• Manu (44/44) Oct 06 2018 So I'm working on a SMT infrastructure, and expression of
• Nicholas Wilson (31/79) Oct 06 2018 A delta comparison with shared
• Manu (37/44) Oct 06 2018 Right, that's kinda what I want to model... but the more I think of
• Stefan Koch (20/71) Oct 08 2018 I think it should be more like this
• Kagamin (10/10) Oct 10 2018 struct Bob

Manu <turkeyman gmail.com> writes:

So I'm working on a SMT infrastructure, and expression of
thread-safety is a core design mechanic... but I'm really struggling
to express it in terms of the type system.
I figure I'll throw some design challenges out here and see if anyone
can offer some good ideas.

The thing I'm trying to model is an attribute along the lines of
`shared`, but actually useful ;)
I'll use the attribute `threadsafe` in place of `shared`, and see
where that goes.

Consider:
struct Bob
{
  int x;
  threadsafe Atomic!int y;

  void m1();
  void m2() threadsafe;;

  void overloaded();
  void overloaded() threadsafe;
}

void func(Bob x, threadsafe Bob y)
{
  x.x = 10; // fine
  x.y = 10; // fine
  x.m1(); // fine
  x.m2(); // fine
  x.overloaded(); // fine, use the un-threadsafe overload

  y.x = 10; // ERROR, a threadsafe reference can NOT modify an
un-threadsafe member
  y.y = 10; // fine
  x.m1(); // ERROR, method not threadsafe
  x.m2(); // fine
  x.overloaded(); // fine, use the threadsafe overload

  threadsafe Bob* p = &x; // can take threadsafe reference to
thread-local object
}

This is loosely what `shared` models, but there's a few differences:
1. thread-local can NOT promote to shared
2. shared `this` applies to members

For `shared` to be useful, it should be that a shared reference to
something inhibits access to it's thread-local stuff. And in that
world, then I believe that thread-local promotion to shared would work
like const does.

I guess I'm wondering; should `shared` be transitive? Perhaps that's
what's wrong with it...?

Nicholas Wilson <iamthewilsonator hotmail.com> writes:

On Sunday, 7 October 2018 at 01:59:21 UTC, Manu wrote:
 So I'm working on a SMT infrastructure, and expression of
 thread-safety is a core design mechanic... but I'm really 
 struggling
 to express it in terms of the type system.
 I figure I'll throw some design challenges out here and see if 
 anyone
 can offer some good ideas.

 The thing I'm trying to model is an attribute along the lines of
 `shared`, but actually useful ;)
 I'll use the attribute `threadsafe` in place of `shared`, and 
 see
 where that goes.

 Consider:
 struct Bob
 {
   int x;
   threadsafe Atomic!int y;

   void m1();
   void m2() threadsafe;;

   void overloaded();
   void overloaded() threadsafe;
 }

 void func( ref Bob x, ref threadsafe Bob y)
 {
   x.x = 10; // fine
   x.y = 10; // fine
   x.m1(); // fine
   x.m2(); // fine
   x.overloaded(); // fine, use the un-threadsafe overload

   y.x = 10; // ERROR, a threadsafe reference can NOT modify an
 un-threadsafe member
   y.y = 10; // fine
   x.m1(); // ERROR, method not threadsafe
   x.m2(); // fine
   x.overloaded(); // fine, use the threadsafe overload

   threadsafe Bob* p = &x; // can take threadsafe reference to
 thread-local object
 }

 This is loosely what `shared` models, but there's a few 
 differences:
 1. thread-local can NOT promote to shared
 2. shared `this` applies to members

 For `shared` to be useful, it should be that a shared reference 
 to something inhibits access to it's thread-local stuff. And in 
 that world, then I believe that thread-local promotion to 
 shared would work like const does.

 I guess I'm wondering; should `shared` be transitive? Perhaps 
 that's what's wrong with it...?

A delta comparison with shared

void func( ref Bob x, ref threadshared /* either shared or 
threadsafe*/ Bob y)
{
  // threadsafe / shared
   x.x = 10; // fine / fine
   x.y = 10; // fine / fine uses atomics
   x.m1(); // fine / fine
   x.m2(); // fine / error cannot call shared method on unshared 
object
   x.overloaded(); // fine, use the un-threadsafe overload / fine

   y.x = 10; // ERROR, a threadsafe reference can NOT modify an 
un-threadsafe member / error
   y.y = 10; // fine / fine (using atomics)
// Assuming these are supposed to be y not x
   y.m1(); // ERROR, method not threadsafe / error
   y.m2(); // fine / fine
   y.overloaded(); // fine, use the threadsafe overload / fine

   threadsafe Bob* p = &x; // can take threadsafe reference to 
thread-local object / error
}

Differences:
Can call threadsafe method on thread local / unshared
Can take threadsafe reference to thread-local object.

