digitalmars.D.learn - Segmentation fault on closing file in destructor
- Tom Kazimiers (39/39) Sep 26 2010 Hi,
- Simen kjaeraas (11/18) Sep 26 2010 Likely, it is this[1]:
- Tom Kazimiers (10/20) Sep 26 2010 thanks for your reply. I did not know that the garbage collector works
- bearophile (4/6) Sep 26 2010 Can you use scope(exit) or the std.stdio.File?
- Tom Kazimiers (8/14) Sep 26 2010 Well, I have no idea. You mentioning scope(exit) was actually the first
- Simen kjaeraas (4/15) Sep 26 2010 http://digitalmars.com/d/2.0/statement.html#ScopeGuardStatement
- Tom Kazimiers (7/14) Sep 28 2010 thanks, strange I did not find that page by searching. Good to know
- Lars T. Kyllingstad (24/25) Sep 27 2010 Well, for one thing you won't have to write your code all over again whe...
- =?UTF-8?B?IkrDqXLDtG1lIE0uIEJlcmdlciI=?= (17/38) Sep 26 2010 The way I see it, there are two possible situations:
- Tom Kazimiers (6/19) Sep 28 2010 That are probably the two choices I have, yes. I already have such a
- Steven Schveighoffer (16/35) Sep 27 2010 Then do not use a destructor. There is no way currently for the
- Michel Fortin (18/39) Sep 26 2010 That's it indeed, but I'll add that it's the File struct that is at
- Steven Schveighoffer (5/32) Sep 27 2010 He's using std.stream.File, not std.stdio.File.
- Tom Kazimiers (7/14) Sep 28 2010 I'll keep that in mind and will go for a cleanup method that I have to
Hi,
a file reading class of mine can be constructed with a filename as
parameter. It instantiates a new std.stream.File (without the passed
file name and closes it when opened within the destructor. The last part
is where things are getting unclear for me. On the "file.isOpen()" call
in the destructor a segmentation fault occurs. What is the problem with
that?
Thanks in advance,
Tom
An example class to demonstrate the problem:
import std.stdio;
import std.string;
import std.stream;
class FileReader(T) {
string filename; // the name of the object file
std.stream.File file; // the object file
public:
this(string filename) {
// make an immutable copy of the filename
this.filename = filename.idup;
file = new std.stream.File();
}
// destructor
~this() {
if(file.isOpen()) // <---- crashes here
writefln("open");
}
// open file, return true if successful
bool open() {
try {
file = new std.stream.File(filename, FileMode.In);
} catch(OpenException e) {
writefln("[Error] Could not open file: " ~ filename);
return false;
}
return true;
}
}
Sep 26 2010
Tom Kazimiers <2voodoo gmx.de> wrote:Hi, a file reading class of mine can be constructed with a filename as parameter. It instantiates a new std.stream.File (without the passed file name and closes it when opened within the destructor. The last part is where things are getting unclear for me. On the "file.isOpen()" call in the destructor a segmentation fault occurs. What is the problem with that?Likely, it is this[1]: "[T]he order in which the garbage collector calls destructors for unreference objects is not specified. This means that when the garbage collector calls a destructor for an object of a class that has members that are references to garbage collected objects, those references may no longer be valid. This means that destructors cannot reference sub objects." [1]: http://digitalmars.com/d/2.0/class.html#destructors -- Simen
Sep 26 2010
Hi Simen, On 09/26/2010 04:06 PM, Simen kjaeraas wrote:Likely, it is this[1]: "[T]he order in which the garbage collector calls destructors for unreference objects is not specified. This means that when the garbage collector calls a destructor for an object of a class that has members that are references to garbage collected objects, those references may no longer be valid. This means that destructors cannot reference sub objects." [1]: http://digitalmars.com/d/2.0/class.html#destructorsthanks for your reply. I did not know that the garbage collector works that way. Is the reason for that flexibility for the GC? What if I want to handle some destruction parts to sub-objects or if I want conditions while destruction, based on sub-objects? Or maybe I should generally avoid situations like that. Do you have any suggestion how I should make sure that the file gets closed on destruction? Cheers, Tom
Sep 26 2010
Tom Kazimiers:Do you have any suggestion how I should make sure that the file gets closed on destruction?Can you use scope(exit) or the std.stdio.File? Bye, bearophile
Sep 26 2010
Hi, On 09/26/2010 07:13 PM, bearophile wrote:Tom Kazimiers:Well, I have no idea. You mentioning scope(exit) was actually the first time I heard of it. Unfortunately I have not found any resource about it. Do you have a link to point me in the right direction? If I would use std.stdio.File, what would be different? Thanks, TomDo you have any suggestion how I should make sure that the file gets closed on destruction?Can you use scope(exit) or the std.stdio.File?
