BinaryOracle commented 12 months ago

问题描述

项目路径下提供了一个测试用例文件: sys_exec_test.go , 其中提供了一个测试函数TestReadv，用于测试Readv系统调用：

func TestReadv(t *testing.T) {
    // 1. 向fd中写入数据
    r, w := GetSysFdPairs()
    vs := [][]byte{
        []byte("first line"),  // len=10
        []byte("second line"), // len=11
        []byte("third line"),  // len=10
    }
    w1, _ := syscall.Write(w, vs[0])
    w2, _ := syscall.Write(w, vs[1])
    w3, _ := syscall.Write(w, vs[2])
    Equal(t, w1+w2+w3, 31)

    // 2. 准备bs和ivs缓冲区
    var barrier = barrier{}
    barrier.bs = [][]byte{
        make([]byte, 0),
        make([]byte, 10),
        make([]byte, 11),
        make([]byte, 10),
    }
    barrier.ivs = make([]syscall.Iovec, len(barrier.bs))
    // 3. 调用readv系统调用,读取数据到ivs , ivs缓冲区指针指向了bs
    rn, err := readv(r, barrier.bs, barrier.ivs)
    MustNil(t, err)
    Equal(t, rn, 31)
    // 4. 打印bs缓冲区中的数据
    for i, v := range barrier.bs {
        t.Logf("READ [%d] %s", i, v)
    }
}

在没有修改前，readv的源码如下:

// readv wraps the readv system call.
// return 0, nil means EOF.
func readv(fd int, bs [][]byte, ivs []syscall.Iovec) (n int, err error) {
        // 依次为每个ivs[i].base 与 bs[i] 建立映射关系
    iovLen := iovecs(bs, ivs)
    if iovLen == 0 {
        return 0, nil
    }
    // syscall
    r, _, e := syscall.RawSyscall(syscall.SYS_READV, uintptr(fd), uintptr(unsafe.Pointer(&ivs[0])), uintptr(iovLen))
        // 此处会清空bs和ivs缓冲区
    resetIovecs(bs, ivs[:iovLen])
    if e != 0 {
        return int(r), syscall.Errno(e)
    }
    return int(r), nil
}

最终输出的结果为 , 缓冲区中的数据为空，都被清空了，不符合预期:

=== RUN   TestReadv
    sys_exec_test.go:120: READ [0] 
    sys_exec_test.go:120: READ [1] 
    sys_exec_test.go:120: READ [2] 
    sys_exec_test.go:120: READ [3] 
--- PASS: TestReadv (0.00s)
PASS

解决办法

将readv中清空缓冲区的方法调用移除:

// readv wraps the readv system call.
// return 0, nil means EOF.
func readv(fd int, bs [][]byte, ivs []syscall.Iovec) (n int, err error) {
    iovLen := iovecs(bs, ivs)
    if iovLen == 0 {
        return 0, nil
    }
    // syscall
    r, _, e := syscall.RawSyscall(syscall.SYS_READV, uintptr(fd), uintptr(unsafe.Pointer(&ivs[0])), uintptr(iovLen))
    if e != 0 {
        return int(r), syscall.Errno(e)
    }
    return int(r), nil
}

再次运行测试用例，输出如下:

=== RUN   TestReadv
    sys_exec_test.go:124: READ [0] 
    sys_exec_test.go:124: READ [1] first line
    sys_exec_test.go:124: READ [2] second line
    sys_exec_test.go:124: READ [3] third line
--- PASS: TestReadv (0.00s)
PASS

CLAassistant commented 12 months ago

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joway commented 12 months ago

@BinaryOracle 这个其实是这段测试有点问题。原本的代码没问题。之所以要reset，是因为 barrier 不能持有原始 []byte 的引用，否则这段 []byte 永远不能被 GC

BinaryOracle commented 12 months ago

@BinaryOracle 这个其实是这段测试有点问题。原本的代码没问题。之所以要reset，是因为 barrier 不能持有原始 []byte 的引用，否则这段 []byte 永远不能被 GC

我改了一下pr，把TestReadv测试函数修正了一下:

func TestReadv(t *testing.T) {
    r, w := GetSysFdPairs()
    vs := [][]byte{
        []byte("first line"),  // len=10
        []byte("second line"), // len=11
        []byte("third line"),  // len=10
    }
    w1, _ := syscall.Write(w, vs[0])
    w2, _ := syscall.Write(w, vs[1])
    w3, _ := syscall.Write(w, vs[2])
    Equal(t, w1+w2+w3, 31)

    var barrier = barrier{
        bs: make([][]byte, 4),
    }
    res := [][]byte{
        make([]byte, 0),
        make([]byte, 10),
        make([]byte, 11),
        make([]byte, 10),
    }
    for i := range res {
        barrier.bs[i] = res[i]
    }
    barrier.ivs = make([]syscall.Iovec, len(barrier.bs))
    rn, err := readv(r, barrier.bs, barrier.ivs)
    MustNil(t, err)
    Equal(t, rn, 31)
    for i, v := range res {
        t.Logf("READ [%d] %s", i, v)
    }
}

joway commented 12 months ago

@BinaryOracle Hi，能再辛苦你能签署下这个吗？