This is the code snippet I was talking about:
store := make([]*C.struct_Accumulatedparams, 2)
func (obj Syslogparser) LoadPatternDB(opts Syslog) {
>
> patterndb_path := C.CString(opts.patterndb)
> store[0] = (*C.Accumulatedparams)(C.calloc(1,
C.sizeof_struct_Accumulatedparams))
> store[0].callback = (C.key_value_cb)(C.callOnMeGo_cgo)
> store[0].data = C.int(1)
> C.load_pattern_db(patterndb_path,
(*C.Accumulatedparams)(unsafe.Pointer(store[0])))
> }
On Fri, 12 Jul 2019, 00:22 Nitish Saboo, <nitish.sabo...@gmail.com> wrote:
> Hi Ian,
>
> Can you please guide me with the correct way to store the address of a C
> struct in a Go array so that I can use it later for deallocating the memory?
>
> Thanks,
> Nitish
>
> On Fri, 12 Jul 2019, 00:04 Ian Lance Taylor, <i...@golang.org> wrote:
>
>> On Thu, Jul 11, 2019 at 10:58 AM Nitish Saboo <nitish.sabo...@gmail.com>
>> wrote:
>> >
>> > pattern_db_set_emit_func(patterndb[workerId],
>> pdbtool_pdb_emit_accumulate, cb);
>> > suggests that cb is being saved away for future use.
>> >
>> > >>>>yes cb is being saved away and is being used for future use for
>> callbacks to Go code.
>>
>> Then clearly the Go code must not immediately free the C memory. That
>> is no different from how C code would work.
>>
>>
>> > syslog-node.h
>> > ============
>> >
>> > #ifndef TEST_H_INCLUDED
>> > #define TEST_H_INCLUDED
>> >
>> > #include <stdlib.h>
>> > typedef void (*key_value_cb)(const char* key, const char* value,
>> size_t value_len, int data);
>> > typedef struct Accumulatedparams{
>> > key_value_cb callback;
>> > int data;
>> > }Accumulatedparams;
>> > int initialize_engine(const char* filename, const char* module_path);
>> > int reload_pattern_db(const char* filename, Accumulatedparams *cb, int
>> workerId);
>> > int load_pattern_db(const char* filename, Accumulatedparams *cb, int
>> workerId);
>> >
>> > >>>>>If I declare the array in the following manner:
>> >
>> > result := make([]*C.struct_Accumulatedparams)
>> > store[0] = (*C.Accumulatedparams)(C.calloc(1,
>> C.sizeof_struct_Accumulatedparams))
>> >
>> > Here also the code gets compiled successfully, just that the GoLand IDE
>> shows store[0].callback and store[0].data in red color saying Unresolved
>> reference 'callback' and Unresolved reference 'data' respectively.Not sure
>> how the code compiles if the IDE shows it in red color. Binary(./main)
>> works fine
>>
>> I don't know what the GoLand IDE does. I don't see any
>> store[0].callback or store[0].data in that code snippet.
>>
>>
>> > Though this works,
>> >
>> > store[0] = (*C.Accumulatedparams)(C.calloc(1,
>> C.sizeof_struct_Accumulatedparams))
>> > InitStruct := store[0]
>> > InitStruct.callback = (C.key_value_cb)(C.callOnMeGo_cgo)
>> > InitStruct.data = C.int(1)
>> >
>> > Here the code compiles successfully and there is no complain from
>> GoLand IDE as well.Binary (./main) too works fine
>> >
>> > So what i thought to do :
>> >
>> > type Store struct{
>> > result []*C.struct_Accumulatedparams
>> > data []C.int
>> > callback []C.key_value_cb
>> > }
>> >
>> > var store = Store{result: make([]*C.struct_Accumulatedparams, 2), data:
>> make([]C.int ,2), callback:make([]C.key_value_cb, 2)}
>> >
>> > func (obj Syslogparser) LoadPatternDB(opts Syslog) {
>> >
>> > patterndb_path := C.CString(opts.patterndb)
>> > store.result[0] = (*C.Accumulatedparams)(C.calloc(1,
>> C.sizeof_struct_Accumulatedparams)) <<<<<<
>> > store.callback[0] = (C.key_value_cb)(C.callOnMeGo_cgo) <<<<<
>> > store.data[0] = C.int(1)
>> > C.load_pattern_db(patterndb_path,
>> (*C.Accumulatedparams)(unsafe.Pointer(store.result[0])))
>> > }
>> >
>> > Here the code gets compiled successfully. But I am getting the
>> following error when I run the binary './main'
>> >
>> > 1In reload PatternDb:
>> > PatternDb :/home/nsaboo/Documents/goworkspace/src/poc/reload.xml
>> > ModulePath :usr/local/lib/syslog-ng
>> > fatal error: unexpected signal during runtime execution
>> > [signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x0]
>> >
>> > runtime stack:
>> > runtime.throw(0x4fa203, 0x2a)
>> > /usr/local/go/src/runtime/panic.go:617 +0x72
>> > runtime.sigpanic()
>> > /usr/local/go/src/runtime/signal_unix.go:374 +0x4a9
>> >
>> > goroutine 1 [syscall]:
>> > runtime.cgocall(0x4b8fb0, 0xc000042cc8, 0x4d9280)
>> > /usr/local/go/src/runtime/cgocall.go:128 +0x5b fp=0xc000042c98
>> sp=0xc000042c60 pc=0x404f6b
>> > main._Cfunc_execute_percustomer_db(0x7fb0fb5a5fa0, 0x1d5,
>> 0x7fb0fb8259b0, 0x8)
>> > _cgo_gotypes.go:121 +0x45 fp=0xc000042cc8 sp=0xc000042c98 pc=0x4b5ca5
>> > main.Syslogparser.ParseMessagePerCustomer(0xc0000a2000, 0x36, 0x4f6b0c,
>> 0x18, 0x4f3fc4, 0x8, 0xc0000d0000, 0x1d5)
>> > /home/nsaboo/Documents/goworkspace/src/poc/main.go:132 +0x109
>> fp=0xc000042d38 sp=0xc000042cc8 pc=0x4b6f09
>> > main.perCustomerParsing(...)
>> > /home/nsaboo/Documents/goworkspace/src/poc/main.go:249
>> > main.main()
>> > /home/nsaboo/Documents/goworkspace/src/poc/main.go:232 +0x6e1
>> fp=0xc000042f98 sp=0xc000042d38 pc=0x4b78e1
>> > runtime.main()
>> > /usr/local/go/src/runtime/proc.go:200 +0x20c fp=0xc000042fe0
>> sp=0xc000042f98 pc=0x42cd9c
>> > runtime.goexit()
>> > /usr/local/go/src/runtime/asm_amd64.s:1337 +0x1 fp=0xc000042fe8
>> sp=0xc000042fe0 pc=0x4548c1
>> > }
>> >
>> >
>> > Where am i going wrong here ?
>>
>> Somewhere your C code is getting a NULL pointer dereference.
>>
>> I don't see much in these questions that seems specific to Go.
>>
>> Ian
>>
>
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