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   clone    ( 2 )

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Ошибки (баги) (Bugs)

GNU C library versions 2.3.4 up to and including 2.24 contained a
       wrapper function for getpid(2) that performed caching of PIDs.
       This caching relied on support in the glibc wrapper for clone(),
       but limitations in the implementation meant that the cache was
       not up to date in some circumstances.  In particular, if a signal
       was delivered to the child immediately after the clone() call,
       then a call to getpid(2) in a handler for the signal could return
       the PID of the calling process ("the parent"), if the clone
       wrapper had not yet had a chance to update the PID cache in the
       child.  (This discussion ignores the case where the child was
       created using CLONE_THREAD, when getpid(2) should return the same
       value in the child and in the process that called clone(), since
       the caller and the child are in the same thread group.  The
       stale-cache problem also does not occur if the flags argument
       includes CLONE_VM.)  To get the truth, it was sometimes necessary
       to use code such as the following:

           #include <syscall.h>

           pid_t mypid;

           mypid = syscall(SYS_getpid);

       Because of the stale-cache problem, as well as other problems
       noted in getpid(2), the PID caching feature was removed in glibc
       2.25.