LogStorage Class

Detailed Description

LogStorage provides efficient log file management using memory-mapped files. Creates daily rotating log files in a configurable directory. Supports appending new entries, reading recent logs, clearing, and reloading.

The storage never changes the size of a file while it holds a view of that file. Windows refuses to truncate or shrink a file that any view or section maps (ERROR_USER_MAPPED_FILE), and two LogStorage instances can map the same day file at the same time. So:

• rotateLog() only grows a file, and only before it maps the file. If the grow fails, it maps the length the file already has.
• clearLogs() writes zeros over the mapped data. It does not truncate.
• When the file is full on the same day, appendLog() moves the newest lines to the start of the view and zeros the rest. It never writes past the view.

A day file is whole lines, then zeros up to maxSize. A reader of a day file uses readDayFileLines(), which stops at the first zero. A reader that reads to the end of the file reads all of the zeros.

All public methods are thread-safe. One mutex guards the mapped view, the line index and the file handle, so two threads cannot copy to the same offset, and readLogs() never sees a half-written line. Node::log() can run on any thread that holds the node, while a LogWidget reads on the GUI thread. The class emits logChanged() after it releases the lock, and prints its own warnings after it releases the lock. So a slot or a message handler that calls back into the same LogStorage does not deadlock.

The lock is per instance. Two LogStorage instances that map the same day file do not share it.