http://d.puremagic.com/issues/show_bug.cgi?id=9704

           Summary: Destructor not called on function calls if postblit
                    throws
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: johannespfau@gmail.com


--- Comment #0 from Johannes Pfau <johannespfau@gmail.com> 2013-03-12 11:35:39 PDT ---
See the attached testcase:

If the throw statement in B's postblit is commented we see the expected result:
A:this(this)
B:this(this)
A:~this
B:~this
B:~this
A:~this

The function call creates two copies, then the destructors are called for the
originals and for the copies. But if the throw statement is in place:
A:this(this)
B:this(this)
B:~this
A:~this
object.Exception@test99.d(12): Boom

We see that the destructors for the copies are not called. It can be argued that this is valid for the B copy, as it's postblit threw.

But for the copy of A the destructor must be called as the postblit was called and succeeded.


The problem is that the destructors are currently called in the callee but the postblits in the caller. If an exception is thrown in between those calls, the destructor can't be called.

A possible solution is to move the destructor to the caller. But in this case the parameter (the copy) must be passed by invisible reference so that the destructor actually sees the updated value after the callee returns.

(Note that it might be useful to make an exception for non-PODs without destructors here. Those shouldn't be affected by this issue and could be treated like PODs when being passed to a function as an optimization.)

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--- Comment #1 from Johannes Pfau <johannespfau@gmail.com> 2013-03-12 11:36:29 PDT ---
Created an attachment (id=1201)
test case

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Maxim Fomin <maxim@maxim-fomin.ru> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |maxim@maxim-fomin.ru


--- Comment #2 from Maxim Fomin <maxim@maxim-fomin.ru> 2013-03-12 13:13:41 PDT ---
(In reply to comment #0)
> The problem is that the destructors are currently called in the callee but the postblits in the caller. If an exception is thrown in between those calls, the destructor can't be called.

To be more precise, it happens during evaluation of function argument which follows some struct argument and throws exception.

extern(C) int printf(const char* fmt, ...);

struct A
{
    this(this) { printf("A:this(this)\n");}
    ~this() { printf("A:~this\n"); }
    uint data;
}

int foo() { throw new Exception(""); }


void func(A a, int i) {}

void main()
{
    A a;
    func(a, foo());
}

Here should be two destructors: for "a" and " __cpcttmpXXX" structs. And calling dtor is unavoidable since postblit may deep copy some memory.

> A possible solution is to move the destructor to the caller. But in this case the parameter (the copy) must be passed by invisible reference so that the destructor actually sees the updated value after the callee returns.
> 
> (Note that it might be useful to make an exception for non-PODs without destructors here. Those shouldn't be affected by this issue and could be treated like PODs when being passed to a function as an optimization.)

Alternatively a copy operation can be moved into callee or D runtime can be boosted to cope with such problem.

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monarchdodra@gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |andrei@erdani.com


--- Comment #3 from monarchdodra@gmail.com 2013-07-12 11:05:06 PDT ---
*** Issue 10623 has been marked as a duplicate of this issue. ***

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monarchdodra@gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |monarchdodra@gmail.com


--- Comment #4 from monarchdodra@gmail.com 2013-07-12 11:07:53 PDT ---
(In reply to comment #3)
> *** Issue 10623 has been marked as a duplicate of this issue. ***

For reference, this was also discussed in learn. http://forum.dlang.org/group/digitalmars.D.learn

http://forum.dlang.org/thread/20130628005448.00000969@unknown

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--- Comment #5 from Andrei Alexandrescu <andrei@erdani.com> 2013-07-12 14:17:12 PDT ---
Pasting the additional example here for reference:

import std.stdio;

struct S1 {
    this(int) { writeln("constructed"); }
    ~this() { writeln("destroyed"); }
}
struct S2 { this(int) { throw new Exception("a"); } }

void fun(S1, S2, S1) {}

void main()
{
    fun(S1(2), S2(2), S1(2));
}

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