FileSystemWatcher Class

class Utils::FileSystemWatcher

The FileSystemWatcher class is a file watcher that internally uses a centralized QFileSystemWatcher and enforces limits on Mac OS. More...

Header: #include <FileSystemWatcher>
Inherits: QObject

Public Functions

FileSystemWatcher(QObject *parent = nullptr)
FileSystemWatcher(int id, QObject *parent = nullptr)

Detailed Description

Design Considerations

Constructing/Destructing a QFileSystemWatcher is expensive. This can be worked around by using a centralized watcher.

Note: It is (still) possible to create several instances of a QFileSystemWatcher by passing an (arbitrary) integer id != 0 to the constructor. This allows separating watchers that easily exceed operating system limits from others (see below).

Mac OS Specifics

There is a hard limit on the number of file handles that can be open at one point per process on Mac OS X (e.g. it is 2560 on Mac OS X Snow Leopard Server, as shown by ulimit -a). Opening one or several .qmlproject's with a large number of directories to watch easily exceeds this. The results are crashes later on, e.g. when threads cannot be created any more.

This class implements a heuristic that the file system watcher used for .qmlproject files never uses more than half the number of available file handles. It also increases the number from rlim_cur to rlim_max - the old code in main.cpp failed, see last section in

for details.

Member Function Documentation

[explicit] FileSystemWatcher::FileSystemWatcher(QObject *parent = nullptr)

Creates a file system watcher with the ID 0 and the owner parent.

[explicit] FileSystemWatcher::FileSystemWatcher(int id, QObject *parent = nullptr)

Creates a file system watcher with the ID id and the owner parent.

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