IPC Semaphore

getpid()                                = 807667
eventfd2(2, EFD_SEMAPHORE|EFD_NONBLOCK) = 7
getpid()                                = 807667
pidfd_open(807667, 0)                   = 8
pidfd_getfd(8, 7, 0)                    = 9
close(8)                                = 0
getpid()                                = 807667
read(9, "\1\0\0\0\0\0\0\0", 8)          = 8
read(7, "\1\0\0\0\0\0\0\0", 8)          = 8
read(9, 0x7ffcccc51f30, 8)              = -1 EAGAIN (Resource temporarily unavailable)
read(7, 0x7ffcccc51f30, 8)              = -1 EAGAIN (Resource temporarily unavailable)
write(7, "\1\0\0\0\0\0\0\0", 8)         = 8
read(7, "\1\0\0\0\0\0\0\0", 8)          = 8
read(9, 0x7ffcccc51f30, 8)              = -1 EAGAIN (Resource temporarily unavailable)
read(7, 0x7ffcccc51f30, 8)              = -1 EAGAIN (Resource temporarily unavailable)
getpid()                                = 807667
close(9)                                = 0
getpid()                                = 807667
close(7)                                = 0