Kernel: Move block condition evaluation out of the Scheduler

This makes the Scheduler a lot leaner by not having to evaluate
block conditions every time it is invoked. Instead evaluate them as
the states change, and unblock threads at that point.

This also implements some more waitid/waitpid/wait features and
behavior. For example, WUNTRACED and WNOWAIT are now supported. And
wait will now not return EINTR when SIGCHLD is delivered at the
same time.

Kernel/TTY/MasterPTY.cpp

@@ -45,6 +45,11 @@ MasterPTY::MasterPTY(unsigned index)
     auto process = Process::current();
     set_uid(process->uid());
     set_gid(process->gid());
+
+    m_buffer.set_unblock_callback([this]() {
+        if (m_slave)
+            evaluate_block_conditions();
+    });
 }
 
 MasterPTY::~MasterPTY()

Kernel/TTY/SlavePTY.cpp

@@ -71,10 +71,11 @@ void SlavePTY::on_master_write(const UserOrKernelBuffer& buffer, ssize_t size)
 {
     ssize_t nread = buffer.read_buffered<128>(size, [&](const u8* data, size_t data_size) {
         for (size_t i = 0; i < data_size; ++i)
-            emit(data[i]);
+            emit(data[i], false);
         return (ssize_t)data_size;
     });
-    (void)nread;
+    if (nread > 0)
+        evaluate_block_conditions();
 }
 
 ssize_t SlavePTY::on_tty_write(const UserOrKernelBuffer& data, ssize_t size)
@@ -108,4 +109,9 @@ KResult SlavePTY::close()
     return KSuccess;
 }
 
+FileBlockCondition& SlavePTY::block_condition()
+{
+    return m_master->block_condition();
+}
+
 }

Kernel/TTY/SlavePTY.h

@@ -42,6 +42,8 @@ public:
 
     time_t time_of_last_write() const { return m_time_of_last_write; }
 
+    virtual FileBlockCondition& block_condition() override;
+
 private:
     // ^TTY
     virtual String tty_name() const override;

Kernel/TTY/TTY.cpp

@@ -24,6 +24,7 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <AK/ScopeGuard.h>
 #include <Kernel/Process.h>
 #include <Kernel/TTY/TTY.h>
 #include <LibC/errno_numbers.h>
@@ -64,6 +65,7 @@ KResultOr<size_t> TTY::read(FileDescription&, size_t, UserOrKernelBuffer& buffer
         size = m_input_buffer.size();
 
     ssize_t nwritten;
+    bool need_evaluate_block_conditions = false;
     if (in_canonical_mode()) {
         nwritten = buffer.write_buffered<512>(size, [&](u8* data, size_t data_size) {
             size_t i = 0;
@@ -73,6 +75,7 @@ KResultOr<size_t> TTY::read(FileDescription&, size_t, UserOrKernelBuffer& buffer
                     //Here we handle a ^D line, so we don't add the
                     //character to the output.
                     m_available_lines--;
+                    need_evaluate_block_conditions = true;
                     break;
                 } else if (ch == '\n' || is_eol(ch)) {
                     data[i] = ch;
@@ -93,6 +96,8 @@ KResultOr<size_t> TTY::read(FileDescription&, size_t, UserOrKernelBuffer& buffer
     }
     if (nwritten < 0)
         return KResult(nwritten);
+    if (nwritten > 0 || need_evaluate_block_conditions)
+        evaluate_block_conditions();
     return (size_t)nwritten;
 }
 
@@ -145,7 +150,7 @@ bool TTY::is_werase(u8 ch) const
     return ch == m_termios.c_cc[VWERASE];
 }
 
-void TTY::emit(u8 ch)
+void TTY::emit(u8 ch, bool do_evaluate_block_conditions)
 {
     if (should_generate_signals()) {
         if (ch == m_termios.c_cc[VINFO]) {
@@ -173,6 +178,11 @@ void TTY::emit(u8 ch)
         }
     }
 
+    ScopeGuard guard([&]() {
+        if (do_evaluate_block_conditions)
+            evaluate_block_conditions();
+    });
+
     if (in_canonical_mode()) {
         if (is_eof(ch)) {
             m_available_lines++;
@@ -218,6 +228,8 @@ void TTY::do_backspace()
         echo(8);
         echo(' ');
         echo(8);
+
+        evaluate_block_conditions();
     }
 }
 
@@ -231,6 +243,7 @@ void TTY::erase_word()
     //Note: if we have leading whitespace before the word
     //we want to delete we have to also delete that.
     bool first_char = false;
+    bool did_dequeue = false;
     while (can_do_backspace()) {
         u8 ch = m_input_buffer.last();
         if (ch == ' ' && first_char)
@@ -238,16 +251,23 @@ void TTY::erase_word()
         if (ch != ' ')
             first_char = true;
         m_input_buffer.dequeue_end();
+        did_dequeue = true;
         erase_character();
     }
+    if (did_dequeue)
+        evaluate_block_conditions();
 }
 
 void TTY::kill_line()
 {
+    bool did_dequeue = false;
     while (can_do_backspace()) {
         m_input_buffer.dequeue_end();
+        did_dequeue = true;
         erase_character();
     }
+    if (did_dequeue)
+        evaluate_block_conditions();
 }
 
 void TTY::erase_character()
@@ -277,6 +297,7 @@ void TTY::flush_input()
 {
     m_available_lines = 0;
     m_input_buffer.clear();
+    evaluate_block_conditions();
 }
 
 void TTY::set_termios(const termios& t)
@@ -330,7 +351,7 @@ int TTY::ioctl(FileDescription&, unsigned request, FlatPtr arg)
             return -EPERM;
         if (process && pgid != process->pgid())
             return -EPERM;
-        m_pg = *process_group;
+        m_pg = process_group;
 
         if (process) {
             if (auto parent = Process::from_pid(process->ppid())) {

Kernel/TTY/TTY.h

@@ -72,7 +72,7 @@ protected:
     void set_size(unsigned short columns, unsigned short rows);
 
     TTY(unsigned major, unsigned minor);
-    void emit(u8);
+    void emit(u8, bool do_evaluate_block_conditions = false);
     virtual void echo(u8) = 0;
 
     bool can_do_backspace() const;