[ace-users] Thread safe singleton class example with ACE

[Douglas C. Schmidt]

Hi Ramesh,

The typical way of getting a thread-safe singleton is to use

typedef ACE_Singleton <Your_Class_Goes_Here, ACE_SYNCH_RECURSIVE_MUTEX> MY_SINGLETON;

There are various examples of this in ACE_ROOT/tests if you search for
ACE_Singleton.

Take care,

Doug

I am a newbie to ACE, is there a thread-safe singleton implementation
example in the ACE tarball? I havent exhausted searching the book yet,
but checking to know if there is something already there in the
examples - which I can look at and understand. BTW I have the 5.6.5
version of ace installed.
Thanks
/R

[T0mServ0]

Since ACE uses a template for the ACE_Singleton type, would this be a
problem when other DLL's in the same process try to use it?

For example:

Let's suppose there is a DLL called libmysingleton.so which actually
implements the singleton in question (we'll call it MySingleton).

There is a common header file which defines the singleton like so
(MySingleton.h):

class MySingleton
{
friend class ACE_Singleton<MySingleton, ACE_Recursive_Thread_Mutex>;
public:
void test();

private:
MySingleton();
~MySingleton();
};
typdef ACE_Singleton<MySingleton, ACE_Recursive_Thread_Mutex> MYSINGLETON;

Now let's say I have another DLL called libtest2.so which has some code
which USES the singleton (anywhere in the code doesn't matter):

... MYSINGLETON::instance()->test(); ...

And I have created an EXE called test which links with libtest2.so and
libmysingleton.so, and in the test source I also use the singleton:

... MYSINGLETON::instance()->test();

The test source, libtest2.so source, and libmysingleton.so source all share
the same common header file MySingleton.h.

The problem I'm seeing is that if I understand templates correctly, if each
separate module shares the same header file, there will be multiple
instances of the MYSINGLETON created due to the templates.
I have a printf() statement in the constructor of MySingleton() which indeed
tells me that more than one instance of MySingleton is created when I run
the test program. The instance in just the test module is created first,
and when libtest2.so uses it, a new instance is created there too.

Now, is there anything or compiler flag I need to be using to prevent this?
Or do you see anything else wrong or any changes I could make to make
certain that only one instance of MySingleton is ever created under one
process?

Thanks!
Brandon

Post by Douglas C. Schmidt
Hi Ramesh,
The typical way of getting a thread-safe singleton is to use
typedef ACE_Singleton <Your_Class_Goes_Here, ACE_SYNCH_RECURSIVE_MUTEX> MY_SINGLETON;
There are various examples of this in ACE_ROOT/tests if you search for
ACE_Singleton.
Take care,
Doug

I am a newbie to ACE, is there a thread-safe singleton implementation
example in the ACE tarball? I havent exhausted searching the book yet,
but checking to know if there is something already there in the
examples - which I can look at and understand. BTW I have the 5.6.5
version of ace installed.
Thanks
/R

--
Dr. Douglas C. Schmidt Professor and Associate Chair
Electrical Engineering and Computer Science TEL: [phone]
www.dre.vanderbilt.edu/~schmidt

...

[T0mServ0]

Apologies,

I meant to say that I'm seeing this issue on Linux Redhat which has GCC
4.2.4. I'm using ACE 5.6.5.

Brandon

Post by T0mServ0
Since ACE uses a template for the ACE_Singleton type, would this be a
problem when other DLL's in the same process try to use it?
Let's suppose there is a DLL called libmysingleton.so which actually
implements the singleton in question (we'll call it MySingleton).
There is a common header file which defines the singleton like so
class MySingleton
{
friend class ACE_Singleton<MySingleton, ACE_Recursive_Thread_Mutex>;
void test();
MySingleton();
~MySingleton();
};
typdef ACE_Singleton<MySingleton, ACE_Recursive_Thread_Mutex> MYSINGLETON;
Now let's say I have another DLL called libtest2.so which has some code
... MYSINGLETON::instance()->test(); ...
And I have created an EXE called test which links with libtest2.so and
... MYSINGLETON::instance()->test();
The test source, libtest2.so source, and libmysingleton.so source all
share the same common header file MySingleton.h.
The problem I'm seeing is that if I understand templates correctly, if
each separate module shares the same header file, there will be multiple
instances of the MYSINGLETON created due to the templates.
I have a printf() statement in the constructor of MySingleton() which
indeed tells me that more than one instance of MySingleton is created when
I run the test program. The instance in just the test module is created
first, and when libtest2.so uses it, a new instance is created there too.
Now, is there anything or compiler flag I need to be using to prevent
this? Or do you see anything else wrong or any changes I could make to
make certain that only one instance of MySingleton is ever created under
one process?
Thanks!
Brandon

Post by Douglas C. Schmidt
Hi Ramesh,
The typical way of getting a thread-safe singleton is to use
typedef ACE_Singleton <Your_Class_Goes_Here, ACE_SYNCH_RECURSIVE_MUTEX> MY_SINGLETON;
There are various examples of this in ACE_ROOT/tests if you search for
ACE_Singleton.
Take care,
Doug

I am a newbie to ACE, is there a thread-safe singleton implementation
example in the ACE tarball? I havent exhausted searching the book yet,
but checking to know if there is something already there in the
examples - which I can look at and understand. BTW I have the 5.6.5
version of ace installed.
Thanks
/R

--
Dr. Douglas C. Schmidt Professor and Associate Chair
Electrical Engineering and Computer Science TEL: [phone]
www.dre.vanderbilt.edu/~schmidt

...

