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Restore SIGPIPE default action before exec(3)

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Python chooses to ignore SIGPIPE, however most unix processes expect
to terminate on the signal.  Therefore failing to restore the default
action results in surprising behavior.  For example, we expect
`dd if=/dev/zero | head -c1` to return immediately.  However, prior to
this commit, that pipeline would hang forever.  Insidious forms of
data corruption or loss were also possible.

See:

  http://www.chiark.greenend.org.uk/ucgi/~cjwatson/blosxom/2009-07-02-python-sigpipe.html
  http://blog.nelhage.com/2010/02/a-very-subtle-bug/
This commit is contained in:
Travis Cross 2013-06-28 01:48:41 +00:00 • committed by Avery Pennarun
commit cb713bdace
1 changed files with 3 additions and 1 deletions
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4
builder.py
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@ -1,4 +1,4 @@
import sys, os, errno, stat import sys, os, errno, stat, signal
import vars, jwack, state import vars, jwack, state
from helpers import unlink, close_on_exec, join from helpers import unlink, close_on_exec, join
from log import log, log_, debug, debug2, err, warn from log import log, log_, debug, debug2, err, warn
@ -190,6 +190,7 @@ class BuildJob:
def run(): def run():
os.chdir(vars.BASE) os.chdir(vars.BASE)
os.environ['REDO_DEPTH'] = vars.DEPTH + ' ' os.environ['REDO_DEPTH'] = vars.DEPTH + ' '
signal.signal(signal.SIGPIPE, signal.SIG_DFL) # python ignores SIGPIPE
os.execvp(argv[0], argv) os.execvp(argv[0], argv)
assert(0) assert(0)
# returns only if there's an exception # returns only if there's an exception
@ -214,6 +215,7 @@ class BuildJob:
os.dup2(self.f.fileno(), 1) os.dup2(self.f.fileno(), 1)
os.close(self.f.fileno()) os.close(self.f.fileno())
close_on_exec(1, False) close_on_exec(1, False)
signal.signal(signal.SIGPIPE, signal.SIG_DFL) # python ignores SIGPIPE
if vars.VERBOSE or vars.XTRACE: log_('* %s\n' % ' '.join(self.argv)) if vars.VERBOSE or vars.XTRACE: log_('* %s\n' % ' '.join(self.argv))
os.execvp(self.argv[0], self.argv) os.execvp(self.argv[0], self.argv)
assert(0) assert(0)