sem_open中信號量命名

問題：

sem_open will failed with "No such file or directory"

 

解釋1：

這是由於在Linux內核中，創建信號量的默認路徑是/dev/shm。當你要創建一個信號量/tmp/mysem時，實際上是創建了一個/dev/shm /sem.tmp/mysem，而這里由於/dev/shm/tmp目錄根本就不存在，所以會出錯。

解決方法：

    *直接寫信號量文件的名字或宏定義不帶路徑，將會創建在/dev/shm中：sem_open("mysem", ...) 

 

解釋2：

http://listman.redhat.com/archives/phil-list/2003-January/msg00113.html

 

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:

1. tmpname = strrchr(finalname,'/');// get the file name without directory
2. strncpy(pathname, finalname, strlen(finalname)- strlen(tmpname));// get the directory path
3. mkdir(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.

來自為知筆記(Wiz)