Is malloc() function provided in <stdlib.h> thread-safe?

[climber.cui@gmail.com]

Hi all,
Does anyone have experience on the thread-safty issue with malloc()?
Some people said this function provided in stdlib.h is not thread-
safe, but someone said it is thread safe. Is it possible this
function evolves from thread-unsafe to thread-safe in recent years?
How could i find out?
I am using the C library coming with GNU linux distribution.

thanks a lot.

tony

[Walter Roberson]

Re: Is malloc() function provided in &lt;stdlib.h&gt ; thread-safe?

In article <b8e707eb-b353-41d7-82c0-5f62f362514c@27 g2000hsf.google groups.com>,
<climber.cui@gm ail.comwrote:

Does anyone have experience on the thread-safty issue with malloc()?
>Some people said this function provided in stdlib.h is not thread-
>safe, but someone said it is thread safe. Is it possible this
>function evolves from thread-unsafe to thread-safe in recent years?
>How could i find out?

The C standards have no concept of threads or thread safety, so
unless you define threads vacuously, one must assume that there
will be platforms on which malloc() is *not* thread safe.

I am using the C library coming with GNU linux distribution.

If you want to know about whether malloc() is thread-safe in the
particular distribution you are using, then ask in a newsgroup
or mailing list that deals with that particular distribution.
The answer for C as a whole is "NO". It could be that the
answer for all platforms that you are interested in is "Yes", but
that would be due to implementation-specific behaviour, not behaviour
mandated by C.
--
"For men are prone to go it blind along the calf-paths of the
mind To do what other men have done. They follow in the beaten
track, and out and in, and forth and back, and still their
devious course pursue, to keep the path that others do." -- Sam Walter Foss

[Ian Collins]

Re: Is malloc() function provided in &lt;stdlib.h&gt ; thread-safe?

climber.cui@gma il.com wrote:

Hi all,
Does anyone have experience on the thread-safty issue with malloc()?
Some people said this function provided in stdlib.h is not thread-
safe, but someone said it is thread safe. Is it possible this
function evolves from thread-unsafe to thread-safe in recent years?
How could i find out?
I am using the C library coming with GNU linux distribution.
>

Then check your man pages.

--
Ian Collins.

[Lew Pitcher]

Re: Is malloc() function provided in &lt;stdlib.h&gt ; thread-safe?

In comp.lang.c, climber.cui@gma il.com wrote:

Hi all,
Does anyone have experience on the thread-safty issue with malloc()?

Possibly. In any case, "thread-safety" is irrelevant here. The C standard
does not include "threads", and does not address whether a specific library
function is "thread-safe" or not.

However, your C compiler /implementation/ may recognize "threads" in your
environment. To determine if your /implementation/ supplies "thread-safe"
standard library functions, you should check your /implementation' s/
documentation or ask about the subject in the appropriate /implementation/
forum.

Some people said this function provided in stdlib.h

stdlib.h does not provide any function. It provides function declarations
(prototypes for the function's calling parameters and return value),
macros, and other sort of information. The /function/ will be provided in
one of your implementation' s libraries.

is not thread-safe, but someone said it is thread safe.

"Some people" "Someone"? How about asking the implementers, or checking the
implementation documentation? Remember, even here, we are "some people",
and I am "someone".

Is it possible this
function evolves from thread-unsafe to thread-safe in recent years?

It is, in any specific implementation. An implementation can even offer both
thread-safe and thread-unsafe versions of the same function, so long as the
mechanism that selects the function is outside of the C language (like a
compiler or linker option, or the specification of an alternate library
during linkage).

How could i find out?

Read your compiler's documentation. Read the documentation on your runtime.

I am using the C library coming with GNU linux distribution.

<OT>
Assuming a recent version of GCC and a recent implementation of Linux, you
have may have
1) no threading support at all,
2) "Linux threads" support, or
3) "NPTL" threads support

"Linux Threads" and "NPTL threads" runtimes are implemented in different
(non-C-standard) libraries, which provide both the threading primative
functions and (possibly) "thread-safe" replacement functions for some
thread-unsafe functions in the standard and POSIX libraries.

