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 <class T, class Enable=void> struct IsUniquePtrToSL
215 : public std::false_type { };
216 template <class T, class D>
217 struct IsUniquePtrToSL<
218 std::unique_ptr<T, D>,
219 typename std::enable_if<std::is_standard_layout<T>::value>::type>
220 : public std::true_type { };
221 } // namespace detail
227 enum CreateOp { CREATE };
228 enum WrapBufferOp { WRAP_BUFFER };
229 enum TakeOwnershipOp { TAKE_OWNERSHIP };
230 enum CopyBufferOp { COPY_BUFFER };
232 typedef ByteRange value_type;
233 typedef Iterator iterator;
234 typedef Iterator const_iterator;
236 typedef void (*FreeFunction)(void* buf, void* userData);
239 * Allocate a new IOBuf object with the requested capacity.
241 * Returns a new IOBuf object that must be (eventually) deleted by the
242 * caller. The returned IOBuf may actually have slightly more capacity than
245 * The data pointer will initially point to the start of the newly allocated
246 * buffer, and will have a data length of 0.
248 * Throws std::bad_alloc on error.
250 static std::unique_ptr<IOBuf> create(uint64_t capacity);
251 IOBuf(CreateOp, uint64_t capacity);
254 * Create a new IOBuf, using a single memory allocation to allocate space
255 * for both the IOBuf object and the data storage space.
257 * This saves one memory allocation. However, it can be wasteful if you
258 * later need to grow the buffer using reserve(). If the buffer needs to be
259 * reallocated, the space originally allocated will not be freed() until the
260 * IOBuf object itself is also freed. (It can also be slightly wasteful in
261 * some cases where you clone this IOBuf and then free the original IOBuf.)
263 static std::unique_ptr<IOBuf> createCombined(uint64_t capacity);
266 * Create a new IOBuf, using separate memory allocations for the IOBuf object
267 * for the IOBuf and the data storage space.
269 * This requires two memory allocations, but saves space in the long run
270 * if you know that you will need to reallocate the data buffer later.
272 static std::unique_ptr<IOBuf> createSeparate(uint64_t capacity);
275 * Allocate a new IOBuf chain with the requested total capacity, allocating
276 * no more than maxBufCapacity to each buffer.
278 static std::unique_ptr<IOBuf> createChain(
279 size_t totalCapacity, uint64_t maxBufCapacity);
282 * Create a new IOBuf pointing to an existing data buffer.
284 * The new IOBuffer will assume ownership of the buffer, and free it by
285 * calling the specified FreeFunction when the last IOBuf pointing to this
286 * buffer is destroyed. The function will be called with a pointer to the
287 * buffer as the first argument, and the supplied userData value as the
288 * second argument. The free function must never throw exceptions.
290 * If no FreeFunction is specified, the buffer will be freed using free()
291 * which will result in undefined behavior if the memory was allocated
294 * The IOBuf data pointer will initially point to the start of the buffer,
296 * In the first version of this function, the length of data is unspecified
297 * and is initialized to the capacity of the buffer
299 * In the second version, the user specifies the valid length of data
302 * On error, std::bad_alloc will be thrown. If freeOnError is true (the
303 * default) the buffer will be freed before throwing the error.
305 static std::unique_ptr<IOBuf> takeOwnership(void* buf, uint64_t capacity,
306 FreeFunction freeFn = nullptr,
307 void* userData = nullptr,
308 bool freeOnError = true) {
309 return takeOwnership(buf, capacity, capacity, freeFn,
310 userData, freeOnError);
312 IOBuf(TakeOwnershipOp op, void* buf, uint64_t capacity,
313 FreeFunction freeFn = nullptr, void* userData = nullptr,
314 bool freeOnError = true)
315 : IOBuf(op, buf, capacity, capacity, freeFn, userData, freeOnError) {}
317 static std::unique_ptr<IOBuf> takeOwnership(void* buf, uint64_t capacity,
319 FreeFunction freeFn = nullptr,
320 void* userData = nullptr,
321 bool freeOnError = true);
322 IOBuf(TakeOwnershipOp, void* buf, uint64_t capacity, uint64_t length,
323 FreeFunction freeFn = nullptr, void* userData = nullptr,
324 bool freeOnError = true);
327 * Create a new IOBuf pointing to an existing data buffer made up of
328 * count objects of a given standard-layout type.
330 * This is dangerous -- it is essentially equivalent to doing
331 * reinterpret_cast<unsigned char*> on your data -- but it's often useful
332 * for serialization / deserialization.
334 * The new IOBuffer will assume ownership of the buffer, and free it
335 * appropriately (by calling the UniquePtr's custom deleter, or by calling
336 * delete or delete[] appropriately if there is no custom deleter)
337 * when the buffer is destroyed. The custom deleter, if any, must never
340 * The IOBuf data pointer will initially point to the start of the buffer,
341 * and the length will be the full capacity of the buffer (count *
344 * On error, std::bad_alloc will be thrown, and the buffer will be freed
345 * before throwing the error.
