Using pthread_t as a key in a map

classic Classic list List threaded Threaded
7 messages Options
Reply | Threaded
Open this post in threaded view
|

Using pthread_t as a key in a map

Paolo Brandoli
I have a source code that uses the pthread_t as a key in a std::map.
Because pthread-win32 defines pthread_t as a structure, the compilation fails.

I added the following lines in my pthread.h header in order to allow
the usage of pthread_t in the map:

bool operator < (const ptw32_handle_t& left, const ptw32_handle_t& right)
{
    return left.p < right.p;
}

bool operator > (const ptw32_handle_t& left, const ptw32_handle_t& right)
{
    return left.p > right.p;
}

Bye
Paolo Brandoli
http://www.puntoexe.com
Reply | Threaded
Open this post in threaded view
|

Re: Using pthread_t as a key in a map

Will Bryant-2
Hi Paolo,

Bear in mind that pthreads-win32 is written in C, and operator
overloading is a C++ feature, so adding that would prevent
pthreads-win32 from compiling with C apps.

One alternative is to make a custom comparator type and use that in the
map declaration - or you could even simply move those operator overloads
to your own units (they don't have to be defined where the type being
compared is declared, as long as they've visible at the point where
they're used - ie. your map declaration).

But bear in mind that in any case, making use of the ptw32_handle_t type
makes your code nonportable, and since portability is generally the
reason one is using pthreads-win32 in the first place, this is perhaps
not the best design for general use.

Will


Paolo Brandoli wrote:

> I have a source code that uses the pthread_t as a key in a std::map.
> Because pthread-win32 defines pthread_t as a structure, the
> compilation fails.
>
> I added the following lines in my pthread.h header in order to allow
> the usage of pthread_t in the map:
>
> bool operator < (const ptw32_handle_t& left, const ptw32_handle_t& right)
> {
>    return left.p < right.p;
> }
>
> bool operator > (const ptw32_handle_t& left, const ptw32_handle_t& right)
> {
>    return left.p > right.p;
> }
>
> Bye
> Paolo Brandoli
> http://www.puntoexe.com
>


--
Will Bryant



Reply | Threaded
Open this post in threaded view
|

Re: Using pthread_t as a key in a map

Paolo Brandoli
Hi Will,

What I'm trying to do is to order the pthread_t pointers so I can
simulate the windows function "WaitForMultipleObjects"; I have to
order the pthread_t in a consistent way before attempting to lock
several mutexes at once.

The way the pthread_t is defined in the library doesn't allow to use
the < and > operators; those operators can be used when pthread_t is
defined as a pointer (like in the pthreads implementation on posix
systems) and not as a structure containing a pointer (as in
win32-pthread).

I defined the operator for ptw32_handle_t, but it works for pthread_t
(since it is a synonim for ptw32_handle_t).

Anyway your considerations are right since this breaks the compilation
on C compilers. On C++ compilers it just remove the errors when I try
to compare two pthread_t values.

I'm trying to find a more elegant solution, but I'm just staring at
the monitor and nothing pops up in my brain.

Paolo Brandoli

On 5/15/06, Will Bryant <[hidden email]> wrote:

> Hi Paolo,
>
> Bear in mind that pthreads-win32 is written in C, and operator
> overloading is a C++ feature, so adding that would prevent
> pthreads-win32 from compiling with C apps.
>
> One alternative is to make a custom comparator type and use that in the
> map declaration - or you could even simply move those operator overloads
> to your own units (they don't have to be defined where the type being
> compared is declared, as long as they've visible at the point where
> they're used - ie. your map declaration).
>
> But bear in mind that in any case, making use of the ptw32_handle_t type
> makes your code nonportable, and since portability is generally the
> reason one is using pthreads-win32 in the first place, this is perhaps
> not the best design for general use.
>
> Will
>
>
> Paolo Brandoli wrote:
> > I have a source code that uses the pthread_t as a key in a std::map.
> > Because pthread-win32 defines pthread_t as a structure, the
> > compilation fails.
> >
> > I added the following lines in my pthread.h header in order to allow
> > the usage of pthread_t in the map:
> >
> > bool operator < (const ptw32_handle_t& left, const ptw32_handle_t& right)
> > {
> >    return left.p < right.p;
> > }
> >
> > bool operator > (const ptw32_handle_t& left, const ptw32_handle_t& right)
> > {
> >    return left.p > right.p;
> > }
> >
> > Bye
> > Paolo Brandoli
> > http://www.puntoexe.com
> >
>
>
> --
> Will Bryant
>
>
>
>
Reply | Threaded
Open this post in threaded view
|

RE: Using pthread_t as a key in a map

Robert Kindred
I have gotten a lot of my tricks from a book which has the acronym of POSA2.
This stands for "Pattern-Oriented Software Architecture" Volume 2, by
Douglas Schmidt.  It is a book about concurrent and network programming.
This is the book that explains a lot of the design of ACE (Adaptive
Communiations Environment).  However, I do not use ACE.

