Various bugfixes and cleanups in the support for federated programs #323
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Prevent exiting via SIGPIPE on socket write failure and instead handle the error. Distinguish normal termination from interrupted termination and avoid mutexes in the latter and avoid lf_print in the former. Remove unnecessary absent messages using EIMT and EIMT_strict. Eliminate the bogus port search algorithm (which never worked) and just use DEFAULT_PORT or an override given on the command line or an `at` clause. Also, calloc instead of malloc federate info so that pointers are reliably NULL. Also, added lf_print_error_system_failure utility to print system call error information.
Distinguish normal termination from interrupted termination and avoid mutexes in the latter and avoid lf_print in the former. Remove unnecessary absent messages using EIMT and EIMT_strict. Eliminate the bogus port search algorithm (which never worked) and just use DEFAULT_PORT or an override given on the command line or an `at` clause. Replace last_time field on a trigger with last_tag. Also, implement and use lf_print_error_system_failure to report system call errors.
lhstrh
approved these changes
Dec 21, 2023
* Federate sends NEVER_TAG in RESIGN to indicate error and RTI returns an error code. * RTI reads the tag on the RESIGN message always, not just if tracing is enabled. * Avoid attempting to close stdin, which results from faulty initialization of array. * More systematic socket shutdown process that ensures acknowledgements are received.
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Is clock synchronization broken in this branch? It looks like here it is assumed that the return value of |
My bad. I've pushed a fix. Thanks for spotting this. Not sure how I missed it. |
Co-authored-by: Peter Donovan <33707478+petervdonovan@users.noreply.github.com>
Co-authored-by: Peter Donovan <33707478+petervdonovan@users.noreply.github.com>
Co-authored-by: Peter Donovan <33707478+petervdonovan@users.noreply.github.com>
petervdonovan
approved these changes
Jan 18, 2024
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This replaces PR #319 and #317 with a cleaner commit history. There is a companion PR in lingua-franca.
This PR removes absent messages except where they are absolutely needed, namely in zero-delay cycles.
This PR also improves the port search done by the RTI if it cannot bind to the specified or default port. This previously did not work and resulted in federates taking a long time to fail as they searched over possible ports.
This PR also fixes two issues that can cause the RTI to deadlock during shutdown, particularly if a task is kill with a SIGINT during execution. Both of these issues had been previously found by @erlingrj, but fixed only the federate side, not on the RTI side.
The first is that if a write to a socket fails because of a broken pipe, a SIGPIPE signal is issued, and, by default, the process is terminated. The reason for this is that a common use of sockets is to pipe one process's output to another, e.g.
foo | bar, and if the second process crashes, you want the first process to exit. However, in the RTI (and the federates), there is a mutex lock that is held when writing to an outgoing socket (to prevent multiple threads from writing simultaneously to the socket). So, what can happen is that the process acquires the mutex and calls write(), but then write() fails, and before it can be return, a registered termination function is called. That termination function tries to acquire the same mutex in order to close the sockets. The result is a deadlock.The second problem is similar, but only occurs if tracing is turned on. When a process exits the termination function tries to acquire a lock to flush tracing output, but that lock may be held by a thread that has exited anomalously while in a critical section.
It is possible that either of these problems could cause CI tests to hang rather than time out. When they time out, the CI tools try to kill the process with a SIGINT, and hence could trigger one of the above deadlocks, thereby failing to kill the process. The CI job will then run for the full six hours before being cancelled.
This PR also simplifies what is done when an abnormal termination occurs, e.g. SIGINT. In particular, it avoids acquiring any mutex locks and does not bother freeing memory (the memory will be freed by the OS anyway). The reason for freeing memory on normal termination is so that valgrind or similar tools can be used to check for memory leaks, but checking for memory leaks in a program that gets terminated with Control-C is not reasonable.
This PR also fixes some problems that could occur when safe-to-process violations occur and, in case problem resurface in the future, causes the program to error out rather than to deadlock.