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remove unnecessary upgradable_read

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This commit is contained in:
Niko Matsakis 2018-10-30 10:46:53 -04:00
parent 79e24cfa55
commit 7cfcbd73b8
1 changed files with 10 additions and 15 deletions
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25
src/runtime.rs
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@ -1,7 +1,7 @@
use crate::{Database, SweepStrategy};
use lock_api::RawRwLock;
use log::debug;
use parking_lot::{Mutex, RwLock, RwLockReadGuard, RwLockUpgradableReadGuard};
use parking_lot::{Mutex, RwLock, RwLockReadGuard};
use rustc_hash::{FxHashMap, FxHasher};
use smallvec::SmallVec;
use std::cell::RefCell;
@ -190,12 +190,8 @@ where
panic!("increment_revision invoked during a query computation");
}
// Get an (upgradable) read lock, so that we are sure nobody
// else is changing the current revision.
let lock = self.shared_state.query_lock.upgradable_read();
// Flag current revision as cancelled.
// `increment_revision` calls, they may all set the
// Signal that we have a pending increment so that workers can
// start to cancel work.
let old_pending_revision_increments = self
.shared_state
.pending_revision_increments
@ -206,15 +202,14 @@ where
);
// To modify the revision, we need the lock.
let _lock = RwLockUpgradableReadGuard::upgrade(lock);
let _lock = self.shared_state.query_lock.write();
// *Before* updating the revision number, reset
// `revision_cancelled` to false. This way, if anybody should
// happen to invoke `is_current_revision_canceled` before we
// update the number, they don't get an incorrect result (but
// note that, because we hold `query_lock`, no queries can
// be currently executing anyhow, so it's sort of a moot
// point).
// *Before* updating the revision number, decrement the
// `pending_revision_increments` counter. This way, if anybody
// should happen to invoke `is_current_revision_canceled`
// before we update the number, and they read 0, they don't
// get an incorrect result -- once they acquire the query
// lock, we'll be in the new revision.
self.shared_state
.pending_revision_increments
.fetch_sub(1, Ordering::SeqCst);