Robert Kindred

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]]On Behalf Of Paolo Brandoli
> Sent: Monday, May 15, 2006 6:57 AM
> To: [hidden email]
> Subject: Re: Using pthread_t as a key in a map
>
>
> Hi Will,
>
> What I'm trying to do is to order the pthread_t pointers so I can
> simulate the windows function "WaitForMultipleObjects"; I have to
> order the pthread_t in a consistent way before attempting to lock
> several mutexes at once.
>
> The way the pthread_t is defined in the library doesn't allow to use
> the < and > operators; those operators can be used when pthread_t is
> defined as a pointer (like in the pthreads implementation on posix
> systems) and not as a structure containing a pointer (as in
> win32-pthread).
>
> I defined the operator for ptw32_handle_t, but it works for pthread_t
> (since it is a synonim for ptw32_handle_t).
>
> Anyway your considerations are right since this breaks the compilation
> on C compilers. On C++ compilers it just remove the errors when I try
> to compare two pthread_t values.
>
> I'm trying to find a more elegant solution, but I'm just staring at
> the monitor and nothing pops up in my brain.
>
> Paolo Brandoli
>
> On 5/15/06, Will Bryant <[hidden email]> wrote:
> > Hi Paolo,
> >
> > Bear in mind that pthreads-win32 is written in C, and operator
> > overloading is a C++ feature, so adding that would prevent
> > pthreads-win32 from compiling with C apps.
> >
> > One alternative is to make a custom comparator type and use that in the
> > map declaration - or you could even simply move those operator overloads
> > to your own units (they don't have to be defined where the type being
> > compared is declared, as long as they've visible at the point where
> > they're used - ie. your map declaration).
> >
> > But bear in mind that in any case, making use of the ptw32_handle_t type
> > makes your code nonportable, and since portability is generally the
> > reason one is using pthreads-win32 in the first place, this is perhaps
> > not the best design for general use.
> >
> > Will
> >
> >
> > Paolo Brandoli wrote:
> > > I have a source code that uses the pthread_t as a key in a std::map.
> > > Because pthread-win32 defines pthread_t as a structure, the
> > > compilation fails.
> > >
> > > I added the following lines in my pthread.h header in order to allow
> > > the usage of pthread_t in the map:
> > >
> > > bool operator < (const ptw32_handle_t& left, const
> ptw32_handle_t& right)
> > > {
> > >    return left.p < right.p;
> > > }
> > >
> > > bool operator > (const ptw32_handle_t& left, const
> ptw32_handle_t& right)
> > > {
> > >    return left.p > right.p;
> > > }
> > >
> > > Bye
> > > Paolo Brandoli
> > > http://www.puntoexe.com
> > >
> >
> >
> > --
> > Will Bryant
> >
> >
> >
> >
>

Reply | Threaded
Open this post in threaded view
|

Re: Using pthread_t as a key in a map

Ross Johnson-3
In reply to this post by Will Bryant-2
A reasonably portable solution to this came up the other day (privately)
in relation to using pthreads-win32 pthread_t with openssl. It is the
following:

    #define PT(t) (*((unsigned long *)&(t)))
    pthread_t thrA, thrB;
    ...
    PT(thrA)  <  PT(thrB)

etc.

Although this still relies on the pointer component being at offset 0
inside the pthread_t struct (which was made this way deliberately so
probably won't change in the future), it does avoid having to explicitly
use or know about ptw32_handle_t. You still lose the handle uniqueness
"guarantee" that the pthread_t struct provides though, so that you then
need to take extra care that the threads that you do this with don't
detach without you realising it.

By the way, the pthread_t in pthreads-win32 is POSIX compliant. POSIX
doesn't require pthread_t to be a scalar type, and in fact all but
requires that POSIX compliant applications not presume the type of
pthread_t.

