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golang将指针传给cgo后还能被回收吗？

article 2024/10/28 7:03:22

问题：

如果把golang分配的变量，其指针通过cgo传给c，并被c存储，那这个变量还能被gc回收吗？

实验代码：

test_memory_leak.go

package main

/*
#include <stdlib.h>
#include <string.h>
#include <stdio.h>

char* cMalloc() {
	char *mem = (char*)malloc(1024 * 1024 * 16);
	return mem;
}

void cMemset(char* mem) {
	memset(mem, '-', 1024 * 1024 * 16);
}

int arrLen = 1000;
int arrIndex;
char* globalMemAddr[1000];

void printAddr(char* mem) {
	if (arrIndex+1 >= arrLen) {
		arrIndex = 0;
	} else {
		arrIndex++;
	}
	globalMemAddr[arrIndex] = mem;
	printf("index: %d, addr: %p\n", arrIndex, globalMemAddr[arrIndex]);
}
*/
import "C"
import (
	"fmt"
	"net/http"
	_ "net/http/pprof"
	"os"
	"sync"
	"time"
	"unsafe"
)

var size int = 1024 * 1024 * 16

func main() {
	go func() {
		_ = http.ListenAndServe("0.0.0.0:9091", nil)
	}()
	if len(os.Args) > 1 && os.Args[1] == "1" {
		var wg sync.WaitGroup
		for {
			wg.Add(1)
			go doCMalloc(&wg)
			wg.Wait()
			time.Sleep(500 * time.Millisecond)
		}
	} else {
		var wg sync.WaitGroup
		for {
			wg.Add(1)
			go doGoMalloc(&wg)
			wg.Wait()
			time.Sleep(500 * time.Millisecond)
		}
	}
}

// 无泄漏
func doCMalloc(wg *sync.WaitGroup) {
	defer wg.Done()
	cptr := C.cMalloc()
	C.cMemset(cptr)
	C.printAddr(cptr)
	bs := C.GoBytes(unsafe.Pointer(cptr), C.int(size))
	fmt.Printf("1: %s .. %s\n", string(bs[0:8]), string(bs[size-8:size]))
	C.free(unsafe.Pointer(cptr))
}

// 无泄漏
func doGoMalloc(wg *sync.WaitGroup) {
	defer wg.Done()
	bs := make([]byte, size, size)
	cptr := (*C.char)(unsafe.Pointer(&bs[0]))
	C.cMemset(cptr)
	C.printAddr(cptr)
	fmt.Printf("2: %s .. %s\n", string(bs[0:8]), string(bs[size-8:size]))
}