using std::unique_ptr;
+namespace {
+
+enum : uint16_t {
+ kHeapMagic = 0xa5a5,
+ // This memory segment contains an IOBuf that is still in use
+ kIOBufInUse = 0x01,
+ // This memory segment contains buffer data that is still in use
+ kDataInUse = 0x02,
+};
+
+enum : uint32_t {
+ // When create() is called for buffers less than kDefaultCombinedBufSize,
+ // we allocate a single combined memory segment for the IOBuf and the data
+ // together. See the comments for createCombined()/createSeparate() for more
+ // details.
+ //
+ // (The size of 1k is largely just a guess here. We could could probably do
+ // benchmarks of real applications to see if adjusting this number makes a
+ // difference. Callers that know their exact use case can also explicitly
+ // call createCombined() or createSeparate().)
+ kDefaultCombinedBufSize = 1024
+};
+
+}
+
namespace folly {
-const uint32_t IOBuf::kMaxIOBufSize;
-// Note: Applying offsetof() to an IOBuf is legal according to C++11, since
-// IOBuf is a standard-layout class. However, this isn't legal with earlier
-// C++ standards, which require that offsetof() only be used with POD types.
-//
-// This code compiles with g++ 4.6, but not with g++ 4.4 or earlier versions.
-const uint32_t IOBuf::kMaxInternalDataSize =
- kMaxIOBufSize - offsetof(folly::IOBuf, int_.buf);
+struct IOBuf::HeapPrefix {
+ HeapPrefix(uint16_t flg)
+ : magic(kHeapMagic),
+ flags(flg) {}
+ ~HeapPrefix() {
+ // Reset magic to 0 on destruction. This is solely for debugging purposes
+ // to help catch bugs where someone tries to use HeapStorage after it has
+ // been deleted.
+ magic = 0;
+ }
+
+ uint16_t magic;
+ std::atomic<uint16_t> flags;
+};
+
+struct IOBuf::HeapStorage {
+ HeapPrefix prefix;
+ // The IOBuf is last in the HeapStorage object.
+ // This way operator new will work even if allocating a subclass of IOBuf
+ // that requires more space.
+ folly::IOBuf buf;
+};
+
+struct IOBuf::HeapFullStorage {
+ HeapStorage hs;
+ SharedInfo shared;
+ MaxAlign align;
+};
IOBuf::SharedInfo::SharedInfo()
: freeFn(NULL),
}
void* IOBuf::operator new(size_t size) {
- // Since IOBuf::create() manually allocates space for some IOBuf objects
- // using malloc(), override operator new so that all IOBuf objects are
- // always allocated using malloc(). This way operator delete can always know
- // that free() is the correct way to deallocate the memory.
- void* ptr = malloc(size);
-
+ size_t fullSize = offsetof(HeapStorage, buf) + size;
+ auto* storage = static_cast<HeapStorage*>(malloc(fullSize));
// operator new is not allowed to return NULL
- if (UNLIKELY(ptr == NULL)) {
+ if (UNLIKELY(storage == nullptr)) {
throw std::bad_alloc();
}
- return ptr;
+ new (&storage->prefix) HeapPrefix(kIOBufInUse);
+ return &(storage->buf);
}
void* IOBuf::operator new(size_t size, void* ptr) {
- assert(size <= kMaxIOBufSize);
return ptr;
}
void IOBuf::operator delete(void* ptr) {
- // For small buffers, IOBuf::create() manually allocates the space for the
- // IOBuf object using malloc(). Therefore we override delete to ensure that
- // the IOBuf space is freed using free() rather than a normal delete.
- free(ptr);
+ auto* storageAddr = static_cast<uint8_t*>(ptr) - offsetof(HeapStorage, buf);
+ auto* storage = reinterpret_cast<HeapStorage*>(storageAddr);
+ releaseStorage(storage, kIOBufInUse);
}
-unique_ptr<IOBuf> IOBuf::create(uint32_t capacity) {
- // If the desired capacity is less than kMaxInternalDataSize,
- // just allocate a single region large enough for both the IOBuf header and
- // the data.