[T0mServ0]

I narrowed down the issue to understand that it has something to do with
the -fvisibility=hidden and -fvisibility-inlines-hidden flags. I do have
the MySingleton class "exported":

class __attribute__((visibility("default"))) MySingleton
{
......
};

I'll keep playing around with it...

If I take out the -fvisibility=hidden -fvisibility-inlines-hidden flags,
only one copy of the singleton class created.

Brandon

Post by T0mServ0
Since ACE uses a template for the ACE_Singleton type, would this be a
problem when other DLL's in the same process try to use it?
Let's suppose there is a DLL called libmysingleton.so which actually
implements the singleton in question (we'll call it MySingleton).
There is a common header file which defines the singleton like so
class MySingleton
{
friend class ACE_Singleton<MySingleton, ACE_Recursive_Thread_Mutex>;
void test();
MySingleton();
~MySingleton();
};
typdef ACE_Singleton<MySingleton, ACE_Recursive_Thread_Mutex> MYSINGLETON;
Now let's say I have another DLL called libtest2.so which has some code
... MYSINGLETON::instance()->test(); ...
And I have created an EXE called test which links with libtest2.so and
... MYSINGLETON::instance()->test();
The test source, libtest2.so source, and libmysingleton.so source all
share the same common header file MySingleton.h.
The problem I'm seeing is that if I understand templates correctly, if
each separate module shares the same header file, there will be multiple
instances of the MYSINGLETON created due to the templates.
I have a printf() statement in the constructor of MySingleton() which
indeed tells me that more than one instance of MySingleton is created when
I run the test program. The instance in just the test module is created
first, and when libtest2.so uses it, a new instance is created there too.
Now, is there anything or compiler flag I need to be using to prevent
this? Or do you see anything else wrong or any changes I could make to
make certain that only one instance of MySingleton is ever created under
one process?
Thanks!
Brandon

Post by Douglas C. Schmidt
Hi Ramesh,
The typical way of getting a thread-safe singleton is to use
typedef ACE_Singleton <Your_Class_Goes_Here, ACE_SYNCH_RECURSIVE_MUTEX> MY_SINGLETON;
There are various examples of this in ACE_ROOT/tests if you search for
ACE_Singleton.
Take care,
Doug

I am a newbie to ACE, is there a thread-safe singleton implementation
example in the ACE tarball? I havent exhausted searching the book yet,
but checking to know if there is something already there in the
examples - which I can look at and understand. BTW I have the 5.6.5
version of ace installed.
Thanks
/R

--
Dr. Douglas C. Schmidt Professor and Associate Chair
Electrical Engineering and Computer Science TEL: [phone]
www.dre.vanderbilt.edu/~schmidt

...

[Johnny Willemsen]

Hi,

Check ace/Based_Pointer_Repository.h for a singleton where there is one
instance per process.

Regards,


Johnny Willemsen
Remedy IT
Postbus 101
2650 AC  Berkel en Rodenrijs
The Netherlands
www.theaceorb.nl / www.remedy.nl 

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http://scoreboard.theaceorb.nl ***
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http://www.theaceorb.nl ***

Post by T0mServ0
Since ACE uses a template for the ACE_Singleton type, would this be a
problem when other DLL's in the same process try to use it?
Let's suppose there is a DLL called libmysingleton.so which actually
implements the singleton in question (we'll call it MySingleton).
There is a common header file which defines the singleton like so
class MySingleton
{
friend class ACE_Singleton<MySingleton, ACE_Recursive_Thread_Mutex>;
void test();
MySingleton();
~MySingleton();
};
typdef ACE_Singleton<MySingleton, ACE_Recursive_Thread_Mutex> MYSINGLETON;
Now let's say I have another DLL called libtest2.so which has some code
... MYSINGLETON::instance()->test(); ...
And I have created an EXE called test which links with libtest2.so and
... MYSINGLETON::instance()->test();
The test source, libtest2.so source, and libmysingleton.so source all

...

share

Post by T0mServ0
the same common header file MySingleton.h.
The problem I'm seeing is that if I understand templates correctly, if

each

Post by T0mServ0
separate module shares the same header file, there will be multiple
instances of the MYSINGLETON created due to the templates.
I have a printf() statement in the constructor of MySingleton() which

indeed

Post by T0mServ0
tells me that more than one instance of MySingleton is created when I run
the test program. The instance in just the test module is created first,
and when libtest2.so uses it, a new instance is created there too.
Now, is there anything or compiler flag I need to be using to prevent

this?

Post by T0mServ0
Or do you see anything else wrong or any changes I could make to make
certain that only one instance of MySingleton is ever created under one
process?
Thanks!
Brandon

Post by Douglas C. Schmidt
Hi Ramesh,
The typical way of getting a thread-safe singleton is to use
typedef ACE_Singleton <Your_Class_Goes_Here, ACE_SYNCH_RECURSIVE_MUTEX>
MY_SINGLETON;
There are various examples of this in ACE_ROOT/tests if you search for
ACE_Singleton.
Take care,
Doug

I am a newbie to ACE, is there a thread-safe singleton implementation
example in the ACE tarball? I havent exhausted searching the book yet,
but checking to know if there is something already there in the
examples - which I can look at and understand. BTW I have the 5.6.5
version of ace installed.
Thanks
/R

--
Dr. Douglas C. Schmidt Professor and Associate

...

Chair

Post by T0mServ0

Post by Douglas C. Schmidt
Electrical Engineering and Computer Science TEL: [phone]
www.dre.vanderbilt.edu/~schmidt

***@vanderbilt.edu