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From 4c5fdbde7e745126f31542a70b45cc4faec094d2 Mon Sep 17 00:00:00 2001
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From: Lennart Poettering <lennart@poettering.net>
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Date: Wed, 30 Oct 2019 20:26:50 +0100
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Subject: [PATCH] sd-event: refuse running default event loops in any other
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 thread than the one they are default for
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(cherry picked from commit e544601536ac13a288d7476f4400c7b0f22b7ea1)
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Related: #1819868
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---
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 TODO                               | 1 -
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 src/libsystemd/sd-event/sd-event.c | 5 +++++
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 2 files changed, 5 insertions(+), 1 deletion(-)
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diff --git a/TODO b/TODO
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index 8f78000089..3100e067d6 100644
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--- a/TODO
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+++ b/TODO
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@@ -581,7 +581,6 @@ Features:
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   - allow multiple signal handlers per signal?
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   - document chaining of signal handler for SIGCHLD and child handlers
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   - define more intervals where we will shift wakeup intervals around in, 1h, 6h, 24h, ...
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-  - generate a failure of a default event loop is executed out-of-thread
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   - maybe add support for inotify events (which we can do safely now, with O_PATH)
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 * investigate endianness issues of UUID vs. GUID
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diff --git a/src/libsystemd/sd-event/sd-event.c b/src/libsystemd/sd-event/sd-event.c
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index 88641879cc..537a0b81d4 100644
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--- a/src/libsystemd/sd-event/sd-event.c
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+++ b/src/libsystemd/sd-event/sd-event.c
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@@ -3360,6 +3360,11 @@ _public_ int sd_event_prepare(sd_event *e) {
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         assert_return(e->state != SD_EVENT_FINISHED, -ESTALE);
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         assert_return(e->state == SD_EVENT_INITIAL, -EBUSY);
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+        /* Let's check that if we are a default event loop we are executed in the correct thread. We only do
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+         * this check here once, since gettid() is typically not cached, and thus want to minimize
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+         * syscalls */
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+        assert_return(!e->default_event_ptr || e->tid == gettid(), -EREMOTEIO);
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+
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         if (e->exit_requested)
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                 goto pending;
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