On Sat, 24 Mar 2018 04:43:42 -0400, Jeffrey Walton said:
My question is, is a futex with a 2147483647 or -1 expected? Where should I be looking to begin to narrow the problem down?
'man 7 futex' says: Semantics Any futex operation starts in user space, but it may be necessary to communicate with the kernel using the futex(2) system call. To "up" a futex, execute the proper assembler instructions that will cause the host CPU to atomically increment the integer. Afterward, check if it has in fact changed from 0 to 1, in which case there were no waiters and the operation is done. This is the noncontended case which is fast and should be common. In the contended case, the atomic increment changed the counter from -1 (or some other negative number). If this is detected, there are wait- ers. User space should now set the counter to 1 and instruct the ker- nel to wake up any waiters using the FUTEX_WAKE operation. Waiting on a futex, to "down" it, is the reverse operation. Atomically decrement the counter and check if it changed to 0, in which case the operation is done and the futex was uncontended. In all other circum- stances, the process should set the counter to -1 and request that the kernel wait for another process to up the futex. This is done using the FUTEX_WAIT operation. The futex(2) system call can optionally be passed a timeout specifying how long the kernel should wait for the futex to be upped. In this case, semantics are more complex and the programmer is referred to futex(2) for more details. The same holds for asynchronous futex waiting. which pretty much says that a negative value means there's somebody waiting on the futex.