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https://issues.apache.org/jira/browse/ZOOKEEPER-591?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12841941#action_12841941
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Mahadev konar commented on ZOOKEEPER-591:
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ben, did you get a chance to take a look at it ?

> The C Client cannot exit properly in some situation
> ---------------------------------------------------
>
>                 Key: ZOOKEEPER-591
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-591
>             Project: Zookeeper
>          Issue Type: Bug
>          Components: c client
>    Affects Versions: 3.2.1
>         Environment: Linux db-passport-test05.vm 2.6.9_5-4-0-5 #1 SMP Tue Apr 
> 14 15:56:24 CST 2009 x86_64 x86_64 x86_64 GNU/Linux 
>            Reporter: Qian Ye
>            Assignee: Benjamin Reed
>            Priority: Critical
>             Fix For: 3.3.0
>
>
> The following code produce a situation, where the C Client can not exit 
> properly,
> #include "include/zookeeper.h"
> void default_zoo_watcher(zhandle_t *zzh, int type, int state, const char 
> *path, void* context){
>     int zrc = 0;
>     struct String_vector str_vec = {0, NULL};
>     printf("in the default_zoo_watcher\n");
>     zrc = zoo_wget_children(zzh, "/mytest", default_zoo_watcher, NULL, 
> &str_vec);
>     printf("zoo_wget_children, error: %d\n", zrc);
>     return;
> }
> int main()
> {
>     int zrc = 0;
>     int buff_len = 10; 
>     char buff[10] = "hello";
>     char path[512];
>     struct Stat stat;
>     struct String_vector str_vec = {0, NULL};
>     zhandle_t *zh = zookeeper_init("10.81.20.62:2181", NULL, 30000, 0, 0, 0); 
>     zrc = zoo_create(zh, "/mytest", buff, 10, &ZOO_OPEN_ACL_UNSAFE, 0, path, 
> 512);
>     printf("zoo_create, error: %d\n", zrc);
>     zrc = zoo_wget_children(zh, "/mytest", default_zoo_watcher, NULL, 
> &str_vec);
>     printf("zoo_wget_children, error: %d\n", zrc);
>     zrc = zoo_create(zh, "/mytest/test1", buff, 10, &ZOO_OPEN_ACL_UNSAFE, 0, 
> path, 512);
>     printf("zoo_create, error: %d\n", zrc);
>     zrc = zoo_wget_children(zh, "/mytest", default_zoo_watcher, NULL, 
> &str_vec);
>     printf("zoo_wget_children, error: %d\n", zrc);
>     zrc = zoo_delete(zh, "/mytest/test1", -1);
>     printf("zoo_delete, error: %d\n", zrc);
>     zookeeper_close(zh);
>     return 0;
> }
> running this code can cause the program hang at zookeeper_close(zh);(line 
> 38). using gdb to attach the process, I found that the main thread is waiting 
> for do_completion thread to finish,
> (gdb) bt
> #0  0x000000302b806ffb in pthread_join () from /lib64/tls/libpthread.so.0
> #1  0x000000000040de3b in adaptor_finish (zh=0x515b60) at src/mt_adaptor.c:219
> #2  0x00000000004060ba in zookeeper_close (zh=0x515b60) at 
> src/zookeeper.c:2100
> #3  0x000000000040220b in main ()
> and the thread which handle the zoo_wget_children(in the default_zoo_watcher) 
> is waiting for sc->cond. 
> (gdb) thread 2
> [Switching to thread 2 (Thread 1094719840 (LWP 25093))]#0  0x000000302b8089aa 
> in pthread_cond_wait@@GLIBC_2.3.2 ()
>    from /lib64/tls/libpthread.so.0
> (gdb) bt
> #0  0x000000302b8089aa in pthread_cond_wait@@GLIBC_2.3.2 () from 
> /lib64/tls/libpthread.so.0
> #1  0x000000000040d88b in wait_sync_completion (sc=0x5167f0) at 
> src/mt_adaptor.c:82
> #2  0x00000000004082c9 in zoo_wget_children (zh=0x515b60, path=0x40ebc0 
> "/mytest", watcher=0x401fd8 <default_zoo_watcher>, watcherCtx=Variable 
> "watcherCtx" is not available.)
>     at src/zookeeper.c:2884
> #3  0x0000000000402037 in default_zoo_watcher ()
> #4  0x000000000040d664 in deliverWatchers (zh=0x515b60, type=4, state=3, 
> path=0x515100 "/mytest", list=0x5177d8) at src/zk_hashtable.c:274
> #5  0x0000000000403861 in process_completions (zh=0x515b60) at 
> src/zookeeper.c:1631
> #6  0x000000000040e1b5 in do_completion (v=Variable "v" is not available.) at 
> src/mt_adaptor.c:333
> #7  0x000000302b80610a in start_thread () from /lib64/tls/libpthread.so.0
> #8  0x000000302afc6003 in clone () from /lib64/tls/libc.so.6
> #9  0x0000000000000000 in ?? ()
> here, a deadlock presents.

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