347 template <class UniquePtr>
348 static typename std::enable_if<detail::IsUniquePtrToSL<UniquePtr>::value,
349 std::unique_ptr<IOBuf>>::type
350 takeOwnership(UniquePtr&& buf, size_t count=1);
353 * Create a new IOBuf object that points to an existing user-owned buffer.
355 * This should only be used when the caller knows the lifetime of the IOBuf
356 * object ahead of time and can ensure that all IOBuf objects that will point
357 * to this buffer will be destroyed before the buffer itself is destroyed.
359 * This buffer will not be freed automatically when the last IOBuf
360 * referencing it is destroyed. It is the caller's responsibility to free
361 * the buffer after the last IOBuf has been destroyed.
363 * The IOBuf data pointer will initially point to the start of the buffer,
364 * and the length will be the full capacity of the buffer.
366 * An IOBuf created using wrapBuffer() will always be reported as shared.
367 * unshare() may be used to create a writable copy of the buffer.
369 * On error, std::bad_alloc will be thrown.
371 static std::unique_ptr<IOBuf> wrapBuffer(const void* buf, uint64_t capacity);
372 static std::unique_ptr<IOBuf> wrapBuffer(ByteRange br) {
373 return wrapBuffer(br.data(), br.size());
377 * Similar to wrapBuffer(), but returns IOBuf by value rather than
378 * heap-allocating it.
380 static IOBuf wrapBufferAsValue(const void* buf, uint64_t capacity);
381 static IOBuf wrapBufferAsValue(ByteRange br) {
382 return wrapBufferAsValue(br.data(), br.size());
385 IOBuf(WrapBufferOp op, const void* buf, uint64_t capacity);
386 IOBuf(WrapBufferOp op, ByteRange br);
389 * Convenience function to create a new IOBuf object that copies data from a
390 * user-supplied buffer, optionally allocating a given amount of
391 * headroom and tailroom.
393 static std::unique_ptr<IOBuf> copyBuffer(const void* buf, uint64_t size,
395 uint64_t minTailroom=0);
396 static std::unique_ptr<IOBuf> copyBuffer(ByteRange br,
398 uint64_t minTailroom=0) {
399 return copyBuffer(br.data(), br.size(), headroom, minTailroom);
401 IOBuf(CopyBufferOp op, const void* buf, uint64_t size,
402 uint64_t headroom=0, uint64_t minTailroom=0);
403 IOBuf(CopyBufferOp op, ByteRange br,
404 uint64_t headroom=0, uint64_t minTailroom=0);
407 * Convenience function to create a new IOBuf object that copies data from a
408 * user-supplied string, optionally allocating a given amount of
409 * headroom and tailroom.
411 * Beware when attempting to invoke this function with a constant string
412 * literal and a headroom argument: you will likely end up invoking the
413 * version of copyBuffer() above. IOBuf::copyBuffer("hello", 3) will treat
414 * the first argument as a const void*, and will invoke the version of
415 * copyBuffer() above, with the size argument of 3.
417 static std::unique_ptr<IOBuf> copyBuffer(const std::string& buf,
419 uint64_t minTailroom=0);
420 IOBuf(CopyBufferOp op, const std::string& buf,
421 uint64_t headroom=0, uint64_t minTailroom=0)
422 : IOBuf(op, buf.data(), buf.size(), headroom, minTailroom) {}
425 * A version of copyBuffer() that returns a null pointer if the input string
428 static std::unique_ptr<IOBuf> maybeCopyBuffer(const std::string& buf,
430 uint64_t minTailroom=0);
433 * Convenience function to free a chain of IOBufs held by a unique_ptr.
435 static void destroy(std::unique_ptr<IOBuf>&& data) {
436 auto destroyer = std::move(data);
440 * Destroy this IOBuf.
442 * Deleting an IOBuf will automatically destroy all IOBufs in the chain.
443 * (See the comments above regarding the ownership model of IOBuf chains.
444 * All subsequent IOBufs in the chain are considered to be owned by the head
445 * of the chain. Users should only explicitly delete the head of a chain.)
447 * When each individual IOBuf is destroyed, it will release its reference
448 * count on the underlying buffer. If it was the last user of the buffer,
449 * the buffer will be freed.
454 * Check whether the chain is empty (i.e., whether the IOBufs in the
455 * chain have a total data length of zero).
457 * This method is semantically equivalent to
458 * i->computeChainDataLength()==0
459 * but may run faster because it can short-circuit as soon as it
460 * encounters a buffer with length()!=0
465 * Get the pointer to the start of the data.
467 const uint8_t* data() const {
472 * Get a writable pointer to the start of the data.
474 * The caller is responsible for calling unshare() first to ensure that it is
475 * actually safe to write to the buffer.
477 uint8_t* writableData() {
482 * Get the pointer to the end of the data.
484 const uint8_t* tail() const {
485 return data_ + length_;
489 * Get a writable pointer to the end of the data.
491 * The caller is responsible for calling unshare() first to ensure that it is
492 * actually safe to write to the buffer.
494 uint8_t* writableTail() {
495 return data_ + length_;
499 * Get the data length.
501 uint64_t length() const {
506 * Get the amount of head room.
