Solved

Concurrent read / write of serial port

Posted on 2006-07-14
4
521 Views
Last Modified: 2010-04-21
I have a serial port access class which wraps the termios API. This serial port in some situations is used in a multithreaded environment. In this case it will be shared by 2 threads but I can guarantee that 1 will perform output only, and the other will perform input only. Does this require a mutex to access the object?

I can't find any documentation on the thread-safety of read(2) and write(2), or termios(3). I guess it really depends on the implementation, but given that read, write and the termios API are POSIX-compliant, does anyone know if POSIX specifies the thread-safety of these functions?

--Rob
0
Comment
Question by:boycy
  • 2
  • 2
4 Comments
 
LVL 8

Expert Comment

by:manish_regmi
ID: 17106913
> does anyone know if POSIX specifies the thread-safety of these functions?

No the POSIX does not say anything about thread safety of those functions. This means that thread safety is not guranteed and one should assume that they are not thread safe.

> Does this require a mutex to access the object?
At the hardware level, Serial ports have seperate pins for data transmission and reception.
So, you may not need to protect read from writes.

regards
Manish Regmi
0
 
LVL 6

Author Comment

by:boycy
ID: 17106951
Granted the hardware level is fine for concurrent read/write - after all, it is full duplex. I would *assume* that providing an API which removes this full duplex ability would be a really silly idea; however assumptions are not good things. If there is any doubt at all as to whether these functions are thread-safe then I cannot use them. I'm having real trouble finding any information on this subject.
0
 
LVL 8

Accepted Solution

by:
manish_regmi earned 125 total points
ID: 17106982
A discussion on red hat forum also suggests it is safe.

http://sources.redhat.com/ml/ecos-discuss/2006-04/msg00219.html
So under Linux it may be safe but may not be for other OS.

Also since POSIX does not confirm thread safety. You can protect them with mutex for safety.

regards
Manish Regmi
0
 
LVL 6

Author Comment

by:boycy
ID: 17107000
Manish, thanks :)
0

Featured Post

Master Your Team's Linux and Cloud Stack!

The average business loses $13.5M per year to ineffective training (per 1,000 employees). Keep ahead of the competition and combine in-person quality with online cost and flexibility by training with Linux Academy.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

The purpose of this article is to fix the unknown display problem in Linux Mint operating system. After installing the OS if you see Display monitor is not recognized then we can install "MESA" utilities to fix this problem or we can install additio…
The purpose of this article is to demonstrate how we can upgrade Python from version 2.7.6 to Python 2.7.10 on the Linux Mint operating system. I am using an Oracle Virtual Box where I have installed Linux Mint operating system version 17.2. Once yo…
This Micro Tutorial will teach you how to censor certain areas of your screen. The example in this video will show a little boy's face being blurred. This will be demonstrated using Adobe Premiere Pro CS6.
Microsoft Active Directory, the widely used IT infrastructure, is known for its high risk of credential theft. The best way to test your Active Directory’s vulnerabilities to pass-the-ticket, pass-the-hash, privilege escalation, and malware attacks …

803 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question