http://d.puremagic.com/issues/show_bug.cgi?id=10740

           Summary: std.concurrency send() fails with structs over 32
                    bytes
           Product: D
           Version: D2
          Platform: x86_64
        OS/Version: Linux
            Status: NEW
          Severity: major
          Priority: P2
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: david@eagen.com


--- Comment #0 from David Eagen <david@eagen.com> 2013-07-31 21:44:11 PDT ---
Using 2.063.2 and 2.064-devel-333c6dd:

import std.concurrency : receiveOnly, send, thisTid;
import std.exception : assumeUnique;
import std.variant;

struct JustRight
{
    byte[32] j;
}

struct TooBig
{
    byte[33] t;
}

void main()
{
    JustRight[1] jArray;
    TooBig[1]    tArray;

    Variant vj = jArray[];
    Variant vt = tArray[];

    thisTid.send(vj);
    thisTid.send(vt);

    thisTid.send(assumeUnique(jArray[]));
    //thisTid.send(assumeUnique(tArray[])); // Fails to compile

    auto received = receiveOnly!((JustRight)[]);
}

If the send of tArray is commented out the compilation fails with:

src/phobos/std/variant.d(558): Error: cannot modify immutable expression *p

So, 32-byte structs can be sent (as arrays) using send or if you first wrap it in an Variant object. Greater than 32-byte structs can be sent ONLY if they are pre-wrapped in a Variant. The size of the data shouldn't limit it from being sent using send().

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--- Comment #1 from David Eagen <david@eagen.com> 2013-08-01 04:33:47 PDT ---
Should have said:

"If the send of tArray is uncommented the compilation fails with:"

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Johannes Pfau <johannespfau@gmail.com> changed:

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


--- Comment #2 from Johannes Pfau <johannespfau@gmail.com> 2013-08-24 06:08:34 PDT ---
There recently was a bug report for GDC/ARM regarding this. As variants max size is determined by creal which is only 16 bytes on most non-x86 architectures this error already happens with structs > 16 bytes on these architectures.

Another test case with different error message:
---------
struct Big
{
    int[10] a;
}

import std.concurrency, std.variant, core.thread;

void loop()
{
    while(true)
    {
        Thread.sleep(seconds(10));
    }
}

void main()
{
    auto x = spawn(&loop);
    x.send(Big());
}
---------
http://dpaste.dzfl.pl/f103dbac

core.exception.AssertError@/opt/compilers/dmd2/include/std/variant.d(280):
target must be non-null

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