Sep 26 2010
Tom Kazimiers <2voodoo gmx.de> wrote:Hi, On 09/26/2010 07:13 PM, bearophile wrote:http://digitalmars.com/d/2.0/statement.html#ScopeGuardStatement -- SimenTom Kazimiers:Well, I have no idea. You mentioning scope(exit) was actually the first time I heard of it. Unfortunately I have not found any resource about it. Do you have a link to point me in the right direction?Do you have any suggestion how I should make sure that the file gets closed on destruction?Can you use scope(exit) or the std.stdio.File?
Sep 26 2010
Tom Kazimiers <2voodoo gmx.de> Hi, On 09/26/2010 10:05 PM, Simen kjaeraas wrote:thanks, strange I did not find that page by searching. Good to know about that concept, but I guess it is not fitting as a solution here. My scope is the from creation to destrution of the class, so this will no be working. But anyway, thanks. Tomhttp://digitalmars.com/d/2.0/statement.html#ScopeGuardStatementCan you use scope(exit) or the std.stdio.File?Well, I have no idea. You mentioning scope(exit) was actually the first time I heard of it. Unfortunately I have not found any resource about it. Do you have a link to point me in the right direction?
Sep 28 2010
On Sun, 26 Sep 2010 20:55:33 +0200, Tom Kazimiers wrote:If I would use std.stdio.File, what would be different?Well, for one thing you won't have to write your code all over again when std.stream is deprecated, which will happen soon. std.stdio.File is really what you should use for file I/O in new code. That said, there's a chance it does exactly what you want. You don't have to open a file on construction, there's an open() function which opens a file and assigns it to the File handle. Nor do you have to worry about closing the file in the destructor, as it is automatically closed the moment the last reference to it goes out of scope. Here are a few examples of how to use it: File file; // File's a struct, so no need to use 'new' // Read a text file line by line file.open("foo.txt"); foreach (line; file.byLine()) writeln(line); // Read a binary file in 4MB chunks file.open("foo.dat"); foreach (ubyte[] chunk; file.byChunk(4*1024)) doStuffWith(chunk); // Read up to 100 ints from a file file.open("myInts"); auto buffer = new int[100]; auto data = file.rawRead(buffer); -Lars
Sep 27 2010
Tom Kazimiers wrote:Hi Simen, On 09/26/2010 04:06 PM, Simen kjaeraas wrote:The way I see it, there are two possible situations: 1. You really need precise control as to when the file is closed. In that case, your class contains an explicit cleanup function that you call before dropping the last reference and you can close the file at that time; 2. You only need to be sure that the file gets closed at some point but it doesn't really signify when. In that case, you let the GC collect your class and you don't close the file. Eventually the GC will collect the std.stream.File instance which will result in calling its destructor which will close the file without your needing to do anything about it. Jerome -- mailto:jeberger free.fr http://jeberger.free.fr Jabber: jeberger jabber.frLikely, it is this[1]: "[T]he order in which the garbage collector calls destructors for unreference objects is not specified. This means that when the garbage collector calls a destructor for an object of a class that has members that are references to garbage collected objects, those references may no longer be valid. This means that destructors cannot reference sub objects." [1]: http://digitalmars.com/d/2.0/class.html#destructorsthanks for your reply. I did not know that the garbage collector works that way. Is the reason for that flexibility for the GC? What if I want to handle some destruction parts to sub-objects or if I want conditions while destruction, based on sub-objects? Or maybe I should generally avoid situations like that. Do you have any suggestion how I should make sure that the file gets closed on destruction?
