Hi Ian,
syslogparser.go
=============
func (obj SyslogParser) LoadPatternDB(opts Syslog, workerId int) {
patterndbpath := C.CString(opts.Patterndb) . <<<<<<<<<<<<<<< . STEP 1
defer C.free(unsafe.Pointer(patterndbpath)) . <<<<<<<<<<<<<<<< STEP 2
InitStruct := (*C.Accumulatedparams)(C.calloc(1,
C.sizeof_struct_Accumulatedparams))
InitStruct.callback = (C.key_value_cb)(C.callback)
InitStruct.data = C.int(workerId)
C.load_pattern_db(patterndbpath,
(*C.Accumulatedparams)(unsafe.Pointer(InitStruct)), C.int(workerId))
}
Since I am running this program in multiple go routines, when we do above
STEP 1 :
1)Will the C memory allocate different addresses for 'patterndbpath' in
both the routines ...Am I right ?
2)You said 'It may be calling free twice on the same pointer', but I am
assigning a different pointer in STEP 1 everytime for each routine...Am I
right ?
3)Is it possible that one Go routine has already freed up the address that
the other Go routine is trying to free and that is causing this 'fatal
error: bin/main': double free or corruption (fasttop)'
Is this because of the race condition between two routines that this error
is seen ?
4)If you show us a small, complete, self-contained example, that does not
call any other code, then we may be able to see the problem.
>> As you have mentioned problem is happening when we call 'C.free'.Do you
mean by not calling internal syslog-ng methods and just calling a normal C
program with multiple go routines ?
Please correct me here if I am wrong
Thanks,
Nitish
On Fri, Jul 12, 2019 at 11:00 AM Ian Lance Taylor <i...@golang.org> wrote:
> On Thu, Jul 11, 2019 at 8:45 PM Nitish Saboo <nitish.sabo...@gmail.com>
> wrote:
> >
> > I have the following function 'LoadPatternDB' where I am allocating
> memory for a C struct.My C struct contains the callback function.
> > I have the function 'LoadPatternDB' that is running in multiple go
> routines.I have written a C wrapper that internally uses syslog-ng methods.
> > While running the method 'LoadPatternDB' in syslogparser.go with
> multiple go routines, I get the following error.
> >
> > *** Error in `fatal error: bin/main': double free or corruption
> (fasttop)unexpected signal during runtime execution: 0x00007fd2b8588060 ***
> >
> > My queries are:
> >
> > 1)When do we get this error ?
>
> That error is from the C memory allocator. It does not come from Go.
> It means that you called a C function such as malloc, calloc, or free,
> and the call detected memory corruption. It may be calling free twice
> on the same pointer, or it may be using a dangling pointer, or it may
> be some other memory corruption. We don't know.
>
> > 2)Is it because of not deallocating the struct memory, I am getting this
> error ?But at the same time I am allocating separate memories for each of
> the go routines.
>
> No.
>
> > 3)Is it because of the memory crunch on the system that can lead to this
> error ?
>
> Unlikely. It is conceivable that malloc or calloc is returning NULL,
> and you are not checking for NULL, and that is leading to memory
> corruption. But that is unlikely to happen, and it is unlikely to
> cause this kind of error.
>
> > 4)The issues is seen with only multiple go routines.Single iteration of
> the code is working fine.
>
> That sounds like a good place to start looking.
>
> > 5)Can I not call Go code and C code using multiple threads ?
>
> You can call C code from multiple goroutines, but of course the C code
> has to be prepared to handle it. It's no different from a C program
> that calls the C function from multiple threads.
>
> If you show us a small, complete, self-contained example, that does
> not call any other code, then we may be able to see the problem.
>
> Ian
>
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