508 * Returns the number of bytes in the buffer before the start of the data.
510 uint64_t headroom() const {
511 return uint64_t(data_ - buffer());
515 * Get the amount of tail room.
517 * Returns the number of bytes in the buffer after the end of the data.
519 uint64_t tailroom() const {
520 return uint64_t(bufferEnd() - tail());
524 * Get the pointer to the start of the buffer.
526 * Note that this is the pointer to the very beginning of the usable buffer,
527 * not the start of valid data within the buffer. Use the data() method to
528 * get a pointer to the start of the data within the buffer.
530 const uint8_t* buffer() const {
535 * Get a writable pointer to the start of the buffer.
537 * The caller is responsible for calling unshare() first to ensure that it is
538 * actually safe to write to the buffer.
540 uint8_t* writableBuffer() {
545 * Get the pointer to the end of the buffer.
547 * Note that this is the pointer to the very end of the usable buffer,
548 * not the end of valid data within the buffer. Use the tail() method to
549 * get a pointer to the end of the data within the buffer.
551 const uint8_t* bufferEnd() const {
552 return buf_ + capacity_;
556 * Get the total size of the buffer.
558 * This returns the total usable length of the buffer. Use the length()
559 * method to get the length of the actual valid data in this IOBuf.
561 uint64_t capacity() const {
566 * Get a pointer to the next IOBuf in this chain.
571 const IOBuf* next() const {
576 * Get a pointer to the previous IOBuf in this chain.
581 const IOBuf* prev() const {
586 * Shift the data forwards in the buffer.
588 * This shifts the data pointer forwards in the buffer to increase the
589 * headroom. This is commonly used to increase the headroom in a newly
592 * The caller is responsible for ensuring that there is sufficient
593 * tailroom in the buffer before calling advance().
595 * If there is a non-zero data length, advance() will use memmove() to shift
596 * the data forwards in the buffer. In this case, the caller is responsible
597 * for making sure the buffer is unshared, so it will not affect other IOBufs
598 * that may be sharing the same underlying buffer.
600 void advance(uint64_t amount) {
601 // In debug builds, assert if there is a problem.
602 assert(amount <= tailroom());
605 memmove(data_ + amount, data_, length_);
611 * Shift the data backwards in the buffer.
613 * The caller is responsible for ensuring that there is sufficient headroom
614 * in the buffer before calling retreat().
616 * If there is a non-zero data length, retreat() will use memmove() to shift
617 * the data backwards in the buffer. In this case, the caller is responsible
618 * for making sure the buffer is unshared, so it will not affect other IOBufs
619 * that may be sharing the same underlying buffer.
621 void retreat(uint64_t amount) {
622 // In debug builds, assert if there is a problem.
623 assert(amount <= headroom());
626 memmove(data_ - amount, data_, length_);
632 * Adjust the data pointer to include more valid data at the beginning.
634 * This moves the data pointer backwards to include more of the available
635 * buffer. The caller is responsible for ensuring that there is sufficient
636 * headroom for the new data. The caller is also responsible for populating
637 * this section with valid data.
639 * This does not modify any actual data in the buffer.
641 void prepend(uint64_t amount) {
642 DCHECK_LE(amount, headroom());
648 * Adjust the tail pointer to include more valid data at the end.
650 * This moves the tail pointer forwards to include more of the available
651 * buffer. The caller is responsible for ensuring that there is sufficient
652 * tailroom for the new data. The caller is also responsible for populating
653 * this section with valid data.
655 * This does not modify any actual data in the buffer.
657 void append(uint64_t amount) {
658 DCHECK_LE(amount, tailroom());
663 * Adjust the data pointer forwards to include less valid data.
665 * This moves the data pointer forwards so that the first amount bytes are no
666 * longer considered valid data. The caller is responsible for ensuring that
667 * amount is less than or equal to the actual data length.
669 * This does not modify any actual data in the buffer.
671 void trimStart(uint64_t amount) {
672 DCHECK_LE(amount, length_);
678 * Adjust the tail pointer backwards to include less valid data.
680 * This moves the tail pointer backwards so that the last amount bytes are no
681 * longer considered valid data. The caller is responsible for ensuring that
682 * amount is less than or equal to the actual data length.
684 * This does not modify any actual data in the buffer.
686 void trimEnd(uint64_t amount) {
687 DCHECK_LE(amount, length_);
694 * Postcondition: headroom() == 0, length() == 0, tailroom() == capacity()
697 data_ = writableBuffer();
702 * Ensure that this buffer has at least minHeadroom headroom bytes and at
703 * least minTailroom tailroom bytes. The buffer must be writable
704 * (you must call unshare() before this, if necessary).
706 * Postcondition: headroom() >= minHeadroom, tailroom() >= minTailroom,
707 * the data (between data() and data() + length()) is preserved.
709 void reserve(uint64_t minHeadroom, uint64_t minTailroom) {
710 // Maybe we don't need to do anything.
711 if (headroom() >= minHeadroom && tailroom() >= minTailroom) {
714 // If the buffer is empty but we have enough total room (head + tail),
715 // move the data_ pointer around.
