blob: d47ab038d306750502306e794f2a397eff34e154 [file] [log] [blame]
// Copyright 2017 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include <stdint.h>
#include <algorithm>
#include <list>
#include <memory>
#include <unordered_map>
#include <vector>
#include "base/files/file.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/synchronization/lock.h"
#include "net/base/net_export.h"
#include "net/disk_cache/simple/simple_entry_format.h"
namespace disk_cache {
class SimpleSynchronousEntry;
// This keeps track of all the files SimpleCache has open, across all the
// backend instancess, in order to prevent us from running out of file
// descriptors.
// TODO(morlovich): Actually implement closing and re-opening of things if we
// run out.
// This class is thread-safe.
class NET_EXPORT_PRIVATE SimpleFileTracker {
enum class SubFile { FILE_0, FILE_1, FILE_SPARSE };
// A RAII helper that guards access to a file grabbed for use from
// SimpleFileTracker::Acquire(). While it's still alive, if IsOK() is true,
// then using the underlying base::File via get() or the -> operator will be
// safe.
// This class is movable but not copyable. It should only be used from a
// single logical sequence of execution, and should not outlive the
// corresponding SimpleSynchronousEntry.
class NET_EXPORT_PRIVATE FileHandle {
FileHandle(FileHandle&& other);
FileHandle& operator=(FileHandle&& other);
base::File* operator->() const;
base::File* get() const;
// Returns true if this handle points to a valid file. This should normally
// be the first thing called on the object, after getting it from
// SimpleFileTracker::Acquire.
bool IsOK() const;
friend class SimpleFileTracker;
FileHandle(SimpleFileTracker* file_tracker,
const SimpleSynchronousEntry* entry,
SimpleFileTracker::SubFile subfile,
base::File* file);
// All the pointer fields are nullptr in the default/moved away from form.
SimpleFileTracker* file_tracker_ = nullptr;
const SimpleSynchronousEntry* entry_ = nullptr;
SimpleFileTracker::SubFile subfile_;
base::File* file_ = nullptr;
struct EntryFileKey {
EntryFileKey() {}
explicit EntryFileKey(uint64_t hash) : entry_hash(hash) {}
uint64_t entry_hash = 0;
// 0 means this a non-doomed, active entry, for its backend that will be
// checked on OpenEntry(key) where hash(key) = entry_hash. Other values of
// |doom_generation| are used to generate distinct file names for entries
// that have been Doom()ed, either by explicit API call by the client or
// internal operation (eviction, collisions, etc.)
uint64_t doom_generation = 0;
// The default limit here is half of what's available on our target OS where
// Chrome has the lowest limit.
SimpleFileTracker(int file_limit = 512);
// Established |file| as what's backing |subfile| for |owner|. This is
// intended to be called when SimpleSynchronousEntry first sets up the file to
// transfer its ownership to SimpleFileTracker. Any Register() call must be
// eventually followed by a corresponding Close() call before the |owner| is
// destroyed. |file->IsValid()| must be true.
void Register(const SimpleSynchronousEntry* owner,
SubFile subfile,
std::unique_ptr<base::File> file);
// Lends out a file to SimpleSynchronousEntry for use. SimpleFileTracker
// will ensure that it doesn't close the file until the handle is destroyed.
// The caller should check .IsOK() on the returned value before using it, as
// it's possible that the file had to be closed and re-opened due to FD
// pressure, and that open may have failed. This should not be called twice
// with the exact same arguments until the handle returned from the previous
// such call is destroyed.
FileHandle Acquire(const SimpleSynchronousEntry* owner, SubFile subfile);
// Tells SimpleFileTracker that SimpleSynchronousEntry will not be interested
// in the file further, so it can be closed and forgotten about. It's OK to
// call this while a handle to the file is alive, in which case the effect
// takes place after the handle is destroyed.
// If Close() has been called and the handle to the file is no longer alive,
// a new backing file can be established by calling Register() again.
void Close(const SimpleSynchronousEntry* owner, SubFile file);
// Updates key->doom_generation to one not in use for the hash; it's the
// caller's responsibility to update file names accordingly, and to prevent
// others from stomping on things while this is going on. SimpleBackendImpl's
// entries_pending_doom_ is the mechanism for protecting this action from
// races.
void Doom(const SimpleSynchronousEntry* owner, EntryFileKey* key);
// Returns true if there is no in-memory state around, e.g. everything got
// cleaned up. This is a test-only method since this object is expected to be
// shared between multiple threads, in which case its return value may be
// outdated the moment it's returned.
bool IsEmptyForTesting();
struct TrackedFiles {
// We can potentially run through this state machine multiple times for
// FILE_1, as that's often missing, so SimpleSynchronousEntry can sometimes
// close and remove the file for an empty stream, then re-open it on actual
// data.
enum State {
// True if this isn't keeping track of anything any more.
bool Empty() const;
// True if this has open files. Note that this is not the same as !Empty()
// as this may be false when an entry had its files temporarily closed, but
// is still relevant.
bool HasOpenFiles() const;
// We use pointers to SimpleSynchronousEntry two ways:
// 1) As opaque keys. This is handy as it avoids having to compare paths in
// case multiple backends use the same key. Since we access the
// bookkeeping under |lock_|
// 2) To get info on the caller of our operation.
// Accessing |owner| from any other TrackedFiles would be unsafe (as it
// may be doing its own thing in a different thread).
const SimpleSynchronousEntry* owner;
EntryFileKey key;
// Some of these may be nullptr, if they are not open. Non-null pointers
// to files that are not valid will not be stored here.
// Note that these are stored indirect since we hand out pointers to these,
// and we don't want those to become invalid if some other thread appends
// things here.
std::unique_ptr<base::File> files[kSimpleEntryTotalFileCount];
State state[kSimpleEntryTotalFileCount];
std::list<TrackedFiles*>::iterator position_in_lru;
// true if position_in_lru is valid. For entries where we closed everything,
// we try not to keep them in the LRU so that we don't have to constantly
// rescan them.
bool in_lru;
// Marks the file that was previously returned by Acquire as eligible for
// closing again. Called by ~FileHandle.
void Release(const SimpleSynchronousEntry* owner, SubFile subfile);
// Precondition: entry for given |owner| must already be in tracked_files_
TrackedFiles* Find(const SimpleSynchronousEntry* owner);
// Handles state transition of closing file (when we are not deferring it),
// and moves the file out. Note that this may delete |*owners_files|.
std::unique_ptr<base::File> PrepareClose(TrackedFiles* owners_files,
int file_index);
// If too many files are open, picks some to close, and moves them to
// |*files_to_close|, updating other state as appropriate.
void CloseFilesIfTooManyOpen(
std::vector<std::unique_ptr<base::File>>* files_to_close);
// Tries to reopen given file, updating |*owners_files| if successful.
void ReopenFile(TrackedFiles* owners_files, SubFile subfile);
// Makes sure the entry is marked as most recently used, adding it to LRU
// if needed.
void EnsureInFrontOfLRU(TrackedFiles* owners_files);
base::Lock lock_;
std::unordered_map<uint64_t, std::vector<std::unique_ptr<TrackedFiles>>>
std::list<TrackedFiles*> lru_;
int file_limit_;
// How many actually open files we are using.
// Note that when a thread commits to closing a file, but hasn't actually
// executed the close yet, the file is no longer counted as open here, so this
// might be a little off. This should be OK as long as file_limit_ is set
// conservatively, considering SimpleCache's parallelism is bounded by a low
// number of threads, and getting it exact would require re-acquiring the
// lock after closing the file.
int open_files_ = 0;
} // namespace disk_cache