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author | Rich Felker <dalias@aerifal.cx> | 2020-05-22 17:45:47 -0400 |
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committer | Rich Felker <dalias@aerifal.cx> | 2020-05-22 17:45:47 -0400 |
commit | 8d81ba8c0bc6fe31136cb15c9c82ef4c24965040 (patch) | |
tree | 356aea3c8d201c577158b163eace2e0014e03fed /src/thread/__lock.c | |
parent | f12888e9eb9eed60cc266b899dcafecb4752964a (diff) | |
download | musl-8d81ba8c0bc6fe31136cb15c9c82ef4c24965040.tar.gz |
restore lock-skipping for processes that return to single-threaded state
the design used here relies on the barrier provided by the first lock
operation after the process returns to single-threaded state to
synchronize with actions by the last thread that exited. by storing
the intent to change modes in the same object used to detect whether
locking is needed, it's possible to avoid an extra (possibly costly)
memory load after the lock is taken.
Diffstat (limited to 'src/thread/__lock.c')
-rw-r--r-- | src/thread/__lock.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/src/thread/__lock.c b/src/thread/__lock.c index 5b9b144e..60eece49 100644 --- a/src/thread/__lock.c +++ b/src/thread/__lock.c @@ -18,9 +18,11 @@ void __lock(volatile int *l) { - if (!libc.threaded) return; + int need_locks = libc.need_locks; + if (!need_locks) return; /* fast path: INT_MIN for the lock, +1 for the congestion */ int current = a_cas(l, 0, INT_MIN + 1); + if (need_locks < 0) libc.need_locks = 0; if (!current) return; /* A first spin loop, for medium congestion. */ for (unsigned i = 0; i < 10; ++i) { |