717 headroom() + tailroom() >= minHeadroom + minTailroom) {
718 data_ = writableBuffer() + minHeadroom;
721 // Bah, we have to do actual work.
722 reserveSlow(minHeadroom, minTailroom);
726 * Return true if this IOBuf is part of a chain of multiple IOBufs, or false
727 * if this is the only IOBuf in its chain.
729 bool isChained() const {
730 assert((next_ == this) == (prev_ == this));
731 return next_ != this;
735 * Get the number of IOBufs in this chain.
737 * Beware that this method has to walk the entire chain.
738 * Use isChained() if you just want to check if this IOBuf is part of a chain
741 size_t countChainElements() const;
744 * Get the length of all the data in this IOBuf chain.
746 * Beware that this method has to walk the entire chain.
748 uint64_t computeChainDataLength() const;
751 * Insert another IOBuf chain immediately before this IOBuf.
753 * For example, if there are two IOBuf chains (A, B, C) and (D, E, F),
754 * and B->prependChain(D) is called, the (D, E, F) chain will be subsumed
755 * and become part of the chain starting at A, which will now look like
758 * Note that since IOBuf chains are circular, head->prependChain(other) can
759 * be used to append the other chain at the very end of the chain pointed to
760 * by head. For example, if there are two IOBuf chains (A, B, C) and
761 * (D, E, F), and A->prependChain(D) is called, the chain starting at A will
762 * now consist of (A, B, C, D, E, F)
764 * The elements in the specified IOBuf chain will become part of this chain,
765 * and will be owned by the head of this chain. When this chain is
766 * destroyed, all elements in the supplied chain will also be destroyed.
768 * For this reason, appendChain() only accepts an rvalue-reference to a
769 * unique_ptr(), to make it clear that it is taking ownership of the supplied
770 * chain. If you have a raw pointer, you can pass in a new temporary
771 * unique_ptr around the raw pointer. If you have an existing,
772 * non-temporary unique_ptr, you must call std::move(ptr) to make it clear
773 * that you are destroying the original pointer.
775 void prependChain(std::unique_ptr<IOBuf>&& iobuf);
778 * Append another IOBuf chain immediately after this IOBuf.
780 * For example, if there are two IOBuf chains (A, B, C) and (D, E, F),
781 * and B->appendChain(D) is called, the (D, E, F) chain will be subsumed
782 * and become part of the chain starting at A, which will now look like
785 * The elements in the specified IOBuf chain will become part of this chain,
786 * and will be owned by the head of this chain. When this chain is
787 * destroyed, all elements in the supplied chain will also be destroyed.
789 * For this reason, appendChain() only accepts an rvalue-reference to a
790 * unique_ptr(), to make it clear that it is taking ownership of the supplied
791 * chain. If you have a raw pointer, you can pass in a new temporary
792 * unique_ptr around the raw pointer. If you have an existing,
793 * non-temporary unique_ptr, you must call std::move(ptr) to make it clear
794 * that you are destroying the original pointer.
796 void appendChain(std::unique_ptr<IOBuf>&& iobuf) {
797 // Just use prependChain() on the next element in our chain
798 next_->prependChain(std::move(iobuf));
802 * Remove this IOBuf from its current chain.
804 * Since ownership of all elements an IOBuf chain is normally maintained by
805 * the head of the chain, unlink() transfers ownership of this IOBuf from the
806 * chain and gives it to the caller. A new unique_ptr to the IOBuf is
807 * returned to the caller. The caller must store the returned unique_ptr (or
808 * call release() on it) to take ownership, otherwise the IOBuf will be
809 * immediately destroyed.
811 * Since unlink transfers ownership of the IOBuf to the caller, be careful
812 * not to call unlink() on the head of a chain if you already maintain
813 * ownership on the head of the chain via other means. The pop() method
814 * is a better choice for that situation.
816 std::unique_ptr<IOBuf> unlink() {
817 next_->prev_ = prev_;
818 prev_->next_ = next_;
821 return std::unique_ptr<IOBuf>(this);
825 * Remove this IOBuf from its current chain and return a unique_ptr to
826 * the IOBuf that formerly followed it in the chain.
828 std::unique_ptr<IOBuf> pop() {
830 next_->prev_ = prev_;
831 prev_->next_ = next_;
834 return std::unique_ptr<IOBuf>((next == this) ? nullptr : next);
838 * Remove a subchain from this chain.
840 * Remove the subchain starting at head and ending at tail from this chain.
842 * Returns a unique_ptr pointing to head. (In other words, ownership of the
843 * head of the subchain is transferred to the caller.) If the caller ignores
844 * the return value and lets the unique_ptr be destroyed, the subchain will
845 * be immediately destroyed.
847 * The subchain referenced by the specified head and tail must be part of the
848 * same chain as the current IOBuf, but must not contain the current IOBuf.
849 * However, the specified head and tail may be equal to each other (i.e.,
850 * they may be a subchain of length 1).
