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.

1 files changed, 7 insertions, 32 deletions

diff --git a/Userland/strace.cpp b/Userland/strace.cpp
index 6922218bb7..00bd6fbeec 100644
--- a/Userland/strace.cpp
+++ b/Userland/strace.cpp
@@ -53,7 +53,6 @@ static void handle_sigint(int)
 int main(int argc, char** argv)
 {
     Vector<const char*> child_argv;
-    bool spawned_new_process = false;
 
     Core::ArgsParser parser;
     parser.add_option(g_pid, "Trace the given PID", "pid", 'p', "pid");
@@ -61,6 +60,7 @@ int main(int argc, char** argv)
 
     parser.parse(argc, argv);
 
+    int status;
     if (g_pid == -1) {
         if (child_argv.is_empty()) {
             fprintf(stderr, "strace: Expected either a pid or some arguments\n");
@@ -68,7 +68,6 @@ int main(int argc, char** argv)
         }
 
         child_argv.append(nullptr);
-        spawned_new_process = true;
         int pid = fork();
         if (pid < 0) {
             perror("fork");
@@ -89,7 +88,7 @@ int main(int argc, char** argv)
         }
 
         g_pid = pid;
-        if (waitpid(pid, nullptr, WSTOPPED) != pid) {
+        if (waitpid(pid, &status, WSTOPPED | WEXITED) != pid || !WIFSTOPPED(status)) {
             perror("waitpid");
             return 1;
         }
@@ -104,66 +103,42 @@ int main(int argc, char** argv)
         perror("attach");
         return 1;
     }
-
-    if (waitpid(g_pid, nullptr, WSTOPPED) != g_pid) {
+    if (waitpid(g_pid, &status, WSTOPPED | WEXITED) != g_pid || !WIFSTOPPED(status)) {
         perror("waitpid");
         return 1;
     }
 
-    if (spawned_new_process) {
-
-        if (ptrace(PT_CONTINUE, g_pid, 0, 0) < 0) {
-            perror("continue");
-            return 1;
-        }
-        if (waitpid(g_pid, nullptr, WSTOPPED) != g_pid) {
-            perror("wait_pid");
-            return 1;
-        }
-    }
-
     for (;;) {
         if (ptrace(PT_SYSCALL, g_pid, 0, 0) == -1) {
-            if (errno == ESRCH)
-                return 0;
             perror("syscall");
             return 1;
         }
-        if (waitpid(g_pid, nullptr, WSTOPPED) != g_pid) {
+        if (waitpid(g_pid, &status, WSTOPPED | WEXITED) != g_pid || !WIFSTOPPED(status)) {
             perror("wait_pid");
             return 1;
         }
-
         PtraceRegisters regs = {};
         if (ptrace(PT_GETREGS, g_pid, &regs, 0) == -1) {
             perror("getregs");
             return 1;
         }
-
         u32 syscall_index = regs.eax;
         u32 arg1 = regs.edx;
         u32 arg2 = regs.ecx;
         u32 arg3 = regs.ebx;
 
-        // skip syscall exit
         if (ptrace(PT_SYSCALL, g_pid, 0, 0) == -1) {
-            if (errno == ESRCH)
-                return 0;
             perror("syscall");
             return 1;
         }
-        if (waitpid(g_pid, nullptr, WSTOPPED) != g_pid) {
+        if (waitpid(g_pid, &status, WSTOPPED | WEXITED) != g_pid || !WIFSTOPPED(status)) {
             perror("wait_pid");
             return 1;
         }
 
         if (ptrace(PT_GETREGS, g_pid, &regs, 0) == -1) {
-            if (errno == ESRCH && syscall_index == SC_exit) {
-                regs.eax = 0;
-            } else {
-                perror("getregs");
-                return 1;
-            }
+            perror("getregs");
+            return 1;
         }
 
         u32 res = regs.eax;