16_t freeFlags);
1319 static void freeInternalBuf(void* buf, void* userData);
1326 * Links to the next and the previous IOBuf in this chain.
1328 * The chain is circularly linked (the last element in the chain points back
1329 * at the head), and next_ and prev_ can never be null. If this IOBuf is the
1330 * only element in the chain, next_ and prev_ will both point to this.
1336 * A pointer to the start of the data referenced by this IOBuf, and the
1337 * length of the data.
1339 * This may refer to any subsection of the actual buffer capacity.
1341 uint8_t* data_{nullptr};
1342 uint8_t* buf_{nullptr};
1343 uint64_t length_{0};
1344 uint64_t capacity_{0};
1346 // Pack flags in least significant 2 bits, sharedInfo in the rest
1347 mutable uintptr_t flagsAndSharedInfo_{0};
1349 static inline uintptr_t packFlagsAndSharedInfo(uintptr_t flags,
1351 uintptr_t uinfo = reinterpret_cast<uintptr_t>(info);
1352 DCHECK_EQ(flags & ~kFlagMask, 0u);
1353 DCHECK_EQ(uinfo & kFlagMask, 0u);
1354 return flags | uinfo;
1357 inline SharedInfo* sharedInfo() const {
1358 return reinterpret_cast<SharedInfo*>(flagsAndSharedInfo_ & ~kFlagMask);
1361 inline void setSharedInfo(SharedInfo* info) {
1362 uintptr_t uinfo = reinterpret_cast<uintptr_t>(info);
1363 DCHECK_EQ(uinfo & kFlagMask, 0u);
1364 flagsAndSharedInfo_ = (flagsAndSharedInfo_ & kFlagMask) | uinfo;
1367 inline uintptr_t flags() const {
1368 return flagsAndSharedInfo_ & kFlagMask;
1371 // flags_ are changed from const methods
1372 inline void setFlags(uintptr_t flags) const {
1373 DCHECK_EQ(flags & ~kFlagMask, 0u);
1374 flagsAndSharedInfo_ |= flags;
1377 inline void clearFlags(uintptr_t flags) const {
1378 DCHECK_EQ(flags & ~kFlagMask, 0u);
1379 flagsAndSharedInfo_ &= ~flags;
1382 inline void setFlagsAndSharedInfo(uintptr_t flags, SharedInfo* info) {
1383 flagsAndSharedInfo_ = packFlagsAndSharedInfo(flags, info);
1386 struct DeleterBase {
1387 virtual ~DeleterBase() { }
1388 virtual void dispose(void* p) = 0;
1391 template <class UniquePtr>
1392 struct UniquePtrDeleter : public DeleterBase {
1393 typedef typename UniquePtr::pointer Pointer;
1394 typedef typename UniquePtr::deleter_type Deleter;
1396 explicit UniquePtrDeleter(Deleter deleter) : deleter_(std::move(deleter)){ }
1397 void dispose(void* p) override {
1399 deleter_(static_cast<Pointer>(p));
1410 static void freeUniquePtrBuffer(void* ptr, void* userData) {
1411 static_cast<DeleterBase*>(userData)->dispose(ptr);
1416 * Hasher for IOBuf objects. Hashes the entire chain using SpookyHashV2.
1419 size_t operator()(const IOBuf& buf) const;
1420 size_t operator()(const std::unique_ptr<IOBuf>& buf) const {
1421 return buf ? (*this)(*buf) : 0;
1426 * Equality predicate for IOBuf objects. Compares data in the entire chain.
1429 bool operator()(const IOBuf& a, const IOBuf& b) const;
1430 bool operator()(const std::unique_ptr<IOBuf>& a,
1431 const std::unique_ptr<IOBuf>& b) const {
1434 } else if (!a || !b) {
1437 return (*this)(*a, *b);
1442 template <class UniquePtr>
1443 typename std::enable_if<detail::IsUniquePtrToSL<UniquePtr>::value,
1444 std::unique_ptr<IOBuf>>::type
1445 IOBuf::takeOwnership(UniquePtr&& buf, size_t count) {
1446 size_t size = count * sizeof(typename UniquePtr::element_type);
1447 auto deleter = new UniquePtrDeleter<UniquePtr>(buf.get_deleter());
1448 return takeOwnership(buf.release(),
1450 &IOBuf::freeUniquePtrBuffer,
1454 inline std::unique_ptr<IOBuf> IOBuf::copyBuffer(
1455 const void* data, uint64_t size, uint64_t headroom,
1456 uint64_t minTailroom) {
1457 uint64_t capacity = headroom + size + minTailroom;
1458 std::unique_ptr<IOBuf> buf = create(capacity);
1459 buf->advance(headroom);
1461 memcpy(buf->writableData(), data, size);
1467 inline std::unique_ptr<IOBuf> IOBuf::copyBuffer(const std::string& buf,
1469 uint64_t minTailroom) {
1470 return copyBuffer(buf.data(), buf.size(), headroom, minTailroom);
1473 inline std::unique_ptr<IOBuf> IOBuf::maybeCopyBuffer(const std::string& buf,
1475 uint64_t minTailroom) {
1479 return copyBuffer(buf.data(), buf.size(), headroom, minTailroom);
1482 class IOBuf::Iterator : public boost::iterator_facade<
1483 IOBuf::Iterator, // Derived
1484 const ByteRange, // Value
1485 boost::forward_traversal_tag // Category or traversal
1487 friend class boost::iterator_core_access;
1489 // Note that IOBufs are stored as a circular list without a guard node,
1490 // so pos == end is ambiguous (it may mean "begin" or "end"). To solve
1491 // the ambiguity (at the cost of one extra comparison in the "increment"
1492 // code path), we define end iterators as having pos_ == end_ == nullptr
1493 // and we only allow forward iteration.
1494 explicit Iterator(const IOBuf* pos, const IOBuf* end)
1497 // Sadly, we must return by const reference, not by value.
1507 val_ = ByteRange(pos_->data(), pos_->tail());
1510 void adjustForEnd() {
1512 pos_ = end_ = nullptr;
1519 const ByteRange& dereference() const {
1523 bool equal(const Iterator& other) const {
1524 // We must compare end_ in addition to pos_, because forward traversal
1525 // requires that if two iterators are equal (a == b) and dereferenceable,
1527 return pos_ == other.pos_ && end_ == other.end_;
1531 pos_ = pos_->next();
1535 const IOBuf* pos_{nullptr};
1536 const IOBuf* end_{nullptr};
1540 inline IOBuf::Iterator IOBuf::begin() const { return cbegin(); }
1541 inline IOBuf::Iterator IOBuf::end() const { return cend(); }
1543 } // namespace folly