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scoped_ignore_signal: Use sigprocmask+sigtimedwait instead of signal

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The problem with using signal(...) to temporarily ignore a signal, is
that that changes the the signal disposition for the whole process.
If multiple threads do it at the same time, you have a race.

Fix this by using sigprocmask + sigtimedwait to implement the ignoring
instead, if available, which I think probably means everywhere except
Windows nowadays.  This way, we only change the signal mask for the
current thread, so there's no race.

Change-Id: Idfe3fb08327ef8cae926f3de9ee81c56a83b1738

gdbsupport/ChangeLog:
yyyy-mm-dd  Pedro Alves  <pedro@palves.net>

	* scoped_ignore_signal.h
	(scoped_ignore_signal::scoped_ignore_signal)
	[HAVE_SIGPROCMASK]: Use sigprocmask to block the signal instead of
	changing the signal disposition for the whole process.
	(scoped_ignore_signal::~scoped_ignore_signal) [HAVE_SIGPROCMASK]:
	Use sigtimedwait and sigprocmask to flush and unblock the signal.
This commit is contained in:
Pedro Alves
2021-06-17 16:16:55 +01:00
parent 6a7f1c20e8
commit 606a431366
2 changed files with 44 additions and 2 deletions
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9
gdbsupport/ChangeLog
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@@ -1,3 +1,12 @@
2021-06-17 Pedro Alves <pedro@palves.net>
* scoped_ignore_signal.h
(scoped_ignore_signal::scoped_ignore_signal)
[HAVE_SIGPROCMASK]: Use sigprocmask to block the signal instead of
changing the signal disposition for the whole process.
(scoped_ignore_signal::~scoped_ignore_signal) [HAVE_SIGPROCMASK]:
Use sigtimedwait and sigprocmask to flush and unblock the signal.
2021-06-17 Pedro Alves <pedro@palves.net>
* scoped_ignore_sigttou.h: New file, moved from gdb/ and renamed.

37
gdbsupport/scoped_ignore_signal.h
View File

@@ -22,7 +22,10 @@
#include <signal.h>
/* RAII class used to ignore a signal in a scope. */
/* RAII class used to ignore a signal in a scope. If sigprocmask is
supported, then the signal is only ignored by the calling thread.
Otherwise, the signal disposition is set to SIG_IGN, which affects
the whole process. */
template <int Sig>
class scoped_ignore_signal
@@ -30,18 +33,48 @@ class scoped_ignore_signal
public:
scoped_ignore_signal ()
{
#ifdef HAVE_SIGPROCMASK
sigset_t set, old_state;
sigemptyset (&set);
sigaddset (&set, Sig);
sigprocmask (SIG_BLOCK, &set, &old_state);
m_was_blocked = sigismember (&old_state, Sig);
#else
m_osig = signal (Sig, SIG_IGN);
#endif
}
~scoped_ignore_signal ()
{
#ifdef HAVE_SIGPROCMASK
if (!m_was_blocked)
{
sigset_t set;
const timespec zero_timeout = {};
sigemptyset (&set);
sigaddset (&set, Sig);
/* If we got a pending Sig signal, consume it before
unblocking. */
sigtimedwait (&set, nullptr, &zero_timeout);
sigprocmask (SIG_UNBLOCK, &set, nullptr);
}
#else
signal (Sig, m_osig);
#endif
}
DISABLE_COPY_AND_ASSIGN (scoped_ignore_signal);
private:
sighandler_t m_osig = nullptr;
#ifdef HAVE_SIGPROCMASK
bool m_was_blocked;
#else
sighandler_t m_osig;
#endif
};
struct scoped_ignore_signal_nop