input: Implement second callback to deallocate heap memory that is

allocated by C style (C.calloc)

Signed-off-by: Hiroshi Hatake <hatake@calyptia.com>

Author: cosmo0920

examples/in_gdummy/README.md

@@ -7,12 +7,13 @@ specified instance configuration to the input callback.
 
 Every output plugin go through four callbacks associated to different phases:
 
-| Plugin Phase        | Callback                   |
-|---------------------|----------------------------|
-| Registration        | FLBPluginRegister()        |
-| Initialization      | FLBPluginInit()            |
-| Input Callback      | FLBPluginInputCallback()   |
-| Exit                | FLBPluginExit()            |
+| Plugin Phase           | Callback                        |
+|------------------------|---------------------------------|
+| Registration           | FLBPluginRegister()             |
+| Initialization         | FLBPluginInit()                 |
+| Input Callback         | FLBPluginInputCallback()        |
+| Input Cleanup Callback | FLBPluginInputCleanupCallback() |
+| Exit                   | FLBPluginExit()                 |
 
 ## Plugin Registration
 
@@ -58,10 +59,6 @@ func alloc(size int) unsafe.Pointer {
 func makeSlice(p unsafe.Pointer, n int) *Slice {
 	data := &c_slice_t{p, n}
 
-	runtime.SetFinalizer(data, func(data *c_slice_t){
-		C.free(data.p)
-	})
-
 	s := &Slice{data: data}
 	h := (*reflect.SliceHeader)(unsafe.Pointer(&s.Data))
 	h.Data = uintptr(p)
@@ -93,6 +90,29 @@ func FLBPluginInputCallback(data **C.void, size *C.size_t) int {
 }
 ```
 
+### Input Cleanup Callback
+
+For cleaning up to be allocated resources, this callback will be triggered after _Input Callback_.
+
+This callback is mainly used for deallocating heap memories which are allocated by `C.malloc` or `C.calloc`.
+
+```go
+import "sync"
+
+var barrior sync.Mutex
+
+//export FLBPluginInputCleanupCallback
+func FLBPluginInputCleanupCallback(data unsafe.Pointer) int {
+	barrior.Lock() // Guarding for deallocating region is needed for safety.
+	C.free(unsafe.Pointer(data))
+	barrior.Unlock()
+
+	return input.FLB_OK
+}
+```
+
+#### Returning Status Values
+
 > for more details about how to process the sending msgpack data into Fluent Bit core, please refer to the [in_gdummy.go](in_gdummy.go) file.
 
 When done, there are three returning values available:
@@ -103,6 +123,7 @@ When done, there are three returning values available:
 | FLB\_ERROR    | An internal error have ocurred, the plugin will not handle the set of records/data again. |
 | FLB\_RETRY    | A recoverable error have ocurred, the engine can try to flush the records/data later.|
 
+
 ## Plugin Exit
 
 When Fluent Bit will stop using the instance of the plugin, it will trigger the exit callback. e.g:

examples/in_gdummy/in_gdummy.go

@@ -8,7 +8,7 @@ import (
 	"fmt"
 	"time"
 	"reflect"
-	"runtime"
+	"sync"
 	"unsafe"
 
 	"github.com/fluent/fluent-bit-go/input"
@@ -24,6 +24,8 @@ type c_slice_t struct {
 	n int
 }
 
+var barrior sync.Mutex
+
 //export FLBPluginRegister
 func FLBPluginRegister(def unsafe.Pointer) int {
 	return input.FLBPluginRegister(def, "gdummy", "dummy GO!")
@@ -44,11 +46,7 @@ func alloc(size int) unsafe.Pointer {
 }
 
 func makeSlice(p unsafe.Pointer, n int) *Slice {
-	data := &c_slice_t{p, n}
-
-	runtime.SetFinalizer(data, func(data *c_slice_t){
-		C.free(data.p)
-	})
+	data := &c_slice_t{p: p, n: n}
 
 	s := &Slice{data: data}
 	h := (*reflect.SliceHeader)(unsafe.Pointer(&s.Data))
@@ -86,6 +84,15 @@ func FLBPluginInputCallback(data *unsafe.Pointer, size *C.size_t) int {
 	return input.FLB_OK
 }
 
+//export FLBPluginInputCleanupCallback
+func FLBPluginInputCleanupCallback(data unsafe.Pointer) int {
+	barrior.Lock()
+	C.free(unsafe.Pointer(data))
+	barrior.Unlock()
+
+	return input.FLB_OK
+}
+
 //export FLBPluginExit
 func FLBPluginExit() int {
 	return input.FLB_OK