gethostbyname thread safe?!

[devshlom]

Hi,

I'm using the gethostbyname function in my code, which is compiled on different UNIXs (AIX,HP, Linux, Solaris, etc.)
I found in the web people that say that this function is thread safe on some OS versions (HPUX 11, AIX 5... )
I must confirm this issue, so...
1. I need to know if this function is a thread safe on HPUX and if so, what is the minmal version for this safety?!
2. I read in HP documentation (http://docs.hp.com/en/B3921-90010/thread_safety.5.html) - what is the meaning of "Cancel Safe"? since this function is under this criteria.

tx in advance,
Shlom

[Steven Schweda]

> (HPUX 11, AIX 5... )

HP-UX "11" is not a precise description of an
HP-UX version.

I know nothing, but, resorting to the
painfully obvious "man gethostbyname" on an
HP-UX 11.31 PA-RISC system, I pretty easily
found a section which begins:

In a multithreaded application, [...]

and which seems to provide all the
thread-related info _I_'d ever want.

If you don't have an HP-UX system where you
can do this, try:

http://www.testdrive.hp.com/

Systems are available back to HP-UX 11.11.

[Dennis Handly]

>what is the meaning of "Cancel Safe"?

It means that if you use pthread_cancel, everything is predictable.

[devshlom]

Hi,

1. Risc 11.23
2. Dennis, I didn't understand your answer - can you give more details please?! Actually, if you have some source that says that gethostbyname is thread safe on HPUX 11.23 (or not...) it would be better.

tx again.

[Dennis Handly]

>1. PA-RISC 11.23

Your 11.11 document says it is thread safe. So does 11.23:
http://docs.hp.com/en/B3921-60631/thread_safety.5.html

>2. I didn't understand your answer - can you give more details please?

It is thread safe. It is also non-asynchronous cancel safe.

>if you have some source that says that gethostbyname is thread safe on HPUX 11.23

You have the source, thread_safety(5).
And as Steven said see "multithreaded application" in gethostent(3N).

[devshlom]

Dennis,
tx again for giving me the answer - I understand now that this is a thread safe function.

Now, for my general info:
I still don't understand the meaning of "Cancel-Safe"...
If a function is Cancel-Safe one, so it's a ____________________________

shlom

[Dennis Handly · Accepted solution]

>I still don't understand the meaning of "Cancel-Safe".

See pthread_cancel(3T):
http://docs.hp.com/en/B2355-60130/pthread_cancel.3T.html

It means the thread can be terminated in a controlled manner and doesn't leave resources lying around and possibly leave mutexes locked.

[devshlom]

Tx!

[rick jones]

Now that you are confident that gethostbyname() is thread-safe and all, I will point-out that new work or contemporary rework of existing code should be using getaddrinfo() and friends rather than gethostbyname() :)

Among other things, getaddrinfo() enables retrieval of IPv6 addresses and can make a few things easier even with IPv4 addresses. At least that was my impression after making the necessary modifications to the netperf benchmark sources.