improve parallel cycle tests

Before we could not observe the case where:

* thread A is blocked on B
* cycle detected in thread B
* some participants are on thread A and have to be marked

(In particular, I commented out some code that seemed necessary and
didn't see any tests fail)

tests/parallel/cycles.rs

@@ -6,78 +6,118 @@ use crate::setup::{Knobs, ParDatabase, ParDatabaseImpl};
 use salsa::{Cancelled, ParallelDatabase};
 use test_env_log::test;
 
-pub(crate) fn recover_cycle(_db: &dyn ParDatabase, _cycle: &[String], key: &i32) -> i32 {
-    key * 10
+// Recover cycle test:
+//
+// The pattern is as follows.
+//
+// Thread A                   Thread B
+// --------                   --------
+// a1                         b1
+// |                          wait for stage 1 (blocks)
+// signal stage 1             |
+// wait for stage 2 (blocks)  (unblocked)
+// |                          signal stage 2
+// (unblocked)                wait for stage 3 (blocks)
+// a2                         |
+// b1 (blocks -> stage 3)     |
+// |                          (unblocked)
+// |                          b2
+// |                          a1 (cycle detected, recovers)
+// |                          b2 completes, recovers
+// |                          b1 completes, recovers
+// a2 sees cycle, recovers
+// a1 completes, recovers
+
+pub(crate) fn recover_from_cycle_a1(_db: &dyn ParDatabase, _cycle: &[String], key: &i32) -> i32 {
+    log::debug!("recover_from_cycle_a1");
+    key * 10 + 1
 }
 
-pub(crate) fn recover_cycle_a(db: &dyn ParDatabase, key: i32) -> i32 {
-    // Wait to create the cycle until both threads have entered
-    db.signal(0);
-    db.wait_for(1);
-
-    db.recover_cycle_b(key)
+pub(crate) fn recover_from_cycle_a2(_db: &dyn ParDatabase, _cycle: &[String], key: &i32) -> i32 {
+    log::debug!("recover_from_cycle_a2");
+    key * 10 + 2
 }
 
-pub(crate) fn recover_cycle_b(db: &dyn ParDatabase, key: i32) -> i32 {
+pub(crate) fn recover_from_cycle_b1(_db: &dyn ParDatabase, _cycle: &[String], key: &i32) -> i32 {
+    log::debug!("recover_from_cycle_b1");
+    key * 20 + 1
+}
+
+pub(crate) fn recover_from_cycle_b2(_db: &dyn ParDatabase, _cycle: &[String], key: &i32) -> i32 {
+    log::debug!("recover_from_cycle_b2");
+    key * 20 + 2
+}
+
+pub(crate) fn recover_cycle_a1(db: &dyn ParDatabase, key: i32) -> i32 {
     // Wait to create the cycle until both threads have entered
-    db.wait_for(0);
     db.signal(1);
+    db.wait_for(2);
 
-    if key < 0 && db.should_cycle() {
-        db.recover_cycle_a(key)
-    } else {
-        key
-    }
+    db.recover_cycle_a2(key)
+}
+
+pub(crate) fn recover_cycle_a2(db: &dyn ParDatabase, key: i32) -> i32 {
+    db.recover_cycle_b1(key)
+}
+
+pub(crate) fn recover_cycle_b1(db: &dyn ParDatabase, key: i32) -> i32 {
+    // Wait to create the cycle until both threads have entered
+    db.wait_for(1);
+    db.signal(2);
+
+    // Wait for thread A to block on this thread
+    db.wait_for(3);
+
+    db.recover_cycle_b2(key)
+}
+
+pub(crate) fn recover_cycle_b2(db: &dyn ParDatabase, key: i32) -> i32 {
+    db.recover_cycle_a1(key)
 }
 
 pub(crate) fn panic_cycle_a(db: &dyn ParDatabase, key: i32) -> i32 {
     // Wait to create the cycle until both threads have entered
-    db.signal(0);
-    db.wait_for(1);
+    db.signal(1);
+    db.wait_for(2);
 
     db.panic_cycle_b(key)
 }
 
 pub(crate) fn panic_cycle_b(db: &dyn ParDatabase, key: i32) -> i32 {
     // Wait to create the cycle until both threads have entered
-    db.wait_for(0);
-    db.signal(1);
+    db.wait_for(1);
+    db.signal(2);
 
