81 lines
3.5 KiB
C
81 lines
3.5 KiB
C
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//=- CachePruning.h - Helper to manage the pruning of a cache dir -*- C++ -*-=//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements pruning of a directory intended for cache storage, using
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// various policies.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_SUPPORT_CACHE_PRUNING_H
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#define LLVM_SUPPORT_CACHE_PRUNING_H
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#include "llvm/ADT/Optional.h"
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#include <chrono>
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namespace llvm {
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template <typename T> class Expected;
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class StringRef;
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/// Policy for the pruneCache() function. A default constructed
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/// CachePruningPolicy provides a reasonable default policy.
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struct CachePruningPolicy {
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/// The pruning interval. This is intended to be used to avoid scanning the
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/// directory too often. It does not impact the decision of which file to
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/// prune. A value of 0 forces the scan to occur. A value of None disables
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/// pruning.
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llvm::Optional<std::chrono::seconds> Interval = std::chrono::seconds(1200);
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/// The expiration for a file. When a file hasn't been accessed for Expiration
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/// seconds, it is removed from the cache. A value of 0 disables the
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/// expiration-based pruning.
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std::chrono::seconds Expiration = std::chrono::hours(7 * 24); // 1w
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/// The maximum size for the cache directory, in terms of percentage of the
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/// available space on the disk. Set to 100 to indicate no limit, 50 to
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/// indicate that the cache size will not be left over half the available disk
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/// space. A value over 100 will be reduced to 100. A value of 0 disables the
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/// percentage size-based pruning.
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unsigned MaxSizePercentageOfAvailableSpace = 75;
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/// The maximum size for the cache directory in bytes. A value over the amount
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/// of available space on the disk will be reduced to the amount of available
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/// space. A value of 0 disables the absolute size-based pruning.
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uint64_t MaxSizeBytes = 0;
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/// The maximum number of files in the cache directory. A value of 0 disables
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/// the number of files based pruning.
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///
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/// This defaults to 1000000 because with that many files there are
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/// diminishing returns on the effectiveness of the cache. Some systems have a
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/// limit on total number of files, and some also limit the number of files
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/// per directory, such as Linux ext4, with the default setting (block size is
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/// 4096 and large_dir disabled), there is a per-directory entry limit of
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/// 508*510*floor(4096/(40+8))~=20M for average filename length of 40.
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uint64_t MaxSizeFiles = 1000000;
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};
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/// Parse the given string as a cache pruning policy. Defaults are taken from a
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/// default constructed CachePruningPolicy object.
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/// For example: "prune_interval=30s:prune_after=24h:cache_size=50%"
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/// which means a pruning interval of 30 seconds, expiration time of 24 hours
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/// and maximum cache size of 50% of available disk space.
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Expected<CachePruningPolicy> parseCachePruningPolicy(StringRef PolicyStr);
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/// Peform pruning using the supplied policy, returns true if pruning
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/// occurred, i.e. if Policy.Interval was expired.
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///
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/// As a safeguard against data loss if the user specifies the wrong directory
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/// as their cache directory, this function will ignore files not matching the
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/// pattern "llvmcache-*".
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bool pruneCache(StringRef Path, CachePruningPolicy Policy);
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} // namespace llvm
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#endif
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