852 std::unique_ptr<IOBuf> separateChain(IOBuf* head, IOBuf* tail) {
853 assert(head != this);
854 assert(tail != this);
856 head->prev_->next_ = tail->next_;
857 tail->next_->prev_ = head->prev_;
862 return std::unique_ptr<IOBuf>(head);
866 * Return true if at least one of the IOBufs in this chain are shared,
867 * or false if all of the IOBufs point to unique buffers.
869 * Use isSharedOne() to only check this IOBuf rather than the entire chain.
871 bool isShared() const {
872 const IOBuf* current = this;
874 if (current->isSharedOne()) {
877 current = current->next_;
878 if (current == this) {
885 * Return true if all IOBufs in this chain are managed by the usual
886 * refcounting mechanism (and so the lifetime of the underlying memory
887 * can be extended by clone()).
889 bool isManaged() const {
890 const IOBuf* current = this;
892 if (!current->isManagedOne()) {
895 current = current->next_;
896 if (current == this) {
903 * Return true if this IOBuf is managed by the usual refcounting mechanism
904 * (and so the lifetime of the underlying memory can be extended by
907 bool isManagedOne() const {
912 * Return true if other IOBufs are also pointing to the buffer used by this
913 * IOBuf, and false otherwise.
915 * If this IOBuf points at a buffer owned by another (non-IOBuf) part of the
916 * code (i.e., if the IOBuf was created using wrapBuffer(), or was cloned
917 * from such an IOBuf), it is always considered shared.
919 * This only checks the current IOBuf, and not other IOBufs in the chain.
921 bool isSharedOne() const {
922 // If this is a user-owned buffer, it is always considered shared
923 if (UNLIKELY(!sharedInfo())) {
927 if (UNLIKELY(sharedInfo()->externallyShared)) {
931 if (LIKELY(!(flags() & kFlagMaybeShared))) {
935 // kFlagMaybeShared is set, so we need to check the reference count.
936 // (Checking the reference count requires an atomic operation, which is why
937 // we prefer to only check kFlagMaybeShared if possible.)
938 bool shared = sharedInfo()->refcount.load(std::memory_order_acquire) > 1;
940 // we're the last one left
941 clearFlags(kFlagMaybeShared);
947 * Ensure that this IOBuf has a unique buffer that is not shared by other
950 * unshare() operates on an entire chain of IOBuf objects. If the chain is
951 * shared, it may also coalesce the chain when making it unique. If the
952 * chain is coalesced, subsequent IOBuf objects in the current chain will be
953 * automatically deleted.
955 * Note that buffers owned by other (non-IOBuf) users are automatically
958 * Throws std::bad_alloc on error. On error the IOBuf chain will be
961 * Currently unshare may also throw std::overflow_error if it tries to
962 * coalesce. (TODO: In the future it would be nice if unshare() were smart
963 * enough not to coalesce the entire buffer if the data is too large.
964 * However, in practice this seems unlikely to become an issue.)
975 * Ensure that this IOBuf has a unique buffer that is not shared by other
978 * unshareOne() operates on a single IOBuf object. This IOBuf will have a
979 * unique buffer after unshareOne() returns, but other IOBufs in the chain
980 * may still be shared after unshareOne() returns.
982 * Throws std::bad_alloc on error. On error the IOBuf will be unmodified.
991 * Mark the underlying buffers in this chain as shared with external memory
992 * management mechanism. This will make isShared() always returns true.
994 * This function is not thread-safe, and only safe to call immediately after
995 * creating an IOBuf, before it has been shared with other threads.
997 void markExternallyShared();
1000 * Mark the underlying buffer that this IOBuf refers to as shared with
1001 * external memory management mechanism. This will make isSharedOne() always
1004 * This function is not thread-safe, and only safe to call immediately after
1005 * creating an IOBuf, before it has been shared with other threads.
1007 void markExternallySharedOne() {
1008 SharedInfo* info = sharedInfo();
1010 info->externallyShared = true;
1015 * Ensure that the memory that IOBufs in this chain refer to will continue to
1016 * be allocated for as long as the IOBufs of the chain (or any clone()s
1017 * created from this point onwards) is alive.
1019 * This only has an effect for user-owned buffers (created with the
1020 * WRAP_BUFFER constructor or wrapBuffer factory function), in which case
1021 * those buffers are unshared.
1023 void makeManaged() {
1025 makeManagedChained();
1032 * Ensure that the memory that this IOBuf refers to will continue to be
1033 * allocated for as long as this IOBuf (or any clone()s created from this
1034 * point onwards) is alive.
1036 * This only has an effect for user-owned buffers (created with the
1037 * WRAP_BUFFER constructor or wrapBuffer factory function), in which case
1038 * those buffers are unshared.
1040 void makeManagedOne() {
1041 if (!isManagedOne()) {
1042 // We can call the internal function directly; unmanaged implies shared.
1048 * Coalesce this IOBuf chain into a single buffer.
1050 * This method moves all of the data in this IOBuf chain into a single
1051 * contiguous buffer, if it is not already in one buffer. After coalesce()
1052 * returns, this IOBuf will be a chain of length one. Other IOBufs in the
1053 * chain will be automatically deleted.