Ross

Will Bryant wrote:

>Hi Paolo,
>
>Bear in mind that pthreads-win32 is written in C, and operator
>overloading is a C++ feature, so adding that would prevent
>pthreads-win32 from compiling with C apps.
>
>One alternative is to make a custom comparator type and use that in the
>map declaration - or you could even simply move those operator overloads
>to your own units (they don't have to be defined where the type being
>compared is declared, as long as they've visible at the point where
>they're used - ie. your map declaration).
>
>But bear in mind that in any case, making use of the ptw32_handle_t type
>makes your code nonportable, and since portability is generally the
>reason one is using pthreads-win32 in the first place, this is perhaps
>not the best design for general use.
>
>Will
>
>
>Paolo Brandoli wrote:
>  
>
>>I have a source code that uses the pthread_t as a key in a std::map.
>>Because pthread-win32 defines pthread_t as a structure, the
>>compilation fails.
>>
>>I added the following lines in my pthread.h header in order to allow
>>the usage of pthread_t in the map:
>>
>>bool operator < (const ptw32_handle_t& left, const ptw32_handle_t& right)
>>{
>>   return left.p < right.p;
>>}
>>
>>bool operator > (const ptw32_handle_t& left, const ptw32_handle_t& right)
>>{
>>   return left.p > right.p;
>>}
>>
>>Bye
>>Paolo Brandoli
>>http://www.puntoexe.com
>>
>>    
>>
>
>
>  
>

Reply | Threaded
Open this post in threaded view
|

Re: Using pthread_t as a key in a map

Ross Johnson-3
Paolo,

In your original message you said you were trying to create
functionality similar to WaitForMultipleObjects(). In pthreads this is
usually done using condition variables. I.e. similar to the way that
WaitForMultipleObjects() returns the array index of the handle that
caused it to return, or an error. The signaling thread will set the
condition variable directly and the signaled (waiting) thread will check
the condition variable directly.

Re using pthread_t as a map key, the only compare operation that you can
legally do on pthread_t is test for equality via pthread_equal().

Ross

Ross Johnson wrote:

> A reasonably portable solution to this came up the other day
> (privately) in relation to using pthreads-win32 pthread_t with
> openssl. It is the following:
>
>    #define PT(t) (*((unsigned long *)&(t)))
>    pthread_t thrA, thrB;
>    ...
>    PT(thrA)  <  PT(thrB)
>
> etc.
>
> Although this still relies on the pointer component being at offset 0
> inside the pthread_t struct (which was made this way deliberately so
> probably won't change in the future), it does avoid having to
> explicitly use or know about ptw32_handle_t. You still lose the handle
> uniqueness "guarantee" that the pthread_t struct provides though, so
> that you then need to take extra care that the threads that you do
> this with don't detach without you realising it.
>
> By the way, the pthread_t in pthreads-win32 is POSIX compliant. POSIX
> doesn't require pthread_t to be a scalar type, and in fact all but
> requires that POSIX compliant applications not presume the type of
> pthread_t.
>
> Ross
>
> Will Bryant wrote:
>
>> Hi Paolo,
>>
>> Bear in mind that pthreads-win32 is written in C, and operator
>> overloading is a C++ feature, so adding that would prevent
>> pthreads-win32 from compiling with C apps.
>>
>> One alternative is to make a custom comparator type and use that in the
>> map declaration - or you could even simply move those operator overloads
>> to your own units (they don't have to be defined where the type being
>> compared is declared, as long as they've visible at the point where
>> they're used - ie. your map declaration).
>>
>> But bear in mind that in any case, making use of the ptw32_handle_t type
>> makes your code nonportable, and since portability is generally the
>> reason one is using pthreads-win32 in the first place, this is perhaps
>> not the best design for general use.
>>
>> Will
>>
>>
>> Paolo Brandoli wrote:
>>  
>>
>>> I have a source code that uses the pthread_t as a key in a std::map.
>>> Because pthread-win32 defines pthread_t as a structure, the
>>> compilation fails.
>>>
>>> I added the following lines in my pthread.h header in order to allow
>>> the usage of pthread_t in the map:
>>>
>>> bool operator < (const ptw32_handle_t& left, const ptw32_handle_t&
>>> right)
>>> {
>>>   return left.p < right.p;
>>> }
>>>
>>> bool operator > (const ptw32_handle_t& left, const ptw32_handle_t&
>>> right)
>>> {
>>>   return left.p > right.p;
>>> }
>>>
>>> Bye
>>> Paolo Brandoli
>>> http://www.puntoexe.com
>>>
>>>  
>>
>>
>>
>>  
>>
>

Reply | Threaded
Open this post in threaded view
|

Re: Using pthread_t as a key in a map

Paolo Brandoli
Thank you very much for your suggestions.
I'm going to rewrite the WaitForMultipleObjects-like function.

