From aca21731ff7636d67c524101ae87398079868eb8 Mon Sep 17 00:00:00 2001
From: Augustin Cavalier <waddlesplash@gmail.com>
Date: Tue, 25 Jul 2023 15:27:40 -0400
Subject: [PATCH] kernel/condition_variable: Return the count of unblocked
 threads from Notify.

No reason not to, and it's needed in user_mutex to avoid a very rare
potential race, anyway.
---
 headers/private/kernel/condition_variable.h | 22 ++++++++---------
 src/system/kernel/condition_variable.cpp    | 27 ++++++++++++---------
 2 files changed, 27 insertions(+), 22 deletions(-)

diff --git a/headers/private/kernel/condition_variable.h b/headers/private/kernel/condition_variable.h
index 43ef0186c9..e57dd67df5 100644
--- a/headers/private/kernel/condition_variable.h
+++ b/headers/private/kernel/condition_variable.h
@@ -58,11 +58,11 @@ public:
 									const char* objectType);
 			void				Unpublish();
 
-	inline	void				NotifyOne(status_t result = B_OK);
-	inline	void				NotifyAll(status_t result = B_OK);
+	inline	int32				NotifyOne(status_t result = B_OK);
+	inline	int32				NotifyAll(status_t result = B_OK);
 
-	static	void				NotifyOne(const void* object, status_t result);
-	static	void				NotifyAll(const void* object, status_t result);
+	static	int32				NotifyOne(const void* object, status_t result);
+	static	int32				NotifyAll(const void* object, status_t result);
 
 			void				Add(ConditionVariableEntry* entry);
 			int32				EntriesCount()		{ return atomic_get(&fEntriesCount); }
@@ -79,9 +79,9 @@ public:
 			void				Dump() const;
 
 private:
-	static 	void				_Notify(const void* object, bool all, status_t result);
-			void				_Notify(bool all, status_t result);
-			void				_NotifyLocked(bool all, status_t result);
+	static 	int32				_Notify(const void* object, bool all, status_t result);
+			int32				_Notify(bool all, status_t result);
+			int32				_NotifyLocked(bool all, status_t result);
 
 protected:
 			typedef DoublyLinkedList<ConditionVariableEntry> EntryList;
@@ -102,17 +102,17 @@ protected:
 };
 
 
-inline void
+inline int32
 ConditionVariable::NotifyOne(status_t result)
 {
-	_Notify(false, result);
+	return _Notify(false, result);
 }
 
 
-inline void
+inline int32
 ConditionVariable::NotifyAll(status_t result)
 {
-	_Notify(true, result);
+	return _Notify(true, result);
 }
 
 
diff --git a/src/system/kernel/condition_variable.cpp b/src/system/kernel/condition_variable.cpp
index 1691645a6a..7f9785f877 100644
--- a/src/system/kernel/condition_variable.cpp
+++ b/src/system/kernel/condition_variable.cpp
@@ -324,56 +324,58 @@ ConditionVariable::Wait(recursive_lock* lock, uint32 flags, bigtime_t timeout)
 }
 
 
-/*static*/ void
+/*static*/ int32
 ConditionVariable::NotifyOne(const void* object, status_t result)
 {
-	_Notify(object, false, result);
+	return _Notify(object, false, result);
 }
 
 
-/*static*/ void
+/*static*/ int32
 ConditionVariable::NotifyAll(const void* object, status_t result)
 {
-	_Notify(object, true, result);
+	return _Notify(object, true, result);
 }
 
 
-/*static*/ void
+/*static*/ int32
 ConditionVariable::_Notify(const void* object, bool all, status_t result)
 {
 	InterruptsLocker ints;
 	ReadSpinLocker hashLocker(sConditionVariableHashLock);
 	ConditionVariable* variable = sConditionVariableHash.Lookup(object);
 	if (variable == NULL)
-		return;
+		return 0;
 	SpinLocker variableLocker(variable->fLock);
 	hashLocker.Unlock();
 
-	variable->_NotifyLocked(all, result);
+	return variable->_NotifyLocked(all, result);
 }
 
 
-void
+int32
 ConditionVariable::_Notify(bool all, status_t result)
 {
 	InterruptsSpinLocker _(fLock);
-
 	if (!fEntries.IsEmpty()) {
 		if (result > B_OK) {
 			panic("tried to notify with invalid result %" B_PRId32 "\n", result);
 			result = B_ERROR;
 		}
 
-		_NotifyLocked(all, result);
+		return _NotifyLocked(all, result);
 	}
+	return 0;
 }
 
 
 /*! Called with interrupts disabled and the condition variable's spinlock held.
  */
-void
+int32
 ConditionVariable::_NotifyLocked(bool all, status_t result)
 {
+	int32 notified = 0;
+
 	// Dequeue and wake up the blocked threads.
 	while (ConditionVariableEntry* entry = fEntries.RemoveHead()) {
 		Thread* thread = atomic_pointer_get_and_set(&entry->fThread, (Thread*)NULL);
@@ -417,9 +419,12 @@ ConditionVariable::_NotifyLocked(bool all, status_t result)
 				thread_unblock_locked(thread, result);
 		}
 
+		notified++;
 		if (!all)
 			break;
 	}
+
+	return notified;
 }