广州网站设计素材,手机商城网站模板,电子商务营销,桂林市中考信息网官网问题描述#xff1a;
在go程序中#xff0c;通过执行一个命令启动一个子命令#xff0c;并通过pipe读取子程序的标准输入和输出#xff0c;通过scanner默认按行读取#xff0c;此时如果子程序输出时没有携带’\n’#xff0c;scanner就不会打印输出#xff0c;而是会累…问题描述
在go程序中通过执行一个命令启动一个子命令并通过pipe读取子程序的标准输入和输出通过scanner默认按行读取此时如果子程序输出时没有携带’\n’scanner就不会打印输出而是会累积到缓存buf上限最终被丢弃直到遇到一个\n然后输出所有的内容默认buf缓存上限时65536如果日志打印处还有限制如glog就限制最大的打印字节数为4096那么就会导致日志再次丢失。
解决方法
不适用scanner去按行读取直接读取管道的内容然后设置上限超过时或者遇到’\n’时打印
测试代码
子程序
#include stdio.h
#include unistd.hint main() {
int count 0;while (1) {fprintf(stderr, %d, count);count (count 1) % 10;usleep(500); // Sleep for 500,000 microseconds (0.5 seconds)
}return 0;
}主程序
package mainimport (bufiofmtos/execstringslog
)func main() {cmd : exec.Command(./test)stdout, err : cmd.StdoutPipe()if err ! nil {fmt.Println(Error creating StdoutPipe:, err)return}cmd.Stderr cmd.Stdouterr cmd.Start()if err ! nil {fmt.Println(Error starting command:, err)return}scanner : bufio.NewScanner(stdout)// scanner.Split(bufio.ScanBytes)// buf : // for scanner.Scan() {// buf scanner.Text()// if strings.Contains(buf, \n) || len(buf) 256 {// log.Printf(%s, buf)// buf // }// }for scanner.Scan() {log.Printf(%s, scanner.Text())}if err : scanner.Err(); err ! nil {fmt.Println(Error reading standard output:, err)}err cmd.Wait()if err ! nil {fmt.Println(Error waiting for command to finish:, err)}
}
修改程序
package mainimport (bufiofmtiologos/exec
)func getReaderSize(rd io.Reader) {b, ok : rd.(*bufio.Reader)if ok {log.Printf(rd size: %d, b.Size())} else {log.Printf(rd is not bufio.Reader)}
}func main() {// Command to executecmd : exec.Command(./test)// Create a pipe to capture the standard output of the commandstdout, err : cmd.StdoutPipe()if err ! nil {fmt.Println(Error creating StdoutPipe:, err)return}cmd.Stderr cmd.Stdout// Start the commanderr cmd.Start()if err ! nil {fmt.Println(Error starting command:, err)return} Create a scanner to read the commands standard output//scanner : bufio.NewScanner(stdout)//scanner.Split(bufio.ScanBytes)// Read and print each line from the output//buf : make([]byte, 256)//bufLen : 0//for scanner.Scan() {// buf[bufLen] scanner.Bytes()[0]// // buf append(buf, scanner.Bytes()...)// bufLen 1// if buf[bufLen-1] \n || bufLen 256 {// log.Printf(%s, string(buf[:bufLen]))// bufLen 0// }//}// Check for errors in scanning//if err : scanner.Err(); err ! nil {// fmt.Println(Error reading standard output:, err)//}// Create a buffered reader to read from the commands stdoutreader : bufio.NewReaderSize(stdout, 256)getReaderSize(stdout)log.Printf(reader size: %d, reader.Size()) Buffer to store incomplete lines//var incompleteLine []byte// Buffer to read chunks of bytes//chunk : make([]byte, 256)////for {// // Read a chunk of bytes// n, err : reader.Read(chunk)// if err ! nil {// break // Break the loop when an error occurs (e.g., when the command finishes)// }//// // Process each byte in the chunk// for i : 0; i n; i {// b : chunk[i]//// // Check for newline or length exceeding 256// if b \n || len(incompleteLine) 256 {// // Print the line// log.Printf(%s, incompleteLine)//// // Reset the incomplete line buffer// incompleteLine nil// } else {// // Add the byte to the incomplete line buffer// incompleteLine append(incompleteLine, b)// }// }//}for {s, err : reader.ReadSlice(\n)if err ! nil err ! bufio.ErrBufferFull {if len(s) 0 {log.Printf(reader err but exist data, reader size: %d, read string size: %d, string: %s, reader.Size(), len(s), string(s))}fmt.Println(Error reader ReadString:, err)break // Break the loop when an error occurs (e.g., when the command finishes)}log.Printf(reader size: %d, read string size: %d, string: %s, reader.Size(), len(s), string(s))}// Wait for the command to finisherr cmd.Wait()if err ! nil {fmt.Println(Error waiting for command to finish:, err)}
}
benchmark test:
package mainimport (strconvstringstesting
)func stringTest1() string {var buf stringfor i : 0; i 256; i {buf strconv.Itoa(i)}return buf
}func stringTest2() string {var buf strings.Builderfor i : 0; i 256; i {buf.Write([]byte(strconv.Itoa(i)))}return buf.String()
}func stringTest3() string {var buf make([]byte, 0)for i : 0; i 256; i {buf append(buf, []byte(strconv.Itoa(i))...)}return string(buf)
}func stringTest4() string {var buf make([]byte, 256)for i : 0; i 256; i {buf[i] 1}return string(buf)
}func BenchmarkStringTest1(b *testing.B) {for i : 0; i b.N; i {stringTest1()}
}
func BenchmarkStringTest2(b *testing.B) {for i : 0; i b.N; i {stringTest2()}
}
func BenchmarkStringTest3(b *testing.B) {for i : 0; i b.N; i {stringTest3()}
}
func BenchmarkStringTest4(b *testing.B) {for i : 0; i b.N; i {stringTest4()}
}benchmark test cmd:
go test -bench . -benchmem
go test -benchfunction