- if (capacity <= kMaxInternalDataSize) {
- void* buf = malloc(kMaxIOBufSize);
- if (UNLIKELY(buf == NULL)) {
- throw std::bad_alloc();
+void IOBuf::releaseStorage(HeapStorage* storage, uint16_t freeFlags) {
+ CHECK_EQ(storage->prefix.magic, kHeapMagic);
+
+ // Use relaxed memory order here. If we are unlucky and happen to get
+ // out-of-date data the compare_exchange_weak() call below will catch
+ // it and load new data with memory_order_acq_rel.
+ auto flags = storage->prefix.flags.load(std::memory_order_acquire);
+ DCHECK_EQ((flags & freeFlags), freeFlags);
+
+ while (true) {
+ uint16_t newFlags = (flags & ~freeFlags);
+ if (newFlags == 0) {
+ // The storage space is now unused. Free it.
+ storage->prefix.HeapPrefix::~HeapPrefix();
+ free(storage);
+ return;
+ }
+
+ // This storage segment still contains portions that are in use.
+ // Just clear the flags specified in freeFlags for now.
+ auto ret = storage->prefix.flags.compare_exchange_weak(
+ flags, newFlags, std::memory_order_acq_rel);
+ if (ret) {
+ // We successfully updated the flags.
+ return;
}
- uint8_t* bufEnd = static_cast<uint8_t*>(buf) + kMaxIOBufSize;
- unique_ptr<IOBuf> iobuf(new(buf) IOBuf(bufEnd));
- assert(iobuf->capacity() >= capacity);
- return iobuf;
+ // We failed to update the flags. Some other thread probably updated them
+ // and cleared some of the other bits. Continue around the loop to see if
+ // we are the last user now, or if we need to try updating the flags again.
+ }
+}
+
+void IOBuf::freeInternalBuf(void* buf, void* userData) {
+ auto* storage = static_cast<HeapStorage*>(userData);
+ releaseStorage(storage, kDataInUse);
+}
+
+unique_ptr<IOBuf> IOBuf::create(uint32_t capacity) {
+ // For smaller-sized buffers, allocate the IOBuf, SharedInfo, and the buffer
+ // all with a single allocation.
+ //
+ // We don't do this for larger buffers since it can be wasteful if the user
+ // needs to reallocate the buffer but keeps using the same IOBuf object.
+ // In this case we can't free the data space until the IOBuf is also
+ // destroyed. Callers can explicitly call createCombined() or
+ // createSeparate() if they know their use case better, and know if they are
+ // likely to reallocate the buffer later.
+ if (capacity <= kDefaultCombinedBufSize) {
+ return createCombined(capacity);
}
+ return createSeparate(capacity);
+}
+
+unique_ptr<IOBuf> IOBuf::createCombined(uint32_t capacity) {
+ // To save a memory allocation, allocate space for the IOBuf object, the
+ // SharedInfo struct, and the data itself all with a single call to malloc().
+ size_t requiredStorage = offsetof(HeapFullStorage, align) + capacity;
+ size_t mallocSize = goodMallocSize(requiredStorage);
+ auto* storage = static_cast<HeapFullStorage*>(malloc(mallocSize));
+
+ new (&storage->hs.prefix) HeapPrefix(kIOBufInUse | kDataInUse);
+ new (&storage->shared) SharedInfo(freeInternalBuf, storage);
+ uint8_t* bufAddr = reinterpret_cast<uint8_t*>(&storage->align);
+ uint8_t* storageEnd = reinterpret_cast<uint8_t*>(storage) + mallocSize;
+ size_t actualCapacity = storageEnd - bufAddr;
+ unique_ptr<IOBuf> ret(new (&storage->hs.buf) IOBuf(
+ kCombinedAlloc, 0, bufAddr, actualCapacity,
+ bufAddr, 0, &storage->shared));
+ return ret;
+}
+
+unique_ptr<IOBuf> IOBuf::createSeparate(uint32_t capacity) {
// Allocate an external buffer
uint8_t* buf;
SharedInfo* sharedInfo;
bool freeOnError) {
SharedInfo* sharedInfo = NULL;
try {
+ // TODO: We could allocate the IOBuf object and SharedInfo all in a single
+ // memory allocation. We could use the existing HeapStorage class, and
+ // define a new kSharedInfoInUse flag. We could change our code to call
+ // releaseStorage(kFlagFreeSharedInfo) when this kFlagFreeSharedInfo,
+ // rather than directly calling delete.