If your environment does not include either "Linux Threads" or "NPTL"
threads, then you likely have a C runtime library that does not recognize
threads, and thus has a questionable "thread-safety" (functions /may/ be
thread-safe, but there is no guarantee). Check your /usr/doc/gcc*
documentation, and the manpage for each function you intend to use, and
look for the instructions on how to use the appropriate threading library.
</OT>

thanks a lot.
>
tony

--
Lew Pitcher

Master Codewright & JOAT-in-training | Registered Linux User #112576
http://pitcher.digitalfreehold.ca/ | GPG public key available by request
---------- Slackware - Because I know what I'm doing. ------

[Paul Hsieh]

Re: Is malloc() function provided in &lt;stdlib.h&gt ; thread-safe?

On Apr 25, 1:12 pm, climber....@gma il.com wrote:

Hi all,
Does anyone have experience on the thread-safty issue with malloc()?

Yes. To implement a thread without a thread-safe malloc is a
practically meaningless concept. Any system which does not support
this, cannot seriously call itself supporting of multi-threading.

Some people said this function provided in stdlib.h is not thread-
safe, but someone said it is thread safe.

Some compilers come with thread-safe versus non-thread-safe standard
libraries. Check your documentation.

[...] Is it possible this
function evolves from thread-unsafe to thread-safe in recent years?

As I said, a multi-threading environment without a thread-safe malloc
is basically a worthless and unusable environment. Typically, malloc/
free etc is designed to be thread safe, then the threads themselves
allocate their auto space and return stack space via an malloc. So
you can see that the two concepts of memory management and thread
management as dependent on each other. You can't really have one
without the other in a multi-threading environment.

How could i find out?
I am using the C library coming with GNU linux distribution.

Certainly gcc is thread-safe.

--
Paul Hsieh

http://www.pobox.com/~qed/

http://bstring.sf.net/

[Herbert Rosenau]

Re: Is malloc() function provided in &lt;stdlib.h&gt ; thread-safe?

On Fri, 25 Apr 2008 20:12:46 UTC, climber.cui@gma il.com wrote:

Hi all,
Does anyone have experience on the thread-safty issue with malloc()?
Some people said this function provided in stdlib.h is not thread-
safe, but someone said it is thread safe. Is it possible this
function evolves from thread-unsafe to thread-safe in recent years?
How could i find out?
I am using the C library coming with GNU linux distribution.

On my implementation malloc is threadsave - or not. It depends simply
on the library bounded to the the executeable.

The implementation serves the same functionality in 4 different
libraries:
1. single CPU, single threaded
highly optimised under the premise that the application runs only
for its own using only one thread on one CPU
The process using this library has no interaction outside its
own single threaded process.
2. single CPU, multithreaded
highly optimised under the premise that the app has no need to
coordinate multiple CPUs but can run multiple threads sharing the
same CPU
3. multiple CPU, singlethreaded
highly optimised under the premise that the app has no need to
run multiple threads of its own but my have the need to
coordinate with other app running on other CPU
4. multiple CPU, multithreaded
data can be shared between multiple CPUs running multiple threads.

So the developer tells the linker which of the library variant he
needs.

--
Tschau/Bye
Herbert

Visit http://www.ecomstation.de the home of german eComStation
eComStation 1.2R Deutsch ist da!

[CBFalconer]

Re: Is malloc() function provided in &lt;stdlib.h&gt ; thread-safe?

Paul Hsieh wrote:

climber....@gma il.com wrote:
>

>Does anyone have experience on the thread-safty issue with malloc()?

>

.... snip ...

>

>[...] Is it possible this
>function evolves from thread-unsafe to thread-safe in recent years?

>
As I said, a multi-threading environment without a thread-safe malloc
is basically a worthless and unusable environment. Typically, malloc/
free etc is designed to be thread safe, then the threads themselves
allocate their auto space and return stack space via an malloc. So
you can see that the two concepts of memory management and thread
management as dependent on each other. You can't really have one
without the other in a multi-threading environment.

It is perfectly possible to use a non-thread-safe malloc in a
thread-safe manner. It is necessary that the OS have a system call
that will prevent thread changes, say "thread_lock()" . This will
also require a corresponding call, say "thread_unlock( )".

Then, to use anything in the malloc group, you simply write:

thread_lock();
p = malloc(N * sizeof *p);
thread_unlock() ;

and you have pushed all the hard stuff off to the system designer.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.


