diff --git a/crates/blockifier/src/concurrency/scheduler.rs b/crates/blockifier/src/concurrency/scheduler.rs
index 6ed5e65817..4a93c5e62c 100644
--- a/crates/blockifier/src/concurrency/scheduler.rs
+++ b/crates/blockifier/src/concurrency/scheduler.rs
@@ -1,6 +1,6 @@
 use std::cmp::min;
 use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
-use std::sync::Mutex;
+use std::sync::{Mutex, MutexGuard};
 
 use crate::concurrency::TxIndex;
 
@@ -20,6 +20,7 @@ pub struct Scheduler {
     decrease_counter: AtomicUsize,
     n_active_tasks: AtomicUsize,
     chunk_size: usize,
+    // TODO(Avi, 15/05/2024): Consider using RwLock instead of Mutex.
     tx_statuses: Box<[Mutex<TransactionStatus>]>,
     /// Updated by the `check_done` procedure, providing a cheap way for all threads to exit their
     /// main loops.
@@ -68,6 +69,16 @@ impl Scheduler {
         assert!(previous_n_active_tasks > 0, "n_active_tasks underflow");
     }
 
+    fn lock_tx_status(&self, tx_index: TxIndex) -> MutexGuard<'_, TransactionStatus> {
+        self.tx_statuses[tx_index].lock().unwrap_or_else(|error| {
+            panic!(
+                "Status of transaction index {} is poisoned. Data: {:?}.",
+                tx_index,
+                *error.get_ref()
+            )
+        })
+    }
+
     pub fn next_task(&self) -> Task {
         if self.done() {
             return Task::Done;
@@ -128,8 +139,11 @@ impl Scheduler {
     /// Updates a transaction's status to `Executing` if it is ready to execute.
     fn try_incarnate(&self, tx_index: TxIndex) -> Option<TxIndex> {
         if tx_index < self.chunk_size {
-            // TODO(barak, 01/04/2024): complete try_incarnate logic.
-            return Some(tx_index);
+            let mut status = self.lock_tx_status(tx_index);
+            if *status == TransactionStatus::ReadyToExecute {
+                *status = TransactionStatus::Executing;
+                return Some(tx_index);
+            }
         }
         self.safe_decrement_n_active_tasks();
         None
@@ -144,8 +158,10 @@ impl Scheduler {
         self.n_active_tasks.fetch_add(1, Ordering::SeqCst);
         let index_to_validate = self.validation_index.fetch_add(1, Ordering::SeqCst);
         if index_to_validate < self.chunk_size {
-            // TODO(barak, 01/04/2024): complete next_version_to_validate logic.
-            return Some(index_to_validate);
+            let status = self.lock_tx_status(index_to_validate);
+            if *status == TransactionStatus::Executed {
+                return Some(index_to_validate);
+            }
         }
         self.safe_decrement_n_active_tasks();
         None
@@ -161,6 +177,14 @@ impl Scheduler {
         let index_to_execute = self.execution_index.fetch_add(1, Ordering::SeqCst);
         self.try_incarnate(index_to_execute)
     }
+
+    #[cfg(test)]
+    fn set_tx_status(&self, tx_index: TxIndex, status: TransactionStatus) {
+        if tx_index < self.chunk_size {
+            let mut tx_status = self.lock_tx_status(tx_index);
+            *tx_status = status;
+        }
+    }
 }
 
 #[derive(Debug, PartialEq)]
diff --git a/crates/blockifier/src/concurrency/scheduler_test.rs b/crates/blockifier/src/concurrency/scheduler_test.rs
index d821c361b0..77510cc0ae 100644
--- a/crates/blockifier/src/concurrency/scheduler_test.rs
+++ b/crates/blockifier/src/concurrency/scheduler_test.rs
@@ -1,5 +1,6 @@
 use std::cmp::min;
 use std::sync::atomic::Ordering;
+use std::sync::Arc;
 
 use pretty_assertions::assert_eq;
 use rstest::rstest;
@@ -31,8 +32,8 @@ fn test_new(#[values(0, 1, 32)] chunk_size: usize) {
 #[case::execution_incomplete(DEFAULT_CHUNK_SIZE-1, DEFAULT_CHUNK_SIZE+1, 0, false)]
 #[case::validation_incomplete(DEFAULT_CHUNK_SIZE, DEFAULT_CHUNK_SIZE-1, 0, false)]
 fn test_check_done(
-    #[case] execution_index: usize,
-    #[case] validation_index: usize,
+    #[case] execution_index: TxIndex,
+    #[case] validation_index: TxIndex,
     #[case] n_active_tasks: usize,
     #[case] expected: bool,
 ) {
@@ -47,119 +48,174 @@ fn test_check_done(
 }
 