sharedInfo = new SharedInfo(freeFn, userData);
uint8_t* bufPtr = static_cast<uint8_t*>(buf);
NULL));
}
-IOBuf::IOBuf(uint8_t* end)
- : next_(this),
- prev_(this),
- data_(int_.buf),
- length_(0),
- flags_(0) {
- assert(end - int_.buf == kMaxInternalDataSize);
- assert(end - reinterpret_cast<uint8_t*>(this) == kMaxIOBufSize);
-}
-
IOBuf::IOBuf(ExtBufTypeEnum type,
uint32_t flags,
uint8_t* buf,
: next_(this),
prev_(this),
data_(data),
+ buf_(buf),
length_(length),
- flags_(kFlagExt | flags) {
- ext_.capacity = capacity;
- ext_.type = type;
- ext_.buf = buf;
- ext_.sharedInfo = sharedInfo;
-
+ capacity_(capacity),
+ flags_(flags),
+ type_(type),
+ sharedInfo_(sharedInfo) {
assert(data >= buf);
assert(data + length <= buf + capacity);
assert(static_cast<bool>(flags & kFlagUserOwned) ==
(void)next_->unlink();
}
- if (flags_ & kFlagExt) {
- decrementRefcount();
- }
+ decrementRefcount();
}
bool IOBuf::empty() const {
}
unique_ptr<IOBuf> IOBuf::cloneOne() const {
- if (flags_ & kFlagExt) {
- if (ext_.sharedInfo) {
- flags_ |= kFlagMaybeShared;
- }
- unique_ptr<IOBuf> iobuf(new IOBuf(static_cast<ExtBufTypeEnum>(ext_.type),
- flags_, ext_.buf, ext_.capacity,
- data_, length_,
- ext_.sharedInfo));
- if (ext_.sharedInfo) {
- ext_.sharedInfo->refcount.fetch_add(1, std::memory_order_acq_rel);
- }
- return iobuf;
- } else {
- // We have an internal data buffer that cannot be shared
- // Allocate a new IOBuf and copy the data into it.
- unique_ptr<IOBuf> iobuf(IOBuf::create(kMaxInternalDataSize));
- assert((iobuf->flags_ & kFlagExt) == 0);
- iobuf->data_ += headroom();
- memcpy(iobuf->data_, data_, length_);
- iobuf->length_ = length_;
- return iobuf;
+ if (sharedInfo_) {
+ flags_ |= kFlagMaybeShared;
}
+ unique_ptr<IOBuf> iobuf(new IOBuf(static_cast<ExtBufTypeEnum>(type_),
+ flags_, buf_, capacity_,
+ data_, length_,
+ sharedInfo_));
+ if (sharedInfo_) {
+ sharedInfo_->refcount.fetch_add(1, std::memory_order_acq_rel);
+ }
+ return iobuf;
}
void IOBuf::unshareOneSlow() {
- // Internal buffers are always unshared, so unshareOneSlow() can only be
- // called for external buffers
- assert(flags_ & kFlagExt);
-
// Allocate a new buffer for the data
uint8_t* buf;
SharedInfo* sharedInfo;
uint32_t actualCapacity;
- allocExtBuffer(ext_.capacity, &buf, &sharedInfo, &actualCapacity);
+ allocExtBuffer(capacity_, &buf, &sharedInfo, &actualCapacity);
// Copy the data
// Maintain the same amount of headroom. Since we maintained the same
// Release our reference on the old buffer
decrementRefcount();
- // Make sure kFlagExt is set, and kFlagUserOwned and kFlagFreeSharedInfo
- // are not set.
- flags_ = kFlagExt;
+ // Make sure kFlagUserOwned, kFlagMaybeShared, and kFlagFreeSharedInfo
+ // are all cleared.
+ flags_ = 0;
// Update the buffer pointers to point to the new buffer
data_ = buf + headlen;
- ext_.buf = buf;
- ext_.sharedInfo = sharedInfo;
+ buf_ = buf;
+ sharedInfo_ = sharedInfo;
}
void IOBuf::unshareChained() {
assert(remaining == 0);
// Point at the new buffer
- if (flags_ & kFlagExt) {
- decrementRefcount();
- }
+ decrementRefcount();
- // Make sure kFlagExt is set, and kFlagUserOwned and kFlagFreeSharedInfo
- // are not set.
