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base: tolerate nested signal handling (but warn)

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This commit is contained in:
Norman Feske 2017-02-15 11:24:43 +01:00
parent b66716d278
commit 8e6306e8e3
1 changed files with 30 additions and 2 deletions
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32
repos/base/src/lib/base/signal_common.cc
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@ -77,8 +77,36 @@ void Signal::_inc_ref()
Signal::Signal(Signal::Data data) : _data(data)
{
if (_data.context) {
_data.context->_ref_cnt = 1;
_data.context->_destroy_lock.lock();
_data.context->_ref_cnt++;
/*
* Defer the destruction of the context until the handling of the
* 'Signal' has completed.
*
* Normally, the context can only have one 'Signal' in flight, which is
* destroyed before 'pending_signal' is called the next time. However,
* one exception is a signal handler that unexpectedly calls
* 'pending_signal' itself (i.e., via 'wait_and_dispatch_one_signal').
* As this is dangerous programming pattern (that should be fixed), we
* print a warning.
*
* In this situation, the context-destroy lock is already taken by the
* outer scope. To avoid a deadlock during the attempt to create
* a second 'Signal' object for the same context, we take the lock
* only in the outer scope (where the context's reference counter
* is in its clear state).
*/
if (_data.context->_ref_cnt == 1) {
_data.context->_destroy_lock.lock();
} else {
/* print warning only once to avoid flooding the log */
static bool printed;
if (!printed) {
warning("attempt to handle the same signal context twice (nested)");
printed = true;
}
}
}
}