This commit removes an erroneous "if sbyfile" that would turn '-f' into a no-op
for stdin input files. Presumably this check was originally intended to handle
the case of stdin input file and no specified workdir (which uses a temporary
workdir). In the current version the check is redundant for this particular
case. The check is erroneous in the case of stdin input file and a specified
workdir, so we simply remove the check.
The old test tried to find two primes that are 7 apart. It is supposed to time
out after 1 second but on newer hardware the test completes too quickly. This
commit replaces it with a new test that tries to find a non-trivial solution to
the diophantine equation a**3 + b**3 == c**3, which is a lot more difficult.
ABC will sometimes return negative frame numbers when proving by convergence, e.g.
```
engine_0: Proved output 1 in frame -698905656 (converged).
engine_0: Proved output 4 in frame -698905656 (converged).
```
This change fixes these properties being missed and causing the engine status to return UNKNOWN due to `proved_count != len(proved)`.
This adds initial support for an sqlite database that is shared across
multiple tasks of a single SBY file and that can track the status of
individual properties.
The amount of information tracked in the database is currently quite
minimal and depends on the engine and options used. This can be
incrementally extended in the future.
The ways in which the information in the database can be queries is even
more limited for this initial version, consisting of a single '--status'
option which lists all properties and their status.
When multiple SBY processes run in parallel (from a Makefile or other
job-server aware tool) and each SBY process runs tasks in parallel, each
with enough tasks to be limited by the total job count, it is possible
for the processes to race in such a way that every SBY process's helper
process is in a blocking read from the job-server but a job-token would
only become available as soon as any SBY process exits.
In that situation SBY doesn't actually need the job-token anymore and
only previously requested it as there was opportunity for parallelism.
It would immediatly return the token as soon as it is acquired. That's
usually sufficient to deal with no-longer-needed-but-requested tokens,
but when SBY is done, it needs to return the job-token held by the
parent process ASAP which it can only do by actually exiting, so we need
to interrupt the blocking read of SBY's helper process.
This could be done by sending a signal to the helper process, except
that Python made the decision in 3.5 to have automatic EINTR retry loops
around most system calls with no opt-out. That was part of the reason to
go with this specifc helper process design that avoids interrupting a
blocking read in the first place.
Using an exception raised from the signal handler instead might lose a
token when the signal arrives after the read returns, but before the
token is stored in a variable. You cannot recover from a lost token in
the context of the job-server protocol, so that's not an option. (This
can't happen with recent Python versions but that would depend on
undocumented behavior that could plausibly change again.)
Thankfully the only case where we need to interrupt the read is when SBY
is about to exit and will not request any further tokens. This allows us
to use a signal handler that uses dup2 to close and replace the
read-from fd with one that already is at EOF, making the next retry
return immediatly. (If we'd need to interrupt a read and continue
running we could also do this but the fd shuffling would be more
involved.)