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[CBFalconer]

Re: Is malloc() function provided in &lt;stdlib.h&gt ; thread-safe?

climber.cui@gma il.com wrote:

>
Does anyone have experience on the thread-safty issue with malloc()?
Some people said this function provided in stdlib.h is not thread-
safe, but someone said it is thread safe. Is it possible this
function evolves from thread-unsafe to thread-safe in recent years?
How could i find out?
>
I am using the C library coming with GNU linux distribution.

That depends on the system and the library. It is probably not
thread-safe. It probably is process-safe, because a different
process normally has a different memory map. Neither is covered in
the C standard, so this does not affect C standard compatibility.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.


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[Antoninus Twink]

Re: Is malloc() function provided in &lt;stdlib.h&gt ; thread-safe?

On 25 Apr 2008 at 22:33, CBFalconer wrote:

Paul Hsieh wrote:

>climber....@gm ail.com wrote:
>>

>>Does anyone have experience on the thread-safty issue with malloc()?

>>
>As I said, a multi-threading environment without a thread-safe malloc
>is basically a worthless and unusable environment. Typically, malloc/
>free etc is designed to be thread safe, then the threads themselves
>allocate their auto space and return stack space via an malloc. So
>you can see that the two concepts of memory management and thread
>management as dependent on each other. You can't really have one
>without the other in a multi-threading environment.

>
It is perfectly possible to use a non-thread-safe malloc in a
thread-safe manner. It is necessary that the OS have a system call
that will prevent thread changes, say "thread_lock()" . This will
also require a corresponding call, say "thread_unlock( )".
>
Then, to use anything in the malloc group, you simply write:
>
thread_lock();
p = malloc(N * sizeof *p);
thread_unlock() ;
>
and you have pushed all the hard stuff off to the system designer.

You really don't have the first, tiniest inkling of a clue what you're
talking about, do you?

To the OP, please listen to the common-sense words of Paul Hsieh quoted
above. *Of course* there isn't a single C threads implementation that
doesn't come with a threadsafe malloc(): what would be the point of
using threads if the cost was not being able to do something as
fundamental as allocating memory?

[Richard]

Re: Is malloc() function provided in &lt;stdlib.h&gt ; thread-safe?

Antoninus Twink <nospam@nospam. invalidwrites:

On 25 Apr 2008 at 22:33, CBFalconer wrote:

>Paul Hsieh wrote:

>>climber....@g mail.com wrote:
>>>
>>>Does anyone have experience on the thread-safty issue with malloc()?
>>>
>>As I said, a multi-threading environment without a thread-safe malloc
>>is basically a worthless and unusable environment. Typically, malloc/
>>free etc is designed to be thread safe, then the threads themselves
>>allocate their auto space and return stack space via an malloc. So
>>you can see that the two concepts of memory management and thread
>>management as dependent on each other. You can't really have one
>>without the other in a multi-threading environment.

>>
>It is perfectly possible to use a non-thread-safe malloc in a
>thread-safe manner. It is necessary that the OS have a system call
>that will prevent thread changes, say "thread_lock()" . This will
>also require a corresponding call, say "thread_unlock( )".
>>
>Then, to use anything in the malloc group, you simply write:
>>
> thread_lock();
> p = malloc(N * sizeof *p);
> thread_unlock() ;
>>
>and you have pushed all the hard stuff off to the system designer.

>
You really don't have the first, tiniest inkling of a clue what you're
talking about, do you?

I find it astonishing that he is tolerated at all by the regs. He is a
typical know nothing blow hard where a little bit of knowledge shows
itself to be a very dangerous thing. Second only to Default User in
useless net nanny posts I wonder what it is that makes him post at
all.

>
To the OP, please listen to the common-sense words of Paul Hsieh quoted
above. *Of course* there isn't a single C threads implementation that
doesn't come with a threadsafe malloc(): what would be the point of
using threads if the cost was not being able to do something as
fundamental as allocating memory?

Exactly. But maybe Falconer is being thick on purpose - he can state
that he is not a "threads guy" and that they are dealt with down the
"corridor on the right".

[=?iso-8859-1?Q?=D8yvind_R=F8tvold?=]

Re: Is malloc() function provided in &lt;stdlib.h&gt ; thread-safe?


