关于parallelStream()引发线程不安全问题

向右看齐 2023-07-17 04:55 47阅读 0赞

一、问题代码

public class ParallelStreamTest {
        public static void main(String[] args) {
            List<DataA> dataAList  =new ArrayList<>();
            List<DataB> dataBList = new ArrayList<>();
            for (int i = 0; i <5 ; i++) {
                DataA a = new DataA();
                if (i>3){
                    a.setId("111");
                }else {
                    a.setId("222");
                }
                dataAList.add(a);
            }
    
            for (int i = 0; i <100 ; i++) {
                DataB b = new DataB();
                if (i>50){
                    b.setId("111");
                }else {
                    b.setId("222");
                }
                dataBList.add(b);
            }
    
            List<DataC> dataCList = getDataC(dataAList,dataBList);
            System.out.println(dataCList.toString());
    
        }
    
        private static List<DataC> getDataC(List<DataA> dataAList, List<DataB> dataBList){
            List<DataC> dataCList = new ArrayList<>();
            dataBList.parallelStream().forEach(b->{
                DataA a =  dataAList.parallelStream().filter(aa->aa.id.equals(b.id)).findFirst().orElse(new DataA());
                DataC c = new DataC();
                c.setId(a.id);
                dataCList.add(c);
            });
            return dataCList;
    
        }
    
        static class DataA{
            private String id;
    
            public String getId() {
                return id;
            }
    
            public void setId(String id) {
                this.id = id;
            }
        }
    
        static class DataB{
            private String id;
    
            public String getId() {
                return id;
            }
    
            public void setId(String id) {
                this.id = id;
            }
        }
    
        static class DataC{
            private String id;
    
            public String getId() {
                return id;
            }
    
            public void setId(String id) {
                this.id = id;
            }
        }
    }

二、执行结果

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2h5X2NvbWluZw_size_16_color_FFFFFF_t_70][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2h5X2NvbWluZw_size_16_color_FFFFFF_t_70 1][]

每次执行结果不统一

三、解决办法

private static List<DataC> getDataC(List<DataA> dataAList, List<DataB> dataBList){
            List<DataC> dataCList = new ArrayList<>();
            dataBList.forEach(b->{
                DataA a =  dataAList.stream().filter(aa->aa.id.equals(b.id)).findFirst().orElse(new DataA());
                DataC c = new DataC();
                c.setId(a.id);
                dataCList.add(c);
            });
            return dataCList;
    
        }

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2h5X2NvbWluZw_size_16_color_FFFFFF_t_70 2][]

去掉parallelStream()每次执行结果一致

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2h5X2NvbWluZw_size_16_color_FFFFFF_t_70]: /images/20230528/644165b61cc8496abcc3b328b7db208f.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2h5X2NvbWluZw_size_16_color_FFFFFF_t_70 1]: /images/20230528/3b94f90fe3bb4f44a3005b446ac9b0dd.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2h5X2NvbWluZw_size_16_color_FFFFFF_t_70 2]: /images/20230528/39548647871d407495d37e4322ff5f4a.png