digitalmars.D - Need some help with this...
- Bane <branimir.milosavljevic gmail.com> Oct 28 2009
- Jason House <jason.james.house gmail.com> Oct 28 2009
- grauzone <none example.net> Oct 28 2009
- Bane <branimir.milosavljevic gmail.com> Oct 28 2009
Following code will freeze app on std.gc.fullCollect(), when sqlite3_close() in
destructor is called. If destructor is called manualy, everything goes ok.
Is it a bug, and if is, with what? It behaves same on winxp64 and centos5.2
using dmd 1.30 and sqlite 3.6.5 or 3.6.19 statically import lib. Libraries are
tested so I do not suspect problem lies in them (they are compiled with dmc/gcc
using full threading support).
Is this some problem with GC or, more likely, my knowledge? I would appreciate
some clarification, this thing took me a lot of hours to track.
Thanks,
Bane
==========================================
import std.stdio;
import std.gc;
import std.string;
import std.thread;
pragma(lib, "sqlite3.lib");
const int SQLITE_OK = 0; // Successful result.
struct sqlite3 {}
extern(C) int sqlite3_open (char* filename, sqlite3** database);
extern(C) int sqlite3_close(sqlite3* database);
class SQLite {
sqlite3* h;
this(){
assert(sqlite3_open(toStringz(":memory:"), &h) == SQLITE_OK);
}
~this(){
writefln("~this start"); // to help debug
assert(sqlite3_close(h) == SQLITE_OK);
writefln("~this stop"); // to help debug
}
}
class T : Thread {
int run(){
SQLite s = new SQLite;
// if next line is uncommented then app wont freeze
// delete s;
return 0;
}
}
void main(){
while(true){
T t = new T;
t.start;
writefln(Thread.nthreads);
if(Thread.nthreads > 10)
fullCollect; // this will freeze app
}
}
Oct 28 2009
Jason House <jason.james.house gmail.com> Object destructors can be tricky in a GC'd language. It looks like you're accessing a deallocated pointer in your destructor. Order of collection/destruction is not guaranteed. Bane Wrote:Following code will freeze app on std.gc.fullCollect(), when sqlite3_close() in destructor is called. If destructor is called manualy, everything goes ok. Is it a bug, and if is, with what? It behaves same on winxp64 and centos5.2 using dmd 1.30 and sqlite 3.6.5 or 3.6.19 statically import lib. Libraries are tested so I do not suspect problem lies in them (they are compiled with dmc/gcc using full threading support). Is this some problem with GC or, more likely, my knowledge? I would appreciate some clarification, this thing took me a lot of hours to track. Thanks, Bane ========================================== import std.stdio; import std.gc; import std.string; import std.thread; pragma(lib, "sqlite3.lib"); const int SQLITE_OK = 0; // Successful result. struct sqlite3 {} extern(C) int sqlite3_open (char* filename, sqlite3** database); extern(C) int sqlite3_close(sqlite3* database); class SQLite { sqlite3* h; this(){ assert(sqlite3_open(toStringz(":memory:"), &h) == SQLITE_OK); } ~this(){ writefln("~this start"); // to help debug assert(sqlite3_close(h) == SQLITE_OK); writefln("~this stop"); // to help debug } } class T : Thread { int run(){ SQLite s = new SQLite; // if next line is uncommented then app wont freeze // delete s; return 0; } } void main(){ while(true){ T t = new T; t.start; writefln(Thread.nthreads); if(Thread.nthreads > 10) fullCollect; // this will freeze app } }
Oct 28 2009
Bane wrote:Following code will freeze app on std.gc.fullCollect(), when sqlite3_close() in destructor is called. If destructor is called manualy, everything goes ok. Is it a bug, and if is, with what? It behaves same on winxp64 and centos5.2 using dmd 1.30 and sqlite 3.6.5 or 3.6.19 statically import lib. Libraries are tested so I do not suspect problem lies in them (they are compiled with dmc/gcc using full threading support).
It's not your fault, it's a well known bug. The following is what happens: - in thread 1, a C function (e.g. malloc()) enters an internal lock - while thread 1 holds the lock, thread 2 triggers a D garbage collection cycle - thread 2 pauses all threads forcibly, including thread 1 - thread 2 collects some objects and calls finalizers on it - your finalizer calls a C function, which tries to enter the same lock that is held by thread 1 - but thread 1 has been paused - the GC won't resume the other threads until your function returns, and you have a deadlock As a solution, switch to D2 or Tango. These resume all suspended threads before running the finalizers.
Oct 28 2009
grauzone Wrote:Bane wrote:Following code will freeze app on std.gc.fullCollect(), when sqlite3_close() in destructor is called. If destructor is called manualy, everything goes ok. Is it a bug, and if is, with what? It behaves same on winxp64 and centos5.2 using dmd 1.30 and sqlite 3.6.5 or 3.6.19 statically import lib. Libraries are tested so I do not suspect problem lies in them (they are compiled with dmc/gcc using full threading support).
It's not your fault, it's a well known bug. The following is what happens: - in thread 1, a C function (e.g. malloc()) enters an internal lock - while thread 1 holds the lock, thread 2 triggers a D garbage collection cycle - thread 2 pauses all threads forcibly, including thread 1 - thread 2 collects some objects and calls finalizers on it - your finalizer calls a C function, which tries to enter the same lock that is held by thread 1 - but thread 1 has been paused - the GC won't resume the other threads until your function returns, and you have a deadlock As a solution, switch to D2 or Tango. These resume all suspended threads before running the finalizers.
Thank you, grauzone. That clears it. Switching to D2 or Tango is a bit overkill as existing codebase is big and fairly tested (not including this issue :). I assume this happens pretty rarely, because I haven't noticed this bug so far. Manual delete seems to be workaround, so it is not a critical issue. Thanks again :) Love D.
Oct 28 2009