November 01, 2010
Hello.  I'm new to D. It's been a long time since I've coded anything with classes.  Please excuse my ignorance.

Here's a very simplified version of what I'm trying to do:

import std.c.linux.linux;
import std.stdio;
class FOO
    {
    this()
        {
        sa.sa_handler = &handler;
        sigemptyset(&sa.sa_mask);
        sa.sa_flags = SA_RESTART;
        sigaction(SIGALRM, &sa, null);
        }

    ~this()
        {
        sa.sa_handler = SIG_DFL;
        sigemptyset(&sa.sa_mask);
        sa.sa_flags = SA_RESTART;
        sigaction(SIGALRM, &sa, null);
        }

    private:
    sigaction_t sa;

    void handler(int signal)
        {
        writeln("Got an alarm signal.");
        }
    }


Is there a way to do it without removing handler() from the class?  When I try
compiling, I get: Error: cannot implicitly convert expression (&this.handler)
of type void delegate(int signal) to void C function(int).

Thank you,
- Peter
November 01, 2010
On Mon, 01 Nov 2010 05:27:06 +0300, Peter Federighi <pfederighi@yahoo.com> wrote:

> Hello.  I'm new to D. It's been a long time since I've coded anything with
> classes.  Please excuse my ignorance.
>
> Here's a very simplified version of what I'm trying to do:
>
> import std.c.linux.linux;
> import std.stdio;
> class FOO
>     {
>     this()
>         {
>         sa.sa_handler = &handler;
>         sigemptyset(&sa.sa_mask);
>         sa.sa_flags = SA_RESTART;
>         sigaction(SIGALRM, &sa, null);
>         }
>
>     ~this()
>         {
>         sa.sa_handler = SIG_DFL;
>         sigemptyset(&sa.sa_mask);
>         sa.sa_flags = SA_RESTART;
>         sigaction(SIGALRM, &sa, null);
>         }
>
>     private:
>     sigaction_t sa;
>
>     void handler(int signal)
>         {
>         writeln("Got an alarm signal.");
>         }
>     }
>
>
> Is there a way to do it without removing handler() from the class?  When I try
> compiling, I get: Error: cannot implicitly convert expression (&this.handler)
> of type void delegate(int signal) to void C function(int).
>
> Thank you,
> - Peter

No, unfortunately not. A delegate is a function pointer PLUS 'this'. The C API you are using allows providing function only, without a context. As such, you need to store 'this' pointer somewhere else. It is usually done by means of of a special userData variable which is additionally passed to the callback (looks like we are out of luck this time), or storing it in a global variable:

Foo foo;
void externalHandler(int signal)
{
    assert(foo !is null);
    foo.handler(signal);
}

class Foo
{
    this() {
        assert(foo is null);
        foo = this;
        sa.sa_handler = &externalHandler;
        // ...
    }
    ~this() {
        assert(foo is this);
        foo = null;
        // ...
    }
    // ...
}
November 01, 2010
"Peter Federighi" <pfederighi@yahoo.com> wrote in message news:ial8hq$2137$1@digitalmars.com...
> Is there a way to do it without removing handler() from the class?  When I
> try
> compiling, I get: Error: cannot implicitly convert expression
> (&this.handler)
> of type void delegate(int signal) to void C function(int).

Yes, but it requires some nasty code.

(Not tested on anything except windows)
http://yebblies.com/thunk.d

(Also not tested)

import yebblies.thunk.d;
import std.c.linux.linux;
import std.stdio;
class FOO
    {
    this()
        {
        th = thunk!"C"(&handler);
        sa.sa_handler = th.ptr;
        sigemptyset(&sa.sa_mask);
        sa.sa_flags = SA_RESTART;
        sigaction(SIGALRM, &sa, null);
        }

    ~this()
        {
        sa.sa_handler = SIG_DFL;
        sigemptyset(&sa.sa_mask);
        sa.sa_flags = SA_RESTART;
        sigaction(SIGALRM, &sa, null);
        }

    private:
    sigaction_t sa;
    typeof(thunk!"C"(&handler)) th;

    void handler(int signal)
        {
        writeln("Got an alarm signal.");
        }
    }

It basically gets around the restriction by writing some code into memory that passes the delegate params in unused registers.  I don't even know if the page allocation code works on anything except windows.

Daniel


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