1055 * After coalescing, the IOBuf will have at least as much headroom as the
1056 * first IOBuf in the chain, and at least as much tailroom as the last IOBuf
1059 * Throws std::bad_alloc on error. On error the IOBuf chain will be
1062 * Returns ByteRange that points to the data IOBuf stores.
1064 ByteRange coalesce() {
1068 return ByteRange(data_, length_);
1072 * Ensure that this chain has at least maxLength bytes available as a
1073 * contiguous memory range.
1075 * This method coalesces whole buffers in the chain into this buffer as
1076 * necessary until this buffer's length() is at least maxLength.
1078 * After coalescing, the IOBuf will have at least as much headroom as the
1079 * first IOBuf in the chain, and at least as much tailroom as the last IOBuf
1080 * that was coalesced.
1082 * Throws std::bad_alloc or std::overflow_error on error. On error the IOBuf
1083 * chain will be unmodified. Throws std::overflow_error if maxLength is
1084 * longer than the total chain length.
1086 * Upon return, either enough of the chain was coalesced into a contiguous
1087 * region, or the entire chain was coalesced. That is,
1088 * length() >= maxLength || !isChained() is true.
1090 void gather(uint64_t maxLength) {
1091 if (!isChained() || length_ >= maxLength) {
1094 coalesceSlow(maxLength);
1098 * Return a new IOBuf chain sharing the same data as this chain.
1100 * The new IOBuf chain will normally point to the same underlying data
1101 * buffers as the original chain. (The one exception to this is if some of
1102 * the IOBufs in this chain contain small internal data buffers which cannot
1105 std::unique_ptr<IOBuf> clone() const;
1108 * Similar to clone(). But returns IOBuf by value rather than heap-allocating
1111 IOBuf cloneAsValue() const;
1114 * Return a new IOBuf with the same data as this IOBuf.
1116 * The new IOBuf returned will not be part of a chain (even if this IOBuf is
1117 * part of a larger chain).
1119 std::unique_ptr<IOBuf> cloneOne() const;
1122 * Similar to cloneOne(). But returns IOBuf by value rather than
1123 * heap-allocating it.
1125 IOBuf cloneOneAsValue() const;
1128 * Return a new unchained IOBuf that may share the same data as this chain.
1130 * If the IOBuf chain is not chained then the new IOBuf will point to the same
1131 * underlying data buffer as the original chain. Otherwise, it will clone and
1132 * coalesce the IOBuf chain.
1134 * The new IOBuf will have at least as much headroom as the first IOBuf in the
1135 * chain, and at least as much tailroom as the last IOBuf in the chain.
1137 * Throws std::bad_alloc on error.
1139 std::unique_ptr<IOBuf> cloneCoalesced() const;
1142 * Similar to cloneCoalesced(). But returns IOBuf by value rather than
1143 * heap-allocating it.
1145 IOBuf cloneCoalescedAsValue() const;
1148 * Similar to Clone(). But use other as the head node. Other nodes in the
1149 * chain (if any) will be allocted on heap.
1151 void cloneInto(IOBuf& other) const {
1152 other = cloneAsValue();
1156 * Similar to CloneOne(). But to fill an existing IOBuf instead of a new
1159 void cloneOneInto(IOBuf& other) const {
1160 other = cloneOneAsValue();
1164 * Return an iovector suitable for e.g. writev()
1166 * auto iov = buf->getIov();
1167 * auto xfer = writev(fd, iov.data(), iov.size());
1169 * Naturally, the returned iovector is invalid if you modify the buffer
1172 folly::fbvector<struct iovec> getIov() const;
1175 * Update an existing iovec array with the IOBuf data.
1177 * New iovecs will be appended to the existing vector; anything already
1178 * present in the vector will be left unchanged.
1180 * Naturally, the returned iovec data will be invalid if you modify the
1183 void appendToIov(folly::fbvector<struct iovec>* iov) const;
1186 * Fill an iovec array with the IOBuf data.
1188 * Returns the number of iovec filled. If there are more buffer than
1189 * iovec, returns 0. This version is suitable to use with stack iovec
1192 * Naturally, the filled iovec data will be invalid if you modify the
1195 size_t fillIov(struct iovec* iov, size_t len) const;
1198 * Overridden operator new and delete.
1199 * These perform specialized memory management to help support
1200 * createCombined(), which allocates IOBuf objects together with the buffer
1203 void* operator new(size_t size);
1204 void* operator new(size_t size, void* ptr);
1205 void operator delete(void* ptr);
1208 * Destructively convert this IOBuf to a fbstring efficiently.
1209 * We rely on fbstring's AcquireMallocatedString constructor to
1212 fbstring moveToFbString();
1215 * Iteration support: a chain of IOBufs may be iterated through using
1216 * STL-style iterators over const ByteRanges. Iterators are only invalidated
1217 * if the IOBuf that they currently point to is removed.
1219 Iterator cbegin() const;
1220 Iterator cend() const;
1221 Iterator begin() const;
1222 Iterator end() const;
1225 * Allocate a new null buffer.
