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main: add support for pause (SIGUSR1) and resume (SIGUSR2)

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These are simple on/off switches for the task queue.  They are lightweight
requests for bees to be paused temporarily, but allow bees to release
open files and save progress while paused.

These signals are an alternative to SIGSTOP and SIGCONT, or using the
cgroup freezer's FROZEN and THAWED states, which pause and resume the
bees process, but do not allow the bees process to release open files
or save progress.  Snapshot and file deletes can occur on the filesystem
while bees is paused by SIGUSR1 but not by SIGSTOP.

These signals are also an alternative to SIGTERM and restart, which
flush out the whole hash table and progress state on exit, and read
the whole table back into memory on restart.

This feature is experimental and may be replaced by a more general
configuration or runtime control mechanism in the future.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This commit is contained in:
Zygo Blaxell 2024-12-12 22:53:56 -05:00
parent 1cbc894e6f
commit 0580c10082
1 changed files with 26 additions and 8 deletions
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34
src/bees.cc
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@ -574,19 +574,23 @@ operator<<(ostream &os, const siginfo_t &si)
static sigset_t new_sigset, old_sigset;
static
void
block_term_signal()
block_signals()
{
BEESLOGDEBUG("Masking signals");
DIE_IF_NON_ZERO(sigemptyset(&new_sigset));
DIE_IF_NON_ZERO(sigaddset(&new_sigset, SIGTERM));
DIE_IF_NON_ZERO(sigaddset(&new_sigset, SIGINT));
DIE_IF_NON_ZERO(sigaddset(&new_sigset, SIGUSR1));
DIE_IF_NON_ZERO(sigaddset(&new_sigset, SIGUSR2));
DIE_IF_NON_ZERO(sigprocmask(SIG_BLOCK, &new_sigset, &old_sigset));
}
static
void
wait_for_term_signal()
wait_for_signals()
{
BEESNOTE("waiting for signals");
BEESLOGDEBUG("Waiting for signals...");
@ -603,14 +607,28 @@ wait_for_term_signal()
THROW_ERRNO("sigwaitinfo errno = " << errno);
} else {
BEESLOGNOTICE("Received signal " << rv << " info " << info);
// Unblock so we die immediately if signalled again
DIE_IF_NON_ZERO(sigprocmask(SIG_BLOCK, &old_sigset, &new_sigset));
break;
// If SIGTERM or SIGINT, unblock so we die immediately if signalled again
switch (info.si_signo) {
case SIGUSR1:
BEESLOGNOTICE("Received SIGUSR1 - pausing workers");
TaskMaster::pause(true);
break;
case SIGUSR2:
BEESLOGNOTICE("Received SIGUSR2 - unpausing workers");
TaskMaster::pause(false);
break;
case SIGTERM:
case SIGINT:
default:
DIE_IF_NON_ZERO(sigprocmask(SIG_BLOCK, &old_sigset, &new_sigset));
BEESLOGDEBUG("Signal catcher exiting");
return;
}
}
}
BEESLOGDEBUG("Signal catcher exiting");
}
static
int
bees_main(int argc, char *argv[])
{
@ -634,7 +652,7 @@ bees_main(int argc, char *argv[])
// Have to block signals now before we create a bunch of threads
// so the threads will also have the signals blocked.
block_term_signal();
block_signals();
// Create a context so we can apply configuration to it
shared_ptr<BeesContext> bc = make_shared<BeesContext>();
@ -808,7 +826,7 @@ bees_main(int argc, char *argv[])
bc->start();
// Now we just wait forever
wait_for_term_signal();
wait_for_signals();
// Shut it down
bc->stop();