05709fb43e
This is not an API-breaking change, because it reduces the API that the leveldb embedder must implement. The project will build just fine against ports that still implement InitOnce. C++11 guarantees thread-safe initialization of static variables inside functions. This is a more restricted form of std::call_once or pthread_once_t (e.g., single call site), so the compiler might be able to generate better code [1]. Equally important, having less code in port_example.h makes it easier to port to other platforms. Due to the change above, this CL introduces a new approach for storing the singleton BytewiseComparatorImpl instance returned by BytewiseComparator(). The new approach avoids a dynamic memory allocation, which eliminates the false positive from LeakSanitizer reported in https://github.com/google/leveldb/issues/200 [1] https://stackoverflow.com/a/27206650/ ------------- Created by MOE: https://github.com/google/moe MOE_MIGRATED_REVID=212348004
134 lines
4.5 KiB
C++
134 lines
4.5 KiB
C++
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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//
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// This file contains the specification, but not the implementations,
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// of the types/operations/etc. that should be defined by a platform
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// specific port_<platform>.h file. Use this file as a reference for
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// how to port this package to a new platform.
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#ifndef STORAGE_LEVELDB_PORT_PORT_EXAMPLE_H_
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#define STORAGE_LEVELDB_PORT_PORT_EXAMPLE_H_
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#include "port/thread_annotations.h"
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namespace leveldb {
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namespace port {
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// TODO(jorlow): Many of these belong more in the environment class rather than
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// here. We should try moving them and see if it affects perf.
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// The following boolean constant must be true on a little-endian machine
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// and false otherwise.
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static const bool kLittleEndian = true /* or some other expression */;
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// ------------------ Threading -------------------
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// A Mutex represents an exclusive lock.
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class LOCKABLE Mutex {
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public:
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Mutex();
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~Mutex();
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// Lock the mutex. Waits until other lockers have exited.
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// Will deadlock if the mutex is already locked by this thread.
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void Lock() EXCLUSIVE_LOCK_FUNCTION();
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// Unlock the mutex.
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// REQUIRES: This mutex was locked by this thread.
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void Unlock() UNLOCK_FUNCTION();
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// Optionally crash if this thread does not hold this mutex.
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// The implementation must be fast, especially if NDEBUG is
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// defined. The implementation is allowed to skip all checks.
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void AssertHeld() ASSERT_EXCLUSIVE_LOCK();
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};
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class CondVar {
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public:
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explicit CondVar(Mutex* mu);
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~CondVar();
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// Atomically release *mu and block on this condition variable until
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// either a call to SignalAll(), or a call to Signal() that picks
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// this thread to wakeup.
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// REQUIRES: this thread holds *mu
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void Wait();
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// If there are some threads waiting, wake up at least one of them.
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void Signal();
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// Wake up all waiting threads.
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void SignallAll();
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};
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// A type that holds a pointer that can be read or written atomically
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// (i.e., without word-tearing.)
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class AtomicPointer {
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private:
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intptr_t rep_;
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public:
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// Initialize to arbitrary value
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AtomicPointer();
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// Initialize to hold v
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explicit AtomicPointer(void* v) : rep_(v) { }
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// Read and return the stored pointer with the guarantee that no
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// later memory access (read or write) by this thread can be
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// reordered ahead of this read.
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void* Acquire_Load() const;
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// Set v as the stored pointer with the guarantee that no earlier
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// memory access (read or write) by this thread can be reordered
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// after this store.
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void Release_Store(void* v);
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// Read the stored pointer with no ordering guarantees.
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void* NoBarrier_Load() const;
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// Set va as the stored pointer with no ordering guarantees.
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void NoBarrier_Store(void* v);
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};
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// ------------------ Compression -------------------
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// Store the snappy compression of "input[0,input_length-1]" in *output.
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// Returns false if snappy is not supported by this port.
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bool Snappy_Compress(const char* input, size_t input_length,
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std::string* output);
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// If input[0,input_length-1] looks like a valid snappy compressed
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// buffer, store the size of the uncompressed data in *result and
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// return true. Else return false.
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bool Snappy_GetUncompressedLength(const char* input, size_t length,
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size_t* result);
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// Attempt to snappy uncompress input[0,input_length-1] into *output.
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// Returns true if successful, false if the input is invalid lightweight
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// compressed data.
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//
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// REQUIRES: at least the first "n" bytes of output[] must be writable
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// where "n" is the result of a successful call to
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// Snappy_GetUncompressedLength.
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bool Snappy_Uncompress(const char* input_data, size_t input_length,
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char* output);
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// ------------------ Miscellaneous -------------------
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// If heap profiling is not supported, returns false.
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// Else repeatedly calls (*func)(arg, data, n) and then returns true.
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// The concatenation of all "data[0,n-1]" fragments is the heap profile.
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bool GetHeapProfile(void (*func)(void*, const char*, int), void* arg);
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// Extend the CRC to include the first n bytes of buf.
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//
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// Returns zero if the CRC cannot be extended using acceleration, else returns
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// the newly extended CRC value (which may also be zero).
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uint32_t AcceleratedCRC32C(uint32_t crc, const char* buf, size_t size);
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} // namespace port
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} // namespace leveldb
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#endif // STORAGE_LEVELDB_PORT_PORT_EXAMPLE_H_
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