1227 * This can be used to allocate an empty IOBuf on the stack. It will have no
1228 * space allocated for it. This is generally useful only to later use move
1229 * assignment to fill out the IOBuf.
1234 * Move constructor and assignment operator.
1236 * In general, you should only ever move the head of an IOBuf chain.
1237 * Internal nodes in an IOBuf chain are owned by the head of the chain, and
1238 * should not be moved from. (Technically, nothing prevents you from moving
1239 * a non-head node, but the moved-to node will replace the moved-from node in
1240 * the chain. This has implications for ownership, since non-head nodes are
1241 * owned by the chain head. You are then responsible for relinquishing
1242 * ownership of the moved-to node, and manually deleting the moved-from
1245 * With the move assignment operator, the destination of the move should be
1246 * the head of an IOBuf chain or a solitary IOBuf not part of a chain. If
1247 * the move destination is part of a chain, all other IOBufs in the chain
1250 IOBuf(IOBuf&& other) noexcept;
1251 IOBuf& operator=(IOBuf&& other) noexcept;
1253 IOBuf(const IOBuf& other);
1254 IOBuf& operator=(const IOBuf& other);
1257 enum FlagsEnum : uintptr_t {
1258 // Adding any more flags would not work on 32-bit architectures,
1259 // as these flags are stashed in the least significant 2 bits of a
1260 // max-align-aligned pointer.
1261 kFlagFreeSharedInfo = 0x1,
1262 kFlagMaybeShared = 0x2,
1263 kFlagMask = kFlagFreeSharedInfo | kFlagMaybeShared
1268 SharedInfo(FreeFunction fn, void* arg);
1270 // A pointer to a function to call to free the buffer when the refcount
1271 // hits 0. If this is null, free() will be used instead.
1272 FreeFunction freeFn;
1274 std::atomic<uint32_t> refcount;
1275 bool externallyShared{false};
1277 // Helper structs for use by operator new and delete
1280 struct HeapFullStorage;
1283 * Create a new IOBuf pointing to an external buffer.
1285 * The caller is responsible for holding a reference count for this new
1286 * IOBuf. The IOBuf constructor does not automatically increment the
1289 struct InternalConstructor {}; // avoid conflicts
1290 IOBuf(InternalConstructor, uintptr_t flagsAndSharedInfo,
1291 uint8_t* buf, uint64_t capacity,
1292 uint8_t* data, uint64_t length);
1294 void unshareOneSlow();
1295 void unshareChained();
1296 void makeManagedChained();
1297 void coalesceSlow();
1298 void coalesceSlow(size_t maxLength);
1299 // newLength must be the entire length of the buffers between this and
1300 // end (no truncation)
1301 void coalesceAndReallocate(
1305 size_t newTailroom);
1306 void coalesceAndReallocate(size_t newLength, IOBuf* end) {
1307 coalesceAndReallocate(headroom(), newLength, end, end->prev_->tailroom());
1309 void decrementRefcount();
1310 void reserveSlow(uint64_t minHeadroom, uint64_t minTailroom);
1311 void freeExtBuffer();
1313 static size_t goodExtBufferSize(uint64_t minCapacity);
1314 static void initExtBuffer(uint8_t* buf, size_t mallocSize,
1315 SharedInfo** infoReturn,
1316 uint64_t* capacityReturn);
1317 static void allocExtBuffer(uint64_t minCapacity,
1318 uint8_t** bufReturn,
1319 SharedInfo** infoReturn,
1320 uint64_t* capacityReturn);
1321 static void releaseStorage(HeapStorage* storage, uint16_t freeFlags);
1322 static void freeInternalBuf(void* buf, void* userData);
1329 * Links to the next and the previous IOBuf in this chain.
1331 * The chain is circularly linked (the last element in the chain points back
1332 * at the head), and next_ and prev_ can never be null. If this IOBuf is the
1333 * only element in the chain, next_ and prev_ will both point to this.
1339 * A pointer to the start of the data referenced by this IOBuf, and the
1340 * length of the data.
1342 * This may refer to any subsection of the actual buffer capacity.
