The existing function sched::thread::find_by_id() efficiently finds a
sched::thread object given a numerical id. However, if this call races
with the thread's exit, the returned thread pointer may no longer be
valid and using it might result in a crash.
This patch adds a safer function, sched::with_thread_by_id() which runs
a given function on the thread with the given id - while holding a mutex
which prevents threads (including this one) from exiting. Because it holds
this mutex, the function should typically be very short - e.g., test
something about this thread.
Signed-off-by: Nadav Har'El <n...@scylladb.com>
---
include/osv/sched.hh | 12 ++++++++++++
core/sched.cc | 6 ++++++
2 files changed, 18 insertions(+)
diff --git a/include/osv/sched.hh b/include/osv/sched.hh
index f678ba2..3a19247 100644
--- a/include/osv/sched.hh
+++ b/include/osv/sched.hh
@@ -1329,6 +1329,18 @@ inline void migrate_enable()
// this function should be used sparingly, e.g., for debugging.
void with_all_threads(std::function<void(sched::thread &)>);
+// with_thread_by_id(id, f) finds the thread with the given id, and calls
+// the given function f() for it. A pointer to the thread is passed, or a
+// null pointer if a thread with that id does not exist.
+// The implementation is safe, in that it is guaranteed that while f is
+// operating on the thread, the thread object will not be concurrently
+// destroyed.
+// NOTE: The current implementation holds a mutex (thread_map_mutex) during
+// the entire with_thread_by_id() run. This blocks, among other things,
+// thread creation and destruction. For this reason, the given function
+// should return quickly.
+void with_thread_by_id(unsigned id, std::function<void(sched::thread *)>);
+
}
#endif /* SCHED_HH_ */
diff --git a/core/sched.cc b/core/sched.cc
index 306fc8e..7ee1fe2 100644
--- a/core/sched.cc
+++ b/core/sched.cc
@@ -1779,6 +1779,12 @@ void with_all_threads(std::function<void(thread &)> f) {
}
}
+void with_thread_by_id(unsigned id, std::function<void(thread *)> f) {
+ WITH_LOCK(thread_map_mutex) {
+ f(thread::find_by_id(id));
+ }
+}
+
}
--
2.9.3
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