- flags_ = kFlagExt;
+ // Make sure kFlagUserOwned, kFlagMaybeShared, and kFlagFreeSharedInfo
+ // are all cleared.
+ flags_ = 0;
- ext_.capacity = actualCapacity;
- ext_.type = kExtAllocated;
- ext_.buf = newBuf;
- ext_.sharedInfo = newInfo;
+ capacity_ = actualCapacity;
+ type_ = kExtAllocated;
+ buf_ = newBuf;
+ sharedInfo_ = newInfo;
data_ = newData;
length_ = newLength;
}
void IOBuf::decrementRefcount() {
- assert(flags_ & kFlagExt);
-
// Externally owned buffers don't have a SharedInfo object and aren't managed
// by the reference count
if (flags_ & kFlagUserOwned) {
- assert(ext_.sharedInfo == NULL);
+ assert(sharedInfo_ == nullptr);
return;
}
// Decrement the refcount
- uint32_t newcnt = ext_.sharedInfo->refcount.fetch_sub(
+ uint32_t newcnt = sharedInfo_->refcount.fetch_sub(
1, std::memory_order_acq_rel);
// Note that fetch_sub() returns the value before we decremented.
// If it is 1, we were the only remaining user; if it is greater there are
// SharedInfo object.) However, handling this specially with a flag seems
// like it shouldn't be problematic.
if (flags_ & kFlagFreeSharedInfo) {
- delete ext_.sharedInfo;
+ delete sharedInfo_;
}
}
// If we have a buffer allocated with malloc and we just need more tailroom,
// try to use realloc()/rallocm() to grow the buffer in place.
- if ((flags_ & (kFlagExt | kFlagUserOwned)) == kFlagExt &&
- (ext_.sharedInfo->freeFn == nullptr) &&
+ if ((flags_ & kFlagUserOwned) == 0 && (sharedInfo_->freeFn == nullptr) &&
length_ != 0 && oldHeadroom >= minHeadroom) {
if (usingJEMalloc()) {
size_t headSlack = oldHeadroom - minHeadroom;
// much" headroom to be 25% of the capacity.
if (headSlack * 4 <= newCapacity) {
size_t allocatedCapacity = capacity() + sizeof(SharedInfo);
- void* p = ext_.buf;
+ void* p = buf_;
if (allocatedCapacity >= jemallocMinInPlaceExpandable) {
int r = rallocm(&p, &newAllocatedCapacity, newAllocatedCapacity,
0, ALLOCM_NO_MOVE);
} else { // Not using jemalloc
size_t copySlack = capacity() - length_;
if (copySlack * 2 <= length_) {
- void* p = realloc(ext_.buf, newAllocatedCapacity);
+ void* p = realloc(buf_, newAllocatedCapacity);
if (UNLIKELY(p == nullptr)) {
throw std::bad_alloc();
}
}
newBuffer = static_cast<uint8_t*>(p);
memcpy(newBuffer + minHeadroom, data_, length_);
- if ((flags_ & (kFlagExt | kFlagUserOwned)) == kFlagExt) {
+ if ((flags_ & kFlagUserOwned) == 0) {
freeExtBuffer();
}
newHeadroom = minHeadroom;
initExtBuffer(newBuffer, newAllocatedCapacity, &info, &cap);
if (flags_ & kFlagFreeSharedInfo) {
- delete ext_.sharedInfo;
+ delete sharedInfo_;
}
- flags_ = kFlagExt;
- ext_.capacity = cap;
- ext_.type = kExtAllocated;
- ext_.buf = newBuffer;
- ext_.sharedInfo = info;
+ flags_ = 0;
+ capacity_ = cap;
+ type_ = kExtAllocated;
+ buf_ = newBuffer;
+ sharedInfo_ = info;
data_ = newBuffer + newHeadroom;
// length_ is unchanged
}
void IOBuf::freeExtBuffer() {
- DCHECK((flags_ & (kFlagExt | kFlagUserOwned)) == kFlagExt);
+ DCHECK((flags_ & kFlagUserOwned) == 0);
- if (ext_.sharedInfo->freeFn) {
+ if (sharedInfo_->freeFn) {
try {
- ext_.sharedInfo->freeFn(ext_.buf, ext_.sharedInfo->userData);
+ sharedInfo_->freeFn(buf_, sharedInfo_->userData);
} catch (...) {
// The user's free function should never throw. Otherwise we might
// throw from the IOBuf destructor. Other code paths like coalesce()
abort();
}
} else {
- free(ext_.buf);
+ free(buf_);
}
}
// Determine how much space we should allocate. We'll store the SharedInfo
// for the external buffer just after the buffer itself. (We store it just
// after the buffer rather than just before so that the code can still just
- // use free(ext_.buf) to free the buffer.)