1344 uint8_t* data_{nullptr};
1345 uint8_t* buf_{nullptr};
1346 uint64_t length_{0};
1347 uint64_t capacity_{0};
1349 // Pack flags in least significant 2 bits, sharedInfo in the rest
1350 mutable uintptr_t flagsAndSharedInfo_{0};
1352 static inline uintptr_t packFlagsAndSharedInfo(uintptr_t flags,
1354 uintptr_t uinfo = reinterpret_cast<uintptr_t>(info);
1355 DCHECK_EQ(flags & ~kFlagMask, 0u);
1356 DCHECK_EQ(uinfo & kFlagMask, 0u);
1357 return flags | uinfo;
1360 inline SharedInfo* sharedInfo() const {
1361 return reinterpret_cast<SharedInfo*>(flagsAndSharedInfo_ & ~kFlagMask);
1364 inline void setSharedInfo(SharedInfo* info) {
1365 uintptr_t uinfo = reinterpret_cast<uintptr_t>(info);
1366 DCHECK_EQ(uinfo & kFlagMask, 0u);
1367 flagsAndSharedInfo_ = (flagsAndSharedInfo_ & kFlagMask) | uinfo;
1370 inline uintptr_t flags() const {
1371 return flagsAndSharedInfo_ & kFlagMask;
1374 // flags_ are changed from const methods
1375 inline void setFlags(uintptr_t flags) const {
1376 DCHECK_EQ(flags & ~kFlagMask, 0u);
1377 flagsAndSharedInfo_ |= flags;
1380 inline void clearFlags(uintptr_t flags) const {
1381 DCHECK_EQ(flags & ~kFlagMask, 0u);
1382 flagsAndSharedInfo_ &= ~flags;
1385 inline void setFlagsAndSharedInfo(uintptr_t flags, SharedInfo* info) {
1386 flagsAndSharedInfo_ = packFlagsAndSharedInfo(flags, info);
1389 struct DeleterBase {
1390 virtual ~DeleterBase() { }
1391 virtual void dispose(void* p) = 0;
1394 template <class UniquePtr>
1395 struct UniquePtrDeleter : public DeleterBase {
1396 typedef typename UniquePtr::pointer Pointer;
1397 typedef typename UniquePtr::deleter_type Deleter;
1399 explicit UniquePtrDeleter(Deleter deleter) : deleter_(std::move(deleter)){ }
1400 void dispose(void* p) override {
1402 deleter_(static_cast<Pointer>(p));
1413 static void freeUniquePtrBuffer(void* ptr, void* userData) {
1414 static_cast<DeleterBase*>(userData)->dispose(ptr);
1419 * Hasher for IOBuf objects. Hashes the entire chain using SpookyHashV2.
1422 size_t operator()(const IOBuf& buf) const;
1423 size_t operator()(const std::unique_ptr<IOBuf>& buf) const {
1424 return buf ? (*this)(*buf) : 0;
1429 * Equality predicate for IOBuf objects. Compares data in the entire chain.
1432 bool operator()(const IOBuf& a, const IOBuf& b) const;
1433 bool operator()(const std::unique_ptr<IOBuf>& a,
1434 const std::unique_ptr<IOBuf>& b) const {
1437 } else if (!a || !b) {
1440 return (*this)(*a, *b);
1445 template <class UniquePtr>
1446 typename std::enable_if<detail::IsUniquePtrToSL<UniquePtr>::value,
1447 std::unique_ptr<IOBuf>>::type
1448 IOBuf::takeOwnership(UniquePtr&& buf, size_t count) {
1449 size_t size = count * sizeof(typename UniquePtr::element_type);
1450 auto deleter = new UniquePtrDeleter<UniquePtr>(buf.get_deleter());
1451 return takeOwnership(buf.release(),
1453 &IOBuf::freeUniquePtrBuffer,
1457 inline std::unique_ptr<IOBuf> IOBuf::copyBuffer(
1458 const void* data, uint64_t size, uint64_t headroom,
1459 uint64_t minTailroom) {
1460 uint64_t capacity = headroom + size + minTailroom;
1461 std::unique_ptr<IOBuf> buf = create(capacity);
1462 buf->advance(headroom);
1464 memcpy(buf->writableData(), data, size);
1470 inline std::unique_ptr<IOBuf> IOBuf::copyBuffer(const std::string& buf,
1472 uint64_t minTailroom) {
1473 return copyBuffer(buf.data(), buf.size(), headroom, minTailroom);
1476 inline std::unique_ptr<IOBuf> IOBuf::maybeCopyBuffer(const std::string& buf,
1478 uint64_t minTailroom) {
1482 return copyBuffer(buf.data(), buf.size(), headroom, minTailroom);
1485 class IOBuf::Iterator : public boost::iterator_facade<
1486 IOBuf::Iterator, // Derived
1487 const ByteRange, // Value
1488 boost::forward_traversal_tag // Category or traversal
1490 friend class boost::iterator_core_access;
1492 // Note that IOBufs are stored as a circular list without a guard node,
1493 // so pos == end is ambiguous (it may mean "begin" or "end"). To solve
1494 // the ambiguity (at the cost of one extra comparison in the "increment"
1495 // code path), we define end iterators as having pos_ == end_ == nullptr
1496 // and we only allow forward iteration.
1497 explicit Iterator(const IOBuf* pos, const IOBuf* end)
1500 // Sadly, we must return by const reference, not by value.
1510 val_ = ByteRange(pos_->data(), pos_->tail());
1513 void adjustForEnd() {
1515 pos_ = end_ = nullptr;
1522 const ByteRange& dereference() const {
1526 bool equal(const Iterator& other) const {
1527 // We must compare end_ in addition to pos_, because forward traversal
1528 // requires that if two iterators are equal (a == b) and dereferenceable,
1530 return pos_ == other.pos_ && end_ == other.end_;
1534 pos_ = pos_->next();
1538 const IOBuf* pos_{nullptr};
1539 const IOBuf* end_{nullptr};
1543 inline IOBuf::Iterator IOBuf::begin() const { return cbegin(); }
1544 inline IOBuf::Iterator IOBuf::end() const { return cend(); }
1546 } // namespace folly