digitalmars.D.bugs - [Issue 1382] New: memory allocated for arrays in CTFE functions during compilation is not released
- d-bugmail puremagic.com Jul 27 2007
- d-bugmail puremagic.com Apr 29 2008
- d-bugmail puremagic.com Jul 21 2008
- d-bugmail puremagic.com Dec 02 2008
- d-bugmail puremagic.com Aug 03 2009
- d-bugmail puremagic.com Aug 31 2009
- d-bugmail puremagic.com Jun 04 2010
- d-bugmail puremagic.com Dec 06 2010
http://d.puremagic.com/issues/show_bug.cgi?id=1382 Summary: memory allocated for arrays in CTFE functions during compilation is not released Product: D Version: 1.019 Platform: PC OS/Version: Linux Status: NEW Severity: normal Priority: P2 Component: DMD AssignedTo: bugzilla digitalmars.com ReportedBy: kamm-removethis incasoftware.de This problem is encountered when large arrays are manipulated during CTFE. Symtoms are dmd allocating a lot of memory, eating up all swap and finally terminating with an out of memory error. The core of the problem can be seen in this code -- char[] make_empty_string(int n) { char[] result; for(int i = 0; i < n; ++i) result ~= " "; return result; } const char[] largestring = make_empty_string(100000); void main() {} --- This snippet will require 5 gb of memory to compile instead of the mere 100 kb the final string will require. It is caused by the intermediate strings stored in result during the iteration never being discarded. The problem is not limited to concatenation, modifications of a single element of the array will also cause the whole array to be duplicated. While this particular piece of code can be rewritten to consume less memory, that's not generally possible. An example where reduction is not possible is splitting a string into substrings. It does come up in practice: Someone wanted to generate a function to get the Unicode general catergory for a dchar from the textfiles from the Unicode Character Database and ran into this issue. I wanted to parse the D BNF to generate a parser at compile time and had dmd exit with an out of memory error. It seems CTFE needs a compile time garbage collector. --
Jul 27 2007
d-bugmail puremagic.com http://d.puremagic.com/issues/show_bug.cgi?id=1382 clugdbug yahoo.com.au changed: What |Removed |Added ---------------------------------------------------------------------------- Severity|normal |blocker ------- Comment #1 from clugdbug yahoo.com.au 2008-04-29 05:30 ------- I'm raising the severity of this to blocker, since it makes CTFE metaprogramming libraries unusable in practice. Fortunately development of such libraries is still possible, although both BCS and I are experiencing some horrific compilation times, even after inserting workarounds where possible. We are having to reduce the complexity of our test code. --
Apr 29 2008
http://d.puremagic.com/issues/show_bug.cgi?id=1382 ------- Comment #2 from kamm-removethis incasoftware.de 2008-07-22 00:52 ------- Has DMD stopped using boehm-gc? If I try this very example on LLVMDC (which does use boehm-gc), memory usage never exceeds a certain level (< 1 MB). So maybe re-enabling the garbage collector for DMD will fix all CTFE related memory issues? --
Jul 21 2008
http://d.puremagic.com/issues/show_bug.cgi?id=1382 ------- Comment #3 from kamm-removethis incasoftware.de 2008-12-02 12:31 ------- We've had some success with reenabling boehm-gc: http://www.dsource.org/projects/ldc/ticket/49 . "Another test with USE_BOEHM_GC=0, REDIRECT_MALLOC=GC_malloc and IGNORE_FREE seemed to yield good results, with no segfaults and collecting CTFE memory properly." --
Dec 02 2008
http://d.puremagic.com/issues/show_bug.cgi?id=1382 Don <clugdbug yahoo.com.au> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |clugdbug yahoo.com.au --- Comment #4 from Don <clugdbug yahoo.com.au> 2009-08-03 05:18:25 PDT --- I don't think Boehm gc is the answer. Note that this is very closely related to bug#1330. I think the CTFE implementation of arrays needs (a) reference semantics and (b) reference counting. Here's an example of a terrible case, which allocates several Gb of RAM: int junk(int n) { int[] result = new int[10000]; for(int i = 0; i < n; ++i) { result[0]= i; } return 0; } const int bad = junk(100000); void main() {} This particular case could be solved by adding a reference-based system for storing array values, instead of doing copy-on-write -- and that's required for bug #1330 anyway. Once that's in place, the array values could be allocated in a controlled manner (eg, retain a list of all allocated CTFE arrays). A dedicated precise GC can then be simple and fast, since it only needs to check for array references in the current function, and they can only be in the local variables which are arrays or structs. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Aug 03 2009
http://d.puremagic.com/issues/show_bug.cgi?id=1382 Don <clugdbug yahoo.com.au> changed: What |Removed |Added ---------------------------------------------------------------------------- Severity|blocker |critical --- Comment #5 from Don <clugdbug yahoo.com.au> 2009-08-31 23:59:27 PDT --- Reducing severity back to critical, since the voting system takes care of the importance. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Aug 31 2009
http://d.puremagic.com/issues/show_bug.cgi?id=1382 bearophile_hugs eml.cc changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |bearophile_hugs eml.cc --- Comment #6 from bearophile_hugs eml.cc 2010-06-04 15:19:11 PDT --- A partially artificial test case. Faster and better versions are quite possible, but I expect dmd to be able to run this quickly. import std.stdio: writeln; ubyte[1 << NPOW] setBits(int NPOW)() { nothrow pure uint setBits8(uint n) { uint result; foreach (i; 0 .. 8) if (n & (1 << i)) result++; return result; } nothrow pure uint setBits16(uint n) { enum uint FIRST_UBYTE = 0b0000_0000_1111_1111; enum uint SECOND_UBYTE = 0b1111_1111_0000_0000; return setBits8(n & FIRST_UBYTE) + setBits8((n & SECOND_UBYTE) >> 8); } typeof(return) result; foreach (i; 1 .. result.length) result[i] = cast(typeof(result[0]))setBits16(i); return result; } enum nbits = setBits!16(); // currently 12 is about the max void main() { writeln(nbits); } -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Jun 04 2010
http://d.puremagic.com/issues/show_bug.cgi?id=1382 Rob Jacques <sandford jhu.edu> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |sandford jhu.edu --- Comment #7 from Rob Jacques <sandford jhu.edu> 2010-12-06 12:09:04 PST --- I just came across this bug while working on improving std.variant: the combination of templates + ctfe + unittests resulted in out of memory errors. I've also traced down another issue (I don't know if it should be filed separately or not): It appears that _any_ access of an array variable allocates ram, resulting in drastically slower compile times (+55 seconds) and excess memory usage (30+ mb in this case using DMD 2.050) string ctfeTest() { char[] result; result.length = ushort.max; char c; for(size_t i = 0; i < result.length; i++) {} // Allocates for(size_t i = 0; i < ushort.max; i++) {} // Doesn't allocate for(size_t i = 0; i < ushort.max; i++) { // Allocates c = result[i]; } for(size_t i = 0; i < ushort.max; i++) { // Doesn't allocate c = cast(ubyte)('A' + i%26); } return cast(string)result; } -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Dec 06 2010