     // Wait for thread A to block on this thread
-    db.wait_for(2);
+    db.wait_for(3);
 
     // Now try to execute A
-    if key < 0 && db.should_cycle() {
     db.panic_cycle_a(key)
-    } else {
-        key
-    }
 }
 
 #[test]
 fn recover_parallel_cycle() {
     let mut db = ParDatabaseImpl::default();
-    db.set_should_cycle(true);
+    db.knobs().signal_on_will_block.set(3);
 
     let thread_a = std::thread::spawn({
         let db = db.snapshot();
-        move || db.recover_cycle_a(-1)
+        move || db.recover_cycle_a1(1)
     });
 
     let thread_b = std::thread::spawn({
         let db = db.snapshot();
-        move || db.recover_cycle_b(-1)
+        move || db.recover_cycle_b1(1)
     });
 
-    assert_eq!(thread_a.join().unwrap(), -10);
-    assert_eq!(thread_b.join().unwrap(), -10);
+    assert_eq!(thread_a.join().unwrap(), 11);
+    assert_eq!(thread_b.join().unwrap(), 21);
 }
 
 #[test]
 fn panic_parallel_cycle() {
     let mut db = ParDatabaseImpl::default();
-    db.set_should_cycle(true);
-    db.knobs().signal_on_will_block.set(2);
+    db.knobs().signal_on_will_block.set(3);
 
     let thread_a = std::thread::spawn({
         let db = db.snapshot();

tests/parallel/setup.rs

@@ -27,23 +27,21 @@ pub(crate) trait ParDatabase: Knobs {
     /// Invokes `sum2_drop_sum`
     fn sum3_drop_sum(&self, key: &'static str) -> usize;
 
-    // Cycle tests:
-    //
-    // A ───────► B
-    //
-    // ▲          │
-    // └──────────┘
-    //  if key > 0
-    //  && should_cycle
+    #[salsa::cycle(crate::cycles::recover_from_cycle_a1)]
+    #[salsa::invoke(crate::cycles::recover_cycle_a1)]
+    fn recover_cycle_a1(&self, key: i32) -> i32;
 
-    #[salsa::input]
-    fn should_cycle(&self) -> bool;
-    #[salsa::cycle(crate::cycles::recover_cycle)]
-    #[salsa::invoke(crate::cycles::recover_cycle_a)]
-    fn recover_cycle_a(&self, key: i32) -> i32;
-    #[salsa::cycle(crate::cycles::recover_cycle)]
-    #[salsa::invoke(crate::cycles::recover_cycle_b)]
-    fn recover_cycle_b(&self, key: i32) -> i32;
+    #[salsa::cycle(crate::cycles::recover_from_cycle_a2)]
+    #[salsa::invoke(crate::cycles::recover_cycle_a2)]
+    fn recover_cycle_a2(&self, key: i32) -> i32;
+
+    #[salsa::cycle(crate::cycles::recover_from_cycle_b1)]
+    #[salsa::invoke(crate::cycles::recover_cycle_b1)]
+    fn recover_cycle_b1(&self, key: i32) -> i32;
+
+    #[salsa::cycle(crate::cycles::recover_from_cycle_b2)]
+    #[salsa::invoke(crate::cycles::recover_cycle_b2)]
+    fn recover_cycle_b2(&self, key: i32) -> i32;
 
     #[salsa::invoke(crate::cycles::panic_cycle_a)]
     fn panic_cycle_a(&self, key: i32) -> i32;