问题：
sem_open will failed with "No such file or directory"
解释1：
这是由于在Linux内核中，创建信号量的默认路径是/dev/shm。当你要创建一个信号量/tmp/mysem时，实际上是创建了一个/dev/shm /sem.tmp/mysem，而这里由于/dev/shm/tmp目录根本就不存在，所以会出错。
解决方法：
*直接写信号量文件的名字或宏定义不带路径，将会创建在/dev/shm中：sem_open("mysem", ...)
解释2：
If define name as "/tmp/xxxx", and invoke sem_open(name, flag...), sem_open will failed with "No such file or directory".
Looked into the code sem_open.c, the reason is that the name ("/tmp/xxxx")will map to /dev/shm/sem.tmp/xxxx, but sem.tmp directory is not there, so there will be an error.
I think in sem_open.c, it maybe needs a check of whether name has more slash characters other than the leading slash character.
If it has, mkdir the related directory before rename operation (sem_open.c:234), such as the following:
tmpname = strrchr(finalname,'/');// get the file name without directorystrncpy(pathname, finalname, strlen(finalname)- strlen(tmpname));// get the directory pathmkdir(pathname,0777)
To the POSIX std, it says the interpretation of slash characters other than the leading slash character in name is implementaion defined. I think it will be more friendly to allow the user using a name with directory.