Kernel/LibC: Implement pthread_join

kernel/include/kernel/Process.h

@@ -185,6 +185,7 @@ namespace Kernel
 		BAN::ErrorOr<long> sys_yield();
 		BAN::ErrorOr<long> sys_pthread_create(const pthread_attr_t* __restrict attr, void (*entry)(void*), void* arg);
 		BAN::ErrorOr<long> sys_pthread_exit(void* value);
+		BAN::ErrorOr<long> sys_pthread_join(pthread_t thread, void** value);
 		BAN::ErrorOr<long> sys_pthread_self();
 
 		BAN::ErrorOr<long> sys_tcgetpgrp(int fd);
@@ -297,10 +298,11 @@ namespace Kernel
 
 		struct pthread_info_t
 		{
-			Thread* thread;
+			pthread_t thread;
 			void* value;
 		};
 		BAN::Vector<pthread_info_t> m_exited_pthreads;
+		ThreadBlocker m_pthread_exit_blocker;
 
 		uint64_t m_alarm_interval_ns { 0 };
 		uint64_t m_alarm_wake_time_ns { 0 };

kernel/kernel/Process.cpp

@@ -2115,11 +2115,12 @@ namespace Kernel
 		if (&Thread::current() == m_threads.front())
 			return BAN::Error::from_errno(EINVAL);
 
-		TRY(m_exited_pthreads.emplace_back(&Thread::current(), value));
+		TRY(m_exited_pthreads.emplace_back(Thread::current().tid(), value));
 		for (auto* thread : m_threads)
 		{
 			if (thread != &Thread::current())
 				continue;
+			m_pthread_exit_blocker.unblock();
 			m_process_lock.unlock();
 			thread->on_exit();
 		}
@@ -2127,6 +2128,58 @@ namespace Kernel
 		ASSERT_NOT_REACHED();
 	}
 
+	BAN::ErrorOr<long> Process::sys_pthread_join(pthread_t thread, void** value)
+	{
+		LockGuard _(m_process_lock);
+
+		if (value)
+			TRY(validate_pointer_access(value, sizeof(void*), true));
+
+		if (thread == Thread::current().tid())
+			return BAN::Error::from_errno(EINVAL);
+
+		const auto wait_thread =
+			[&]() -> bool
+			{
+				for (size_t i = 0; i < m_exited_pthreads.size(); i++)
+				{
+					if (m_exited_pthreads[i].thread != thread)
+						continue;
+
+					if (value)
+						*value = m_exited_pthreads[i].value;
+					m_exited_pthreads.remove(i);
+
+					return true;
+				}
+
+				return false;
+			};
+
+		if (wait_thread())
+			return 0;
+
+		{
+			bool found = false;
+			for (auto* _thread : m_threads)
+				if (_thread->tid() == thread)
+					found = true;
+			if (!found)
+				return BAN::Error::from_errno(EINVAL);
+		}
+
+		for (;;)
+		{
+			{
+				LockFreeGuard _(m_process_lock);
+				m_pthread_exit_blocker.block_with_timeout_ms(100);
+			}
+
+			if (wait_thread())
+				return 0;
+		}
+	}
+
 	BAN::ErrorOr<long> Process::sys_pthread_self()
 	{
 		return Thread::current().tid();

userspace/libraries/LibC/include/sys/syscall.h

@@ -93,6 +93,7 @@ __BEGIN_DECLS
 	O(SYS_YIELD,			yield)			\
 	O(SYS_PTHREAD_CREATE,	pthread_create)	\
 	O(SYS_PTHREAD_EXIT,		pthread_exit)	\
+	O(SYS_PTHREAD_JOIN,		pthread_join)	\
 	O(SYS_PTHREAD_SELF,		pthread_self)	\
 
 enum Syscall

userspace/libraries/LibC/pthread.cpp

@@ -55,6 +55,11 @@ void pthread_exit(void* value_ptr)
 	ASSERT_NOT_REACHED();
 }
 
+int pthread_join(pthread_t thread, void** value_ptr)
+{
+	return syscall(SYS_PTHREAD_JOIN, thread, value_ptr);
+}
+
 pthread_t pthread_self(void)
 {
 	return syscall(SYS_PTHREAD_SELF);