Improve multithreading

test/libc/thread/pthread_cancel_masked_read_test.c

@@ -0,0 +1,41 @@
+#include <errno.h>
+#include <pthread.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+int pfds[2];
+int got_cleanup;
+
+void cleanup(void* arg) {
+  got_cleanup = 1;
+}
+
+void* worker(void* arg) {
+  char buf[8];
+  if (pthread_setcancelstate(PTHREAD_CANCEL_MASKED, 0))
+    _Exit(10);
+  pthread_cleanup_push(cleanup, 0);
+  if (read(pfds[0], buf, sizeof(buf)) != -1)
+    _Exit(11);
+  if (errno != ECANCELED)
+    _Exit(12);
+  pthread_cleanup_pop(0);
+  return (void*)123;
+}
+
+int main(int argc, char* argv[]) {
+  void* rc;
+  pthread_t th;
+  if (pipe(pfds))
+    return 1;
+  if (pthread_create(&th, 0, worker, 0))
+    return 2;
+  if (pthread_cancel(th))
+    return 3;
+  if (pthread_join(th, &rc))
+    return 4;
+  if (rc != (void*)123)
+    return 5;
+  if (got_cleanup)
+    return 7;
+}