The function should wait until all the mutexes are available, but
should NOT keep
 some of them locked (some cpu cycles are ok) until all of them become
available.

The code I wrote was based on an example from the IBM website (I think
it was for the 360 series? I really don't remember...).

I think that I will take this approach to order the mutexes I will
include the pthread_t in a structure that contains a scalar unique ID.

I will let you know how this task proceeds.

Paolo

On 5/16/06, Ross Johnson <[hidden email]> wrote:

> Paolo,
>
> In your original message you said you were trying to create
> functionality similar to WaitForMultipleObjects(). In pthreads this is
> usually done using condition variables. I.e. similar to the way that
> WaitForMultipleObjects() returns the array index of the handle that
> caused it to return, or an error. The signaling thread will set the
> condition variable directly and the signaled (waiting) thread will check
> the condition variable directly.
>
> Re using pthread_t as a map key, the only compare operation that you can
> legally do on pthread_t is test for equality via pthread_equal().
>
> Ross
>
> Ross Johnson wrote:
>
> > A reasonably portable solution to this came up the other day
> > (privately) in relation to using pthreads-win32 pthread_t with
> > openssl. It is the following:
> >
> >    #define PT(t) (*((unsigned long *)&(t)))
> >    pthread_t thrA, thrB;
> >    ...
> >    PT(thrA)  <  PT(thrB)
> >
> > etc.
> >
> > Although this still relies on the pointer component being at offset 0
> > inside the pthread_t struct (which was made this way deliberately so
> > probably won't change in the future), it does avoid having to
> > explicitly use or know about ptw32_handle_t. You still lose the handle
> > uniqueness "guarantee" that the pthread_t struct provides though, so
> > that you then need to take extra care that the threads that you do
> > this with don't detach without you realising it.
> >
> > By the way, the pthread_t in pthreads-win32 is POSIX compliant. POSIX
> > doesn't require pthread_t to be a scalar type, and in fact all but
> > requires that POSIX compliant applications not presume the type of
> > pthread_t.
> >
> > Ross
> >
> > Will Bryant wrote:
> >
> >> Hi Paolo,
> >>
> >> Bear in mind that pthreads-win32 is written in C, and operator
> >> overloading is a C++ feature, so adding that would prevent
> >> pthreads-win32 from compiling with C apps.
> >>
> >> One alternative is to make a custom comparator type and use that in the
> >> map declaration - or you could even simply move those operator overloads
> >> to your own units (they don't have to be defined where the type being
> >> compared is declared, as long as they've visible at the point where
> >> they're used - ie. your map declaration).
> >>
> >> But bear in mind that in any case, making use of the ptw32_handle_t type
> >> makes your code nonportable, and since portability is generally the
> >> reason one is using pthreads-win32 in the first place, this is perhaps
> >> not the best design for general use.
> >>
> >> Will
> >>
> >>
> >> Paolo Brandoli wrote:
> >>
> >>
> >>> I have a source code that uses the pthread_t as a key in a std::map.
> >>> Because pthread-win32 defines pthread_t as a structure, the
> >>> compilation fails.
> >>>
> >>> I added the following lines in my pthread.h header in order to allow
> >>> the usage of pthread_t in the map:
> >>>
> >>> bool operator < (const ptw32_handle_t& left, const ptw32_handle_t&
> >>> right)
> >>> {
> >>>   return left.p < right.p;
> >>> }
> >>>
> >>> bool operator > (const ptw32_handle_t& left, const ptw32_handle_t&
> >>> right)
> >>> {
> >>>   return left.p > right.p;
> >>> }
> >>>
> >>> Bye
> >>> Paolo Brandoli
> >>> http://www.puntoexe.com
> >>>
> >>>
> >>
> >>
> >>
> >>
> >>
> >
>
>