"Herbert Rosenau" <os2guy@pc-rosenau.dewrite s:

[ ... ]

1. single CPU, single threaded
highly optimised under the premise that the application runs only
for its own using only one thread on one CPU
The process using this library has no interaction outside its
own single threaded process.

[ ... ]

3. multiple CPU, singlethreaded
highly optimised under the premise that the app has no need to
run multiple threads of its own but my have the need to
coordinate with other app running on other CPU

Just curious here, what's the difference between these two? How does
coordintaion with other treads affect malloc?


--
... __o Øyvind
... _`\(, http://www.darkside.no/olr/
... (_)/(_) ... biciclare necesse est ...

[Walter Roberson]

Re: Is malloc() function provided in &lt;stdlib.h&gt ; thread-safe?

In article <slrng16mtk.5i9 .nospam@nospam. invalid>,
Antoninus Twink <nospam@nospam. invalidwrote:

>>climber....@g mail.com wrote:
>>>Does anyone have experience on the thread-safty issue with malloc()?

>*Of course* there isn't a single C threads implementation that
>doesn't come with a threadsafe malloc(): what would be the point of
>using threads if the cost was not being able to do something as
>fundamental as allocating memory?

The original poster asked a general question about thread-safety
in malloc(), not one restricted to systems with threads implementations .
--
"I buy more from my grocer than he buys from me, and I bet it's
the same with you and your grocer. That means we have a trade
deficit with our grocers. Does our perpetual grocer trade deficit
portend doom?" -- Walter Williams

[ymuntyan@gmail.com]

Re: Is malloc() function provided in &lt;stdlib.h&gt ; thread-safe?

On Apr 26, 2:18 pm, rober...@ibd.nr c-cnrc.gc.ca (Walter Roberson)
wrote:

In article <slrng16mtk.5i9 .nos...@nospam. invalid>,
Antoninus Twink <nos...@nospam. invalidwrote:
>

>climber....@gm ail.com wrote:
>>Does anyone have experience on the thread-safty issue with malloc()?

*Of course* there isn't a single C threads implementation that
doesn't come with a threadsafe malloc(): what would be the point of
using threads if the cost was not being able to do something as
fundamental as allocating memory?

>
The original poster asked a general question about thread-safety
in malloc(), not one restricted to systems with threads implementations .

Amazing. You could tell that OP *could* ask about
nonsense like that (we are in comp.lang.c, so we
may not assume that the OP is not dumb, right? He
could be dumb, "we don't know"). But claiming that
he *did* ask such a stupid thing is a little too
much, isn't it?

Yevgen

[Ian Collins]

Re: Is malloc() function provided in &lt;stdlib.h&gt ; thread-safe?

CBFalconer wrote:

climber.cui@gma il.com wrote:

>Does anyone have experience on the thread-safty issue with malloc()?
>Some people said this function provided in stdlib.h is not thread-
>safe, but someone said it is thread safe. Is it possible this
>function evolves from thread-unsafe to thread-safe in recent years?
>How could i find out?
>>
>I am using the C library coming with GNU linux distribution.

>
That depends on the system and the library. It is probably not
thread-safe.

What brings you to that conclusion? An environment with threads but
without a thread safe malloc would be about as much use as a fart in a
wetsuit.

--
Ian Collins.

[CBFalconer]

Re: Is malloc() function provided in &lt;stdlib.h&gt ; thread-safe?

Ian Collins wrote:

CBFalconer wrote:

>climber.cui@gma il.com wrote:
>>

>>Does anyone have experience on the thread-safty issue with malloc()?
>>Some people said this function provided in stdlib.h is not thread-
>>safe, but someone said it is thread safe. Is it possible this
>>function evolves from thread-unsafe to thread-safe in recent years?
>>How could i find out?
>>>
>>I am using the C library coming with GNU linux distribution.

>>
>That depends on the system and the library. It is probably not
>thread-safe.

>
What brings you to that conclusion? An environment with threads but
without a thread safe malloc would be about as much use as a fart in
a wetsuit.

Both are useful. For malloc, consider putting all the malloc
(free, calloc, realloc) calls in just one thread. Don't confuse
threads and processes, which are all OT here.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.


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