[Issue 2306] New: Scope for dynamic arrays should free memory.

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=2306

           Summary: Scope for dynamic arrays should free memory.
           Product: D
           Version: 2.018
          Platform: PC
        OS/Version: Windows
            Status: NEW
          Severity: minor
          Priority: P3
         Component: DMD
        AssignedTo: bugzilla at digitalmars.com
        ReportedBy: dsimcha at yahoo.com


Because of the overhead of frequent garbage collections, as well as false
pointer issues with conservative GC, it is sometimes desirable to use
RAII-style memory management for large arrays.  Most RAII stuff in D is done
using the scope keyword.  However, when applied to dynamic arrays, the scope
keyword apparently does absolutely nothing.  The following program runs out of
memory after 3 iterations due to false pointer issues, as is expected when
allocating a 400 MB array in 4 GB address space w/ conservative GC as the only
method being used to free memory.

import std.stdio;

void main() {
    uint count = 0;
    while(true) {
        test();
        writefln(++count);
    }
}

void test() {
    scope uint[] foo = new uint[100_000_000];
}

However, the following actually runs indefinitely:

import std.stdio;

void main() {
    uint count = 0;
    while(true) {
        test();
        writefln(++count);
    }
}

void test() {
    uint[] foo = new uint[100_000_000];
    scope(exit) delete foo;
}

This isn't a very serious bug, since there's an obvious, simple workaround, but
it's still an inconsistency in the language design, and ideally should be
fixed.


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