One thing that occurred to me is that _objects_ are shared, 
whereas _functions/methods_ (and their parameters) are thread 
safe .

Theadsafe is kind of like a const (as to mutable/immutable) to 
threading, a promise to behave correctly in the presence of 
threading. thread safe references therefore must not escape.

Manu <turkeyman gmail.com> writes:

On Sat, Oct 6, 2018 at 7:40 PM Nicholas Wilson via Digitalmars-d
<digitalmars-d puremagic.com> wrote:
 [...]

 One thing that occurred to me is that _objects_ are shared,
 whereas _functions/methods_ (and their parameters) are thread
 safe .

 Theadsafe is kind of like a const (as to mutable/immutable) to
 threading, a promise to behave correctly in the presence of
 threading. thread safe references therefore must not escape.

Right, that's kinda what I want to model... but the more I think of
it, the more I think that experience can fit into `shared`, because
it's almost there, and the current incarnation of shared is
objectively useless.

Consider shared as is today;
struct Bob
{
  int x;
  void f() shared
  {
    x = 10; // <- this compiles... WAT?!
  }
}

Right now, if you have a shared instance, you can read/write to the
members... and that makes *absolutely no sense* no matter how you look
at it.
There is no reality where you have a shared thing, and accessing
members un-controlled can be safe.

Conventional wisdom is that when you have a shared thing, and you want
to do stuff with it, you must acquire locks (or whatever) and case
shared away. That should apply to f() above.

struct Bob
{
  int x;
  void f() shared
  {
    auto lock = getLock();
    auto unshared = shared_cast(&this);
    unshared.x = 10; // <- this is now okay.
  }
}

If we made a change were `shared` lost the ability to access
non-`shared` members, I don't think that would interfere with current
or proposed uses of shared in any way whatsoever... and we would make
shared useful in the process.

Stefan Koch <uplink.coder googlemail.com> writes:

On Sunday, 7 October 2018 at 02:59:12 UTC, Manu wrote:
 On Sat, Oct 6, 2018 at 7:40 PM Nicholas Wilson via 
 Digitalmars-d <digitalmars-d puremagic.com> wrote:
 [...]

 One thing that occurred to me is that _objects_ are shared, 
 whereas _functions/methods_ (and their parameters) are thread 
 safe .

 Theadsafe is kind of like a const (as to mutable/immutable) to 
 threading, a promise to behave correctly in the presence of 
 threading. thread safe references therefore must not escape.

 Right, that's kinda what I want to model... but the more I 
 think of it, the more I think that experience can fit into 
 `shared`, because it's almost there, and the current 
 incarnation of shared is objectively useless.

 Consider shared as is today;
 struct Bob
 {
   int x;
   void f() shared
   {
     x = 10; // <- this compiles... WAT?!
   }
 }

 Right now, if you have a shared instance, you can read/write to 
 the
 members... and that makes *absolutely no sense* no matter how 
 you look
 at it.
 There is no reality where you have a shared thing, and accessing
 members un-controlled can be safe.

 Conventional wisdom is that when you have a shared thing, and 
 you want
 to do stuff with it, you must acquire locks (or whatever) and 
 case
 shared away. That should apply to f() above.

 struct Bob
 {
   int x;
   void f() shared
   {
     auto lock = getLock();
     auto unshared = shared_cast(&this);
     unshared.x = 10; // <- this is now okay.
   }
 }

 If we made a change were `shared` lost the ability to access 
 non-`shared` members, I don't think that would interfere with 
 current or proposed uses of shared in any way whatsoever... and 
 we would make shared useful in the process.

I think it should be more like this
shared struct Bob
{
     shared int x;
     void f() shared
     {
       Laquire:
       auto owned_bob = try_aquire(&this, pthread_self());
       // type will be the same as Bob* but without shared 
stripped from variables
       // and without any functions
       if (owned_bob is null)
       {
           __mmPause();
           goto Laquire;
       }
       *owned_bob.x = 10;
     }

}

Kagamin <spam here.lot> writes:

struct Bob
{
   threadsafe Atomic!(string[string]) y;
}

void f(ref threadsafe Bob b)
{
   string[string] aa=b.y;
   aa["b"]="c";
}

Like this?