 #[rstest]
-#[case::happy_flow(1, 0)]
+#[case::no_panic(1)]
 #[should_panic(expected = "n_active_tasks underflow")]
-#[case::underflow(0, 0)]
-fn test_safe_decrement_n_active_tasks(
-    #[case] n_active_tasks: usize,
-    #[case] expected_n_active_tasks: usize,
-) {
+#[case::underflow_panic(0)]
+fn test_safe_decrement_n_active_tasks(#[case] n_active_tasks: usize) {
     let scheduler =
         default_scheduler!(chunk_size: DEFAULT_CHUNK_SIZE, n_active_tasks: n_active_tasks);
     scheduler.safe_decrement_n_active_tasks();
-    assert_eq!(scheduler.n_active_tasks.load(Ordering::Acquire), expected_n_active_tasks);
+    assert_eq!(scheduler.n_active_tasks.load(Ordering::Acquire), n_active_tasks - 1);
 }
 
 #[rstest]
-#[case::done(DEFAULT_CHUNK_SIZE, DEFAULT_CHUNK_SIZE, true, Task::Done, 0)]
-#[case::no_task(DEFAULT_CHUNK_SIZE, DEFAULT_CHUNK_SIZE, false, Task::NoTask, 0)]
-#[case::execution_task(0, 0, false, Task::ExecutionTask(0), 1)]
-#[case::validation_task(1, 0, false, Task::ValidationTask(0), 1)]
+fn test_lock_tx_status() {
+    let scheduler = Scheduler::new(DEFAULT_CHUNK_SIZE);
+    let status = scheduler.lock_tx_status(0);
+    assert_eq!(*status, TransactionStatus::ReadyToExecute);
+}
+
+#[rstest]
+#[should_panic(expected = "Status of transaction index 0 is poisoned. Data: ReadyToExecute.")]
+fn test_lock_tx_status_poisoned() {
+    let scheduler = Arc::new(Scheduler::new(DEFAULT_CHUNK_SIZE));
+    let scheduler_clone = scheduler.clone();
+    let handle = std::thread::spawn(move || {
+        let _guard = scheduler_clone.lock_tx_status(0);
+        panic!("Intentional panic to poison the mutex")
+    });
+    handle.join().expect_err("Thread did not panic as expected");
+    // The panic is expected here.
+    let _guard = scheduler.lock_tx_status(0);
+}
+
+#[rstest]
+#[case::done(DEFAULT_CHUNK_SIZE, DEFAULT_CHUNK_SIZE, TransactionStatus::Executed, Task::Done)]
+#[case::no_task(DEFAULT_CHUNK_SIZE, DEFAULT_CHUNK_SIZE, TransactionStatus::Executed, Task::NoTask)]
+#[case::no_task_as_validation_index_not_executed(
+    DEFAULT_CHUNK_SIZE,
+    0,
+    TransactionStatus::ReadyToExecute,
+    Task::NoTask
+)]
+#[case::execution_task(0, 0, TransactionStatus::ReadyToExecute, Task::ExecutionTask(0))]
+#[case::execution_task_as_validation_index_not_executed(
+    1,
+    0,
+    TransactionStatus::ReadyToExecute,
+    Task::ExecutionTask(1)
+)]
+#[case::validation_task(1, 0, TransactionStatus::Executed, Task::ValidationTask(0))]
 fn test_next_task(
-    #[case] execution_index: usize,
-    #[case] validation_index: usize,
-    #[case] done_marker: bool,
+    #[case] execution_index: TxIndex,
+    #[case] validation_index: TxIndex,
+    #[case] validation_index_status: TransactionStatus,
     #[case] expected_next_task: Task,
-    #[case] expected_n_active_tasks: usize,
 ) {
     let scheduler = default_scheduler!(
         chunk_size: DEFAULT_CHUNK_SIZE,
         execution_index: execution_index,
         validation_index: validation_index,
-        done_marker: done_marker,
+        done_marker: expected_next_task == Task::Done,
     );
+    scheduler.set_tx_status(validation_index, validation_index_status);
     let next_task = scheduler.next_task();
     assert_eq!(next_task, expected_next_task);
+    let expected_n_active_tasks = match expected_next_task {
+        Task::Done | Task::NoTask => 0,
+        _ => 1,
+    };
     assert_eq!(scheduler.n_active_tasks.load(Ordering::Acquire), expected_n_active_tasks);
 }
 
