Enforce absolute Wasm invocation deadlines

src/lib/sys.cpp

@@ -1396,6 +1396,48 @@ std::map<pid_t, Worker> workers;
 #include <sys/resource.h>
 #include <sys/prctl.h>
 
+// The process-wide reaper may run on a runtime thread while a request thread
+// synchronously owns a child. Preserve unknown statuses until that owner takes
+// them instead of forcing it to guess success after waitpid reports ECHILD.
+static const size_t child_exit_status_capacity = 256;
+static volatile sig_atomic_t child_exit_status_cursor = 0;
+static volatile sig_atomic_t child_exit_status_pids[child_exit_status_capacity] = {0};
+static volatile sig_atomic_t child_exit_status_values[child_exit_status_capacity] = {0};
+static volatile sig_atomic_t child_exit_status_sequences[child_exit_status_capacity] = {0};
+
+static void child_exit_status_publish(pid_t pid, int status)
+{
+	sig_atomic_t cursor = __atomic_fetch_add(&child_exit_status_cursor, 1, __ATOMIC_RELAXED);
+	size_t slot = (size_t)(unsigned int)cursor % child_exit_status_capacity;
+	__atomic_store_n(&child_exit_status_pids[slot], 0, __ATOMIC_RELEASE);
+	__atomic_store_n(&child_exit_status_values[slot], (sig_atomic_t)status, __ATOMIC_RELAXED);
+	__atomic_store_n(&child_exit_status_sequences[slot], cursor + 1, __ATOMIC_RELAXED);
+	__atomic_store_n(&child_exit_status_pids[slot], (sig_atomic_t)pid, __ATOMIC_RELEASE);
+}
+
+unsigned int child_exit_status_snapshot()
+{
+	return((unsigned int)__atomic_load_n(&child_exit_status_cursor, __ATOMIC_ACQUIRE));
+}
+
+bool child_exit_status_take(pid_t pid, int& status, unsigned int since)
+{
+	for(size_t slot = 0; slot < child_exit_status_capacity; slot++)
+	{
+		unsigned int sequence = (unsigned int)__atomic_load_n(&child_exit_status_sequences[slot], __ATOMIC_ACQUIRE);
+		unsigned int distance = sequence - since;
+		if(sequence == 0 || distance == 0 || distance >= 0x80000000u)
+			continue;
+		sig_atomic_t expected = (sig_atomic_t)pid;
+		if(__atomic_compare_exchange_n(&child_exit_status_pids[slot], &expected, 0, false, __ATOMIC_ACQUIRE, __ATOMIC_RELAXED))
+		{
+			status = (int)__atomic_load_n(&child_exit_status_values[slot], __ATOMIC_RELAXED);
+			return(true);
+		}
+	}
+	return(false);
+}
+
 pid_t spawn_subprocess(std::function<void()> exec_after_spawn)
 {
 	parent_pid = getpid();
@@ -1648,6 +1690,7 @@ void on_child_exit(int sig)
 		}
 		else
 		{
+			child_exit_status_publish(pid, status);
 			printf("(P) task child reaped (PID:%i)\n", pid);
 		}
 	}

src/lib/sys.h

@@ -21,6 +21,8 @@ s32 usleep(u32 usec);
 #else
 #include <sys/file.h>
 #include <signal.h>
+unsigned int child_exit_status_snapshot();
+bool child_exit_status_take(pid_t pid, int& status, unsigned int since);
 #endif
 #include <ctime>
 #include <sstream>