+ // use free(buf_) to free the buffer.)
size_t minSize = static_cast<size_t>(minCapacity) + sizeof(SharedInfo);
// Add room for padding so that the SharedInfo will be aligned on an 8-byte
// boundary.
fbstring IOBuf::moveToFbString() {
// malloc-allocated buffers are just fine, everything else needs
// to be turned into one.
- if ((flags_ & (kFlagExt | kFlagUserOwned)) != kFlagExt || // not malloc()-ed
- ext_.sharedInfo->freeFn != nullptr || // not malloc()-ed
+ if ((flags_ & kFlagUserOwned) || // user owned, not ours to give up
+ sharedInfo_->freeFn != nullptr || // not malloc()-ed
headroom() != 0 || // malloc()-ed block doesn't start at beginning
tailroom() == 0 || // no room for NUL terminator
isShared() || // shared
AcquireMallocatedString());
if (flags_ & kFlagFreeSharedInfo) {
- delete ext_.sharedInfo;
+ delete sharedInfo_;
}
- // Reset to internal buffer.
- flags_ = 0;
+ // Reset to a state where we can be deleted cleanly
+ flags_ = kFlagUserOwned;
+ sharedInfo_ = nullptr;
+ buf_ = nullptr;
clear();
return str;
}
*/
static std::unique_ptr<IOBuf> create(uint32_t capacity);
+ /**
+ * Create a new IOBuf, using a single memory allocation to allocate space
+ * for both the IOBuf object and the data storage space.
+ *
+ * This saves one memory allocation. However, it can be wasteful if you
+ * later need to grow the buffer using reserve(). If the buffer needs to be
+ * reallocated, the space originally allocated will not be freed() until the
+ * IOBuf object itself is also freed. (It can also be slightly wasteful in
+ * some cases where you clone this IOBuf and then free the original IOBuf.)
+ */
+ static std::unique_ptr<IOBuf> createCombined(uint32_t capacity);
+
+ /**
+ * Create a new IOBuf, using separate memory allocations for the IOBuf object
+ * for the IOBuf and the data storage space.
+ *
+ * This requires two memory allocations, but saves space in the long run
+ * if you know that you will need to reallocate the data buffer later.
+ */
+ static std::unique_ptr<IOBuf> createSeparate(uint32_t capacity);
+
/**
* Allocate a new IOBuf chain with the requested total capacity, allocating
* no more than maxBufCapacity to each buffer.
* get a pointer to the start of the data within the buffer.
*/
const uint8_t* buffer() const {
- return (flags_ & kFlagExt) ? ext_.buf : int_.buf;
+ return buf_;
}
/**
* actually safe to write to the buffer.
*/
uint8_t* writableBuffer() {
- return (flags_ & kFlagExt) ? ext_.buf : int_.buf;
+ return buf_;
}
/**
* get a pointer to the end of the data within the buffer.
*/
const uint8_t* bufferEnd() const {
- return (flags_ & kFlagExt) ?
- ext_.buf + ext_.capacity :
- int_.buf + kMaxInternalDataSize;
+ return buf_ + capacity_;
}
/**
* method to get the length of the actual valid data in this IOBuf.
*/
uint32_t capacity() const {
- return (flags_ & kFlagExt) ? ext_.capacity : kMaxInternalDataSize;
+ return capacity_;
}
/**
return true;
}
- // an internal buffer wouldn't have kFlagMaybeShared or kFlagUserOwned
- // so we would have returned false already. The only remaining case
- // is an external buffer which may be shared, so we need to read
- // the reference count.
