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+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+//
+// This file contains the specification, but not the implementations,
+// of the types/operations/etc. that should be defined by a platform
+// specific port_<platform>.h file. Use this file as a reference for
+// how to port this package to a new platform.
+
+#ifndef STORAGE_LEVELDB_PORT_PORT_EXAMPLE_H_
+#define STORAGE_LEVELDB_PORT_PORT_EXAMPLE_H_
+
+namespace leveldb {
+namespace port {
+
+// TODO(jorlow): Many of these belong more in the environment class rather than
+// here. We should try moving them and see if it affects perf.
+
+// The following boolean constant must be true on a little-endian machine
+// and false otherwise.
+static const bool kLittleEndian = true /* or some other expression */;
+
+// ------------------ Threading -------------------
+
+// A Mutex represents an exclusive lock.
+class Mutex {
+ public:
+ Mutex();
+ ~Mutex();
+
+ // Lock the mutex. Waits until other lockers have exited.
+ // Will deadlock if the mutex is already locked by this thread.
+ void Lock();
+
+ // Unlock the mutex.
+ // REQUIRES: This mutex was locked by this thread.
+ void Unlock();
+
+ // Optionally crash if this thread does not hold this mutex.
+ // The implementation must be fast, especially if NDEBUG is
+ // defined. The implementation is allowed to skip all checks.
+ void AssertHeld();
+};
+
+class CondVar {
+ public:
+ explicit CondVar(Mutex* mu);
+ ~CondVar();
+
+ // Atomically release *mu and block on this condition variable until
+ // either a call to SignalAll(), or a call to Signal() that picks
+ // this thread to wakeup.
+ // REQUIRES: this thread holds *mu
+ void Wait();
+
+ // If there are some threads waiting, wake up at least one of them.
+ void Signal();
+
+ // Wake up all waiting threads.
+ void SignallAll();
+};
+
+// Thread-safe initialization.
+// Used as follows:
+// static port::OnceType init_control = LEVELDB_ONCE_INIT;
+// static void Initializer() { ... do something ...; }
+// ...
+// port::InitOnce(&init_control, &Initializer);
+typedef intptr_t OnceType;
+#define LEVELDB_ONCE_INIT 0
+extern void InitOnce(port::OnceType*, void (*initializer)());
+
+// A type that holds a pointer that can be read or written atomically
+// (i.e., without word-tearing.)
+class AtomicPointer {
+ private:
+ intptr_t rep_;
+ public:
+ // Initialize to arbitrary value
+ AtomicPointer();
+
+ // Initialize to hold v
+ explicit AtomicPointer(void* v) : rep_(v) { }
+
+ // Read and return the stored pointer with the guarantee that no
+ // later memory access (read or write) by this thread can be
+ // reordered ahead of this read.
+ void* Acquire_Load() const;
+
+ // Set v as the stored pointer with the guarantee that no earlier
+ // memory access (read or write) by this thread can be reordered
+ // after this store.
+ void Release_Store(void* v);
+
+ // Read the stored pointer with no ordering guarantees.
+ void* NoBarrier_Load() const;
+
+ // Set va as the stored pointer with no ordering guarantees.
+ void NoBarrier_Store(void* v);
+};
+
+// ------------------ Compression -------------------
+
+// Store the snappy compression of "input[0,input_length-1]" in *output.
+// Returns false if snappy is not supported by this port.
+extern bool Snappy_Compress(const char* input, size_t input_length,
+ std::string* output);
+
+// If input[0,input_length-1] looks like a valid snappy compressed
+// buffer, store the size of the uncompressed data in *result and
+// return true. Else return false.
+extern bool Snappy_GetUncompressedLength(const char* input, size_t length,
+ size_t* result);
+
+// Attempt to snappy uncompress input[0,input_length-1] into *output.
+// Returns true if successful, false if the input is invalid lightweight
+// compressed data.
+//
+// REQUIRES: at least the first "n" bytes of output[] must be writable
+// where "n" is the result of a successful call to
+// Snappy_GetUncompressedLength.
+extern bool Snappy_Uncompress(const char* input_data, size_t input_length,
+ char* output);
+
+// ------------------ Miscellaneous -------------------
+
+// If heap profiling is not supported, returns false.
+// Else repeatedly calls (*func)(arg, data, n) and then returns true.
+// The concatenation of all "data[0,n-1]" fragments is the heap profile.
+extern bool GetHeapProfile(void (*func)(void*, const char*, int), void* arg);
+
+} // namespace port
+} // namespace leveldb
+
+#endif // STORAGE_LEVELDB_PORT_PORT_EXAMPLE_H_