 #[rstest]
-#[case::target_index_lt_validation_index(1, 3, 1)]
-#[case::target_index_eq_validation_index(3, 3, 0)]
-#[case::target_index_eq_validation_index_eq_zero(0, 0, 0)]
-#[case::target_index_gt_validation_index(1, 0, 0)]
+#[case::target_index_lt_validation_index(1, 3)]
+#[case::target_index_eq_validation_index(3, 3)]
+#[case::target_index_eq_validation_index_eq_zero(0, 0)]
+#[case::target_index_gt_validation_index(1, 0)]
 fn test_decrease_validation_index(
     #[case] target_index: TxIndex,
-    #[case] validation_index: usize,
-    #[case] expected_decrease_counter: usize,
+    #[case] validation_index: TxIndex,
 ) {
     let scheduler =
         default_scheduler!(chunk_size: DEFAULT_CHUNK_SIZE, validation_index: validation_index);
     scheduler.decrease_validation_index(target_index);
     let expected_validation_index = min(target_index, validation_index);
     assert_eq!(scheduler.validation_index.load(Ordering::Acquire), expected_validation_index);
+    let expected_decrease_counter = if target_index < validation_index { 1 } else { 0 };
     assert_eq!(scheduler.decrease_counter.load(Ordering::Acquire), expected_decrease_counter);
 }
 
 #[rstest]
-#[case::target_index_lt_execution_index(1, 3, 1)]
-#[case::target_index_eq_execution_index(3, 3, 0)]
-#[case::target_index_eq_execution_index_eq_zero(0, 0, 0)]
-#[case::target_index_gt_execution_index(1, 0, 0)]
-fn test_decrease_execution_index(
-    #[case] target_index: TxIndex,
-    #[case] execution_index: usize,
-    #[case] expected_decrease_counter: usize,
-) {
+#[case::target_index_lt_execution_index(1, 3)]
+#[case::target_index_eq_execution_index(3, 3)]
+#[case::target_index_eq_execution_index_eq_zero(0, 0)]
+#[case::target_index_gt_execution_index(1, 0)]
+fn test_decrease_execution_index(#[case] target_index: TxIndex, #[case] execution_index: TxIndex) {
     let scheduler =
         default_scheduler!(chunk_size: DEFAULT_CHUNK_SIZE, execution_index: execution_index);
     scheduler.decrease_execution_index(target_index);
     let expected_execution_index = min(target_index, execution_index);
     assert_eq!(scheduler.execution_index.load(Ordering::Acquire), expected_execution_index);
+    let expected_decrease_counter = if target_index < execution_index { 1 } else { 0 };
     assert_eq!(scheduler.decrease_counter.load(Ordering::Acquire), expected_decrease_counter);
 }
 
 #[rstest]
-#[case::from_ready_to_execute_to_executing(0, Some(0), 1)]
-#[case::index_out_of_bounds(DEFAULT_CHUNK_SIZE, None, 0)]
+#[case::ready_to_execute(0, TransactionStatus::ReadyToExecute, Some(0))]
+#[case::executing(0, TransactionStatus::Executing, None)]
+#[case::executed(0, TransactionStatus::Executed, None)]
+#[case::aborting(0, TransactionStatus::Aborting, None)]
+#[case::index_out_of_bounds(DEFAULT_CHUNK_SIZE, TransactionStatus::ReadyToExecute, None)]
 fn test_try_incarnate(
-    #[case] tx_index: usize,
-    #[case] expected_output: Option<usize>,
-    #[case] expected_n_active_tasks: usize,
+    #[case] tx_index: TxIndex,
+    #[case] tx_status: TransactionStatus,
+    #[case] expected_output: Option<TxIndex>,
 ) {
     let scheduler = default_scheduler!(chunk_size: DEFAULT_CHUNK_SIZE, n_active_tasks: 1);
+    scheduler.set_tx_status(tx_index, tx_status);
     assert_eq!(scheduler.try_incarnate(tx_index), expected_output);
-    assert_eq!(scheduler.n_active_tasks.load(Ordering::Acquire), expected_n_active_tasks);
+    if expected_output.is_some() {
+        assert_eq!(*scheduler.lock_tx_status(tx_index), TransactionStatus::Executing);
+        assert_eq!(scheduler.n_active_tasks.load(Ordering::Acquire), 1);
+    } else {
+        assert_eq!(scheduler.n_active_tasks.load(Ordering::Acquire), 0);
+        if tx_index < DEFAULT_CHUNK_SIZE {
+            assert_eq!(*scheduler.lock_tx_status(tx_index), tx_status);
+        }
+    }
 }
 
