clang 17.0.0git
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1//===- DirectoryWatcher.h - Listens for directory file changes --*- C++ -*-===//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
12#include "llvm/ADT/ArrayRef.h"
13#include "llvm/ADT/StringRef.h"
14#include "llvm/Support/Error.h"
15#include <functional>
16#include <memory>
17#include <string>
19namespace clang {
20/// Provides notifications for file changes in a directory.
22/// Invokes client-provided function on every filesystem event in the watched
23/// directory. Initially the watched directory is scanned and for every file
24/// found, an event is synthesized as if the file was added.
26/// This is not a general purpose directory monitoring tool - list of
27/// limitations follows.
29/// Only flat directories with no subdirectories are supported. In case
30/// subdirectories are present the behavior is unspecified - events *might* be
31/// passed to Receiver on macOS (due to FSEvents being used) while they
32/// *probably* won't be passed on Linux (due to inotify being used).
34/// Known potential inconsistencies
35/// - For files that are deleted befor the initial scan processed them, clients
36/// might receive Removed notification without any prior Added notification.
37/// - Multiple notifications might be produced when a file is added to the
38/// watched directory during the initial scan. We are choosing the lesser evil
39/// here as the only known alternative strategy would be to invalidate the
40/// watcher instance and force user to create a new one whenever filesystem
41/// event occurs during the initial scan but that would introduce continuous
42/// restarting failure mode (watched directory is not always "owned" by the same
43/// process that is consuming it). Since existing clients can handle duplicate
44/// events well, we decided for simplicity.
46/// Notifications are provided only for changes done through local user-space
47/// filesystem interface. Specifically, it's unspecified if notification would
48/// be provided in case of a:
49/// - a file mmap-ed and changed
50/// - a file changed via remote (NFS) or virtual (/proc) FS access to monitored
51/// directory
52/// - another filesystem mounted to the watched directory
54/// No support for LLVM VFS.
56/// It is unspecified whether notifications for files being deleted are sent in
57/// case the whole watched directory is sent.
59/// Directories containing "too many" files and/or receiving events "too
60/// frequently" are not supported - if the initial scan can't be finished before
61/// the watcher instance gets invalidated (see WatcherGotInvalidated) there's no
62/// good error handling strategy - the only option for client is to destroy the
63/// watcher, restart watching with new instance and hope it won't repeat.
66 struct Event {
67 enum class EventKind {
68 Removed,
69 /// Content of a file was modified.
71 /// The watched directory got deleted.
73 /// The DirectoryWatcher that originated this event is no longer valid and
74 /// its behavior is unspecified.
75 ///
76 /// The prime case is kernel signalling to OS-specific implementation of
77 /// DirectoryWatcher some resource limit being hit.
78 /// *Usually* kernel starts dropping or squashing events together after
79 /// that and so would DirectoryWatcher. This means that *some* events
80 /// might still be passed to Receiver but this behavior is unspecified.
81 ///
82 /// Another case is after the watched directory itself is deleted.
83 /// WatcherGotInvalidated will be received at least once during
84 /// DirectoryWatcher instance lifetime - when handling errors this is done
85 /// on best effort basis, when an instance is being destroyed then this is
86 /// guaranteed.
87 ///
88 /// The only proper response to this kind of event is to destruct the
89 /// originating DirectoryWatcher instance and create a new one.
91 };
94 /// Filename that this event is related to or an empty string in
95 /// case this event is related to the watched directory itself.
96 std::string Filename;
98 Event(EventKind Kind, llvm::StringRef Filename)
100 };
102 /// llvm fatal_error if \param Path doesn't exist or isn't a directory.
103 /// Returns llvm::Expected Error if OS kernel API told us we can't start
104 /// watching. In such case it's unclear whether just retrying has any chance
105 /// to succeed.
107 create(llvm::StringRef Path,
108 std::function<void(llvm::ArrayRef<DirectoryWatcher::Event> Events,
109 bool IsInitial)>
110 Receiver,
111 bool WaitForInitialSync);
113 virtual ~DirectoryWatcher() = default;
119 DirectoryWatcher() = default;
122} // namespace clang
Provides notifications for file changes in a directory.
DirectoryWatcher(DirectoryWatcher &&)=default
virtual ~DirectoryWatcher()=default
static llvm::Expected< std::unique_ptr< DirectoryWatcher > > create(llvm::StringRef Path, std::function< void(llvm::ArrayRef< DirectoryWatcher::Event > Events, bool IsInitial)> Receiver, bool WaitForInitialSync)
llvm fatal_error if
DirectoryWatcher(const DirectoryWatcher &)=delete
DirectoryWatcher & operator=(const DirectoryWatcher &)=delete
Event(EventKind Kind, llvm::StringRef Filename)
@ WatcherGotInvalidated
The DirectoryWatcher that originated this event is no longer valid and its behavior is unspecified.
@ WatchedDirRemoved
The watched directory got deleted.
@ Modified
Content of a file was modified.
std::string Filename
Filename that this event is related to or an empty string in case this event is related to the watche...