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Comments on Write to same file from multiple threads
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Write to same file from multiple threads
I want to write a text file from multiple threads. The file structure is line-oriented. This means writing of lines should be atomic. I am using Qt 5.15.2.
Is it enough to protect a shared QTextStream/QFile pair using a QMutex?
EDIT:
For now using dmckee's solution I have solved it (well, a bit more complex but it boils down exactly to your idea). However moving the file work into a single writer thread does not scale.
I have a lot of threads writing very big amounts of data. This means the writer thread receives a big load and (more important) queued events need to carry a lot of data (which means a lot of RAM consumption). This gets even more nasty in case the writer thread is too slow. It will pile up events consuming virtually all RAM in the system. This is why I would prefer a mutex like solution very much. Alas, is that possible?
Post
Because you are using Qt in particular there is something to be said for not solving this problem yourself.
Instead, create a single object that owns the stream or file and offers a writeLine slot. In the simplest case the signature might be writeLine(const QString & line). Then your threads simple signal the owner with the data they want to write and the Qt engine takes care of the locking for you.
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