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#pragma once
#include "../core/slang-crypto.h"
#include "../core/slang-io.h"
#include "../core/slang-string.h"
#include "slang.h"
#include <mutex>
namespace Slang
{
/// Implements a simple persistent cache on the filesystem for storing key/value pairs.
/// Keys are SHA1 hashes and values are arbitrary blobs of data.
/// The cache is save for concurrent access from multiple threads/processes by using
/// a lock file within the cache directory. Furthermore, the cache implements a LRU
/// eviction policy.
class PersistentCache : public RefObject
{
public:
struct Desc
{
// The root directory for the cache.
const char* directory = nullptr;
// The maximum number of entries stored in the cache. By default, there is no limit.
Count maxEntryCount = 0;
};
struct Stats
{
// Number of cache hits since last resetting the stats.
Count hitCount;
// Number of cache misses since last resetting the stats.
Count missCount;
// Current number of entries in the cache.
Count entryCount;
};
using Key = SHA1::Digest;
PersistentCache(const Desc& desc);
~PersistentCache();
/// Clear the contents of the cache by removing the cache index and all entry files.
SlangResult clear();
const Stats& getStats() const { return m_stats; }
void resetStats();
/// Read an entry from the cache.
/// Returns SLANG_OK if successful, SLANG_E_NOT_FOUND if the entry is not in the cache.
SlangResult readEntry(const Key& key, ISlangBlob** outData);
/// Write an entry to the cache.
/// Returns SLANG_OK if successful.
SlangResult writeEntry(const Key& key, ISlangBlob* data);
private:
struct CacheEntry
{
Key key;
uint32_t age;
};
using CacheIndex = List<CacheEntry>;
SlangResult initialize();
String getEntryFileName(const Key& key);
SlangResult readIndex(const String& fileName, CacheIndex& outIndex);
SlangResult writeIndex(const String& fileName, const CacheIndex& index);
String m_cacheDirectory;
String m_lockFileName;
String m_indexFileName;
// For exclusive locking we need both a mutex (acquired first)
// followed by a a file lock. The mutex is needed because on Linux
// the file lock is only locking between processes, not threads.
std::mutex m_mutex;
Slang::LockFile m_lockFile;
Count m_maxEntryCount;
Stats m_stats;
// Used for unit tests.
friend struct PersistentCacheTest;
};
} // namespace Slang
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