Sep 26 2010
Hi Jérôme, On 09/26/2010 10:59 PM, "Jérôme M. Berger" wrote:The way I see it, there are two possible situations: 1. You really need precise control as to when the file is closed. In that case, your class contains an explicit cleanup function that you call before dropping the last reference and you can close the file at that time; 2. You only need to be sure that the file gets closed at some point but it doesn't really signify when. In that case, you let the GC collect your class and you don't close the file. Eventually the GC will collect the std.stream.File instance which will result in calling its destructor which will close the file without your needing to do anything about it.That are probably the two choices I have, yes. I already have such a cleanup function and will probably go for that. Thanks, Tom
Sep 28 2010
On Sun, 26 Sep 2010 11:17:07 -0400, Tom Kazimiers <2voodoo gmx.de> wrote:Hi Simen, On 09/26/2010 04:06 PM, Simen kjaeraas wrote:Then do not use a destructor. There is no way currently for the destructor to know whether it's being called from the GC or not, so it is only safe to destroy resources *not* allocated by the GC. In fact, the only reason destructors are supported in classes is to destroy non-GC resources.Likely, it is this[1]: "[T]he order in which the garbage collector calls destructors for unreference objects is not specified. This means that when the garbage collector calls a destructor for an object of a class that has members that are references to garbage collected objects, those references may no longer be valid. This means that destructors cannot reference sub objects." [1]: http://digitalmars.com/d/2.0/class.html#destructorsthanks for your reply. I did not know that the garbage collector works that way. Is the reason for that flexibility for the GC? What if I want to handle some destruction parts to sub-objects or if I want conditions while destruction, based on sub-objects?Or maybe I should generally avoid situations like that. Do you have any suggestion how I should make sure that the file gets closed on destruction?You don't have to worry about it -- let the GC do its job. If you think about it, your class instance may have the only reference to the File object. Since your class is being destroyed by the GC, it makes sense that the File object has no references to it, so it too is being destroyed by the GC. If you want sooner destruction, you should manually close it earlier via another function call (like close() or detach()). However, I will mention something that others missed, unlike in C++, the default protection in a class is public, so your public: attribute doesn't do much, and your file member is publicly accessible. -Steve
Sep 27 2010
On 2010-09-26 10:06:33 -0400, "Simen kjaeraas" <simen.kjaras gmail.com> said:Tom Kazimiers <2voodoo gmx.de> wrote:That's it indeed, but I'll add that it's the File struct that is at fault. See this bug: <http://d.puremagic.com/issues/show_bug.cgi?id=4624> To make it short: when the File struct is located somewhere in the GC heap (like inside a class), File's destructor is buggy when a file is open. The only workaround I can think of is to call close() or detach() on the file struct before the garbage collectors kicks in (doing it in the destructor of your class is already too late, it must be done before the destructor gets called). In fact, it's generally a good idea to not wait for the GC to collect your objects before closing files, because waiting for the GC could take an indeterminate amount of time and leave files open for a long time (the GC only runs when needed). -- Michel Fortin michel.fortin michelf.com http://michelf.com/Hi, a file reading class of mine can be constructed with a filename as parameter. It instantiates a new std.stream.File (without the passed file name and closes it when opened within the destructor. The last part is where things are getting unclear for me. On the "file.isOpen()" call in the destructor a segmentation fault occurs. What is the problem with that?Likely, it is this[1]: "[T]he order in which the garbage collector calls destructors for unreference objects is not specified. This means that when the garbage collector calls a destructor for an object of a class that has members that are references to garbage collected objects, those references may no longer be valid. This means that destructors cannot reference sub objects." [1]: http://digitalmars.com/d/2.0/class.html#destructors
Sep 26 2010
On Sun, 26 Sep 2010 20:20:18 -0400, Michel Fortin <michel.fortin michelf.com> wrote:On 2010-09-26 10:06:33 -0400, "Simen kjaeraas" <simen.kjaras gmail.com> said:He's using std.stream.File, not std.stdio.File.Tom Kazimiers <2voodoo gmx.de> wrote:That's it indeed, but I'll add that it's the File struct that is at fault. See this bug: <http://d.puremagic.com/issues/show_bug.cgi?id=4624>Hi, a file reading class of mine can be constructed with a filename as parameter. It instantiates a new std.stream.File (without the passed file name and closes it when opened within the destructor. The last part is where things are getting unclear for me. On the "file.isOpen()" call in the destructor a segmentation fault occurs. What is the problem with that?Likely, it is this[1]: "[T]he order in which the garbage collector calls destructors for unreference objects is not specified. This means that when the garbage collector calls a destructor for an object of a class that has members that are references to garbage collected objects, those references may no longer be valid. This means that destructors cannot reference sub objects." [1]: http://digitalmars.com/d/2.0/class.html#destructorsIn fact, it's generally a good idea to not wait for the GC to collect your objects before closing files, because waiting for the GC could take an indeterminate amount of time and leave files open for a long time (the GC only runs when needed).Yes, this is true no matter what File construct you use. -Steve
Sep 27 2010
Hi, On 09/27/2010 02:09 PM, Steven Schveighoffer wrote:On Sun, 26 Sep 2010 20:20:18 -0400, Michel FortinI'll keep that in mind and will go for a cleanup method that I have to call explicitely. Especially files should probably only be opened if in use or if one wants to prevent others from using it. Cheers, TomIn fact, it's generally a good idea to not wait for the GC to collect your objects before closing files, because waiting for the GC could take an indeterminate amount of time and leave files open for a long time (the GC only runs when needed).Yes, this is true no matter what File construct you use.
Sep 28 2010