- assert((flags_ & (kFlagExt | kFlagMaybeShared)) ==
- (kFlagExt | kFlagMaybeShared));
-
- bool shared =
- ext_.sharedInfo->refcount.load(std::memory_order_acquire) > 1;
+ // kFlagMaybeShared is set, so we need to check the reference count.
+ // (Checking the reference count requires an atomic operation, which is why
+ // we prefer to only check kFlagMaybeShared if possible.)
+ DCHECK(flags_ & kFlagMaybeShared);
+ bool shared = sharedInfo_->refcount.load(std::memory_order_acquire) > 1;
if (!shared) {
// we're the last one left
flags_ &= ~kFlagMaybeShared;
*/
folly::fbvector<struct iovec> getIov() const;
- // Overridden operator new and delete.
- // These directly use malloc() and free() to allocate the space for IOBuf
- // objects. This is needed since IOBuf::create() manually uses malloc when
- // allocating IOBuf objects with an internal buffer.
+ /*
+ * Overridden operator new and delete.
+ * These perform specialized memory management to help support
+ * createCombined(), which allocates IOBuf objects together with the buffer
+ * data.
+ */
void* operator new(size_t size);
void* operator new(size_t size, void* ptr);
void operator delete(void* ptr);
private:
enum FlagsEnum : uint32_t {
- kFlagExt = 0x1,
- kFlagUserOwned = 0x2,
- kFlagFreeSharedInfo = 0x4,
- kFlagMaybeShared = 0x8,
+ kFlagUserOwned = 0x1,
+ kFlagFreeSharedInfo = 0x2,
+ kFlagMaybeShared = 0x4,
};
- // Values for the ExternalBuf type field.
+ // Values for the type_ field.
// We currently don't really use this for anything, other than to have it
// around for debugging purposes. We store it at the moment just because we
- // have the 4 extra bytes in the ExternalBuf struct that would just be
- // padding otherwise.
+ // have the 4 extra bytes that would just be padding otherwise.
enum ExtBufTypeEnum {
kExtAllocated = 0,
kExtUserSupplied = 1,
kExtUserOwned = 2,
+ kCombinedAlloc = 3,
};
struct SharedInfo {
void* userData;
std::atomic<uint32_t> refcount;
};
- struct ExternalBuf {
- uint32_t capacity;
- uint32_t type;
- uint8_t* buf;
- // SharedInfo may be NULL if kFlagUserOwned is set. It is non-NULL
- // in all other cases.
- SharedInfo* sharedInfo;
- };
- struct InternalBuf {
- uint8_t buf[] __attribute__((aligned));
- };
-
- // The maximum size for an IOBuf object, including any internal data buffer
- static const uint32_t kMaxIOBufSize = 256;
- static const uint32_t kMaxInternalDataSize;
+ // Helper structs for use by operator new and delete
+ struct HeapPrefix;
+ struct HeapStorage;
+ struct HeapFullStorage;
// Forbidden copy constructor and assignment opererator
IOBuf(IOBuf const &);
IOBuf& operator=(IOBuf const &);
- /**
- * Create a new IOBuf with internal data.
- *
- * end is a pointer to the end of the IOBuf's internal data buffer.
- */
- explicit IOBuf(uint8_t* end);
-
/**
* Create a new IOBuf pointing to an external buffer.
*
uint8_t** bufReturn,
SharedInfo** infoReturn,
uint32_t* capacityReturn);
+ static void releaseStorage(HeapStorage* storage, uint16_t freeFlags);
+ static void freeInternalBuf(void* buf, void* userData);
/*
* Member variables
* This may refer to any subsection of the actual buffer capacity.
*/
uint8_t* data_;
+ uint8_t* buf_;
uint32_t length_;
+ uint32_t capacity_;
mutable uint32_t flags_;
-
- union {
- ExternalBuf ext_;
- InternalBuf int_;
- };
+ uint32_t type_;
+ // SharedInfo may be NULL if kFlagUserOwned is set. It is non-NULL
+ // in all other cases.
+ SharedInfo* sharedInfo_;
struct DeleterBase {
virtual ~DeleterBase() { }
projects / folly.git / commitdiff