Welcome to Software Development on Codidact!

Will you help us build our independent community of developers helping developers? We're small and trying to grow. We welcome questions about all aspects of software development, from design to code to QA and more. Got questions? Got answers? Got code you'd like someone to review? Please join us.

Review Suggested Edit

You can't approve or reject suggested edits because you haven't yet earned the Edit Posts ability.

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:
~~@dmckee‭ Sorry, I tried to post a comment but failed. I could click "post" but the comment didn't appear.~~
Your solution is how I have solved it currently (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?

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](https://software.codidact.com/users/52997)
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?

c++ qt QFile QThread QTextStream

Communities

Review Suggested Edit