CODEWITHSUNDEEP
clinuxmultithreadingpthreads
Ajith C Narayanan
Ajith C Narayanan

Reputation: 616

Can I make the file descriptor limit a per-thread limit?

I am working on a Centos-6 x86_64 machine. By default, if I start a process, it can open 1024 files (including the standard in/out/error streams) and I am able to extend that limit using setrlimit() APIs.

My problem is that if I start a thread within the process, it shares this limit. For example, assume I am running a parent process which opens 1024 descriptors, and then if I create one thread using pthread_create(), it can't open a single file because its parent already opened 1024 descriptors and consumed the full limit.

I want to make the child thread (not child process) able to open 1024 files like its parent. I know that extending parent's file descriptor limit to 2048 will allow the child to open 1024 more files. But I want to make the parent and child have individual limits, not a shared limit.

I am expecting some attributes in pthread_attr_t that can be applicable for the child thread to have an individual file table.

Upvotes: 1

Views: 1086

Answers (1)

Petr Skocik
Petr Skocik

Reputation: 60137

On Linux, 

unshare(CLONE_FILES);

(if successful) will give the current thread its own filedescriptor table.

It should be usable from an already- spawned kernel-backed (all Linux pthreads implementations I know of) pthread.

There doesn't appear to be even a nonportable pthread attribute that you could set this up with, but you can use the above approach to wrap pthread_create, adding this capability.

If you're doing your own threading on Linux, you can pass the CLONE_FILES flag directly to clone. Otherwise you'll need the to make your wrapped_pthread_create wait until the child has made the unshare call (and cancel and reap the thread if the call failed).

Upvotes: 4

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