 #[rstest]
-#[case::some(1, Some(1), 2, 1)]
-#[case::none(DEFAULT_CHUNK_SIZE, None, DEFAULT_CHUNK_SIZE, 0)]
+#[case::ready_to_execute(1, TransactionStatus::ReadyToExecute, None)]
+#[case::executing(1, TransactionStatus::Executing, None)]
+#[case::executed(1, TransactionStatus::Executed, Some(1))]
+#[case::aborting(1, TransactionStatus::Aborting, None)]
+#[case::index_out_of_bounds(DEFAULT_CHUNK_SIZE, TransactionStatus::ReadyToExecute, None)]
 fn test_next_version_to_validate(
-    #[case] validation_index: usize,
-    #[case] expected_output: Option<usize>,
-    #[case] expected_validation_index: usize,
-    #[case] expected_n_active_tasks: usize,
+    #[case] validation_index: TxIndex,
+    #[case] tx_status: TransactionStatus,
+    #[case] expected_output: Option<TxIndex>,
 ) {
     let scheduler =
         default_scheduler!(chunk_size: DEFAULT_CHUNK_SIZE, validation_index: validation_index);
+    scheduler.set_tx_status(validation_index, tx_status);
     assert_eq!(scheduler.next_version_to_validate(), expected_output);
+    let expected_validation_index =
+        if validation_index < DEFAULT_CHUNK_SIZE { validation_index + 1 } else { validation_index };
     assert_eq!(scheduler.validation_index.load(Ordering::Acquire), expected_validation_index);
+    let expected_n_active_tasks = if expected_output.is_some() { 1 } else { 0 };
     assert_eq!(scheduler.n_active_tasks.load(Ordering::Acquire), expected_n_active_tasks);
 }
 
 #[rstest]
-#[case::some(1, Some(1), 2, 1)]
-#[case::none(DEFAULT_CHUNK_SIZE, None, DEFAULT_CHUNK_SIZE, 0)]
+#[case::ready_to_execute(1, TransactionStatus::ReadyToExecute, Some(1))]
+#[case::executing(1, TransactionStatus::Executing, None)]
+#[case::executed(1, TransactionStatus::Executed, None)]
+#[case::aborting(1, TransactionStatus::Aborting, None)]
+#[case::index_out_of_bounds(DEFAULT_CHUNK_SIZE, TransactionStatus::ReadyToExecute, None)]
 fn test_next_version_to_execute(
-    #[case] execution_index: usize,
-    #[case] expected_output: Option<usize>,
-    #[case] expected_execution_index: usize,
-    #[case] expected_n_active_tasks: usize,
+    #[case] execution_index: TxIndex,
+    #[case] tx_status: TransactionStatus,
+    #[case] expected_output: Option<TxIndex>,
 ) {
     let scheduler =
         default_scheduler!(chunk_size: DEFAULT_CHUNK_SIZE, execution_index: execution_index);
+    scheduler.set_tx_status(execution_index, tx_status);
     assert_eq!(scheduler.next_version_to_execute(), expected_output);
+    let expected_execution_index =
+        if execution_index < DEFAULT_CHUNK_SIZE { execution_index + 1 } else { execution_index };
     assert_eq!(scheduler.execution_index.load(Ordering::Acquire), expected_execution_index);
+    let expected_n_active_tasks = if expected_output.is_some() { 1 } else { 0 };
     assert_eq!(scheduler.n_active_tasks.load(Ordering::Acquire), expected_n_active_tasks);
 }