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141 lines
4.8 KiB
141 lines
4.8 KiB
// 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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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 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();
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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();
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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();
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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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// Thread-safe initialization.
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// Used as follows:
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// static port::OnceType init_control = LEVELDB_ONCE_INIT;
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// static void Initializer() { ... do something ...; }
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// ...
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// port::InitOnce(&init_control, &Initializer);
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typedef intptr_t OnceType;
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#define LEVELDB_ONCE_INIT 0
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extern void InitOnce(port::OnceType*, void (*initializer)());
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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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extern 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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extern 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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extern 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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extern 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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