Improve synchronization

- Fix bugs in kDos2Errno definition
- malloc() should now be thread safe
- Fix bug in rollup.com header generator
- Fix open(O_APPEND) on the New Technology
- Fix select() on the New Technology and test it
- Work towards refactoring i/o for thread safety
- Socket reads and writes on NT now poll for signals
- Work towards i/o completion ports on the New Technology
- Make read() and write() intermittently check for signals
- Blinkenlights keyboard i/o so much better on NT w/ poll()
- You can now poll() files and sockets at the same time on NT
- Fix bug in appendr() that manifests with dlmalloc footers off

libc/calls/reservefd.c

@@ -16,24 +16,98 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/assert.h"
+#include "libc/bits/weaken.h"
+#include "libc/calls/calls.h"
 #include "libc/calls/internal.h"
-#include "libc/intrin/cmpxchg.h"
+#include "libc/calls/strace.internal.h"
+#include "libc/intrin/kprintf.h"
+#include "libc/intrin/spinlock.h"
+#include "libc/macros.internal.h"
 #include "libc/mem/mem.h"
+#include "libc/runtime/runtime.h"
+#include "libc/str/str.h"
 #include "libc/sysv/errfuns.h"
 
+/**
+ * Grows file descriptor array memory if needed.
+ */
+int __ensurefds(int fd) {
+  size_t n1, n2;
+  struct Fd *p1, *p2;
+  _spinlock(&__fds_lock);
+  n1 = g_fds.n;
+  if (fd >= n1) {
+    STRACE("__ensurefds(%d) extending", fd);
+    if (weaken(malloc)) {
+      // TODO(jart): we need a semaphore for this
+      p1 = g_fds.p;
+      n2 = fd + (fd >> 1);
+      if ((p2 = weaken(malloc)(n2 * sizeof(*p1)))) {
+        memcpy(p2, p1, n1 * sizeof(*p1));
+        g_fds.p = p2;
+        g_fds.n = n2;
+        if (p1 != g_fds.__init_p) {
+          weaken(free)(p1);
+        }
+      } else {
+        fd = enomem();
+      }
+    } else {
+      fd = emfile();
+    }
+  }
+  _spunlock(&__fds_lock);
+  return fd;
+}
+
 /**
  * Finds open file descriptor slot.
  */
-int __reservefd(void) {
+int __reservefd(int start) {
   int fd;
   for (;;) {
-    fd = g_fds.f;
-    if (fd >= g_fds.n) {
-      if (__ensurefds(fd) == -1) return -1;
-    }
-    _cmpxchg(&g_fds.f, fd, fd + 1);
-    if (_cmpxchg(&g_fds.p[fd].kind, kFdEmpty, kFdReserved)) {
+    _spinlock(&__fds_lock);
+    fd = start < 0 ? g_fds.f : start;
+    while (fd < g_fds.n && g_fds.p[fd].kind) ++fd;
+    if (fd < g_fds.n) {
+      g_fds.f = fd + 1;
+      bzero(g_fds.p + fd, sizeof(*g_fds.p));
+      g_fds.p[fd].kind = kFdReserved;
+      _spunlock(&__fds_lock);
       return fd;
+    } else {
+      _spunlock(&__fds_lock);
+      if (__ensurefds(fd) == -1) {
+        return -1;
+      }
     }
   }
 }
+
+/**
+ * Closes non-stdio file descriptors to free dynamic memory.
+ */
+static void __freefds(void) {
+  int i;
+  STRACE("__freefds()");
+  for (i = 3; i < g_fds.n; ++i) {
+    if (g_fds.p[i].kind) {
+      close(i);
+    }
+  }
+  if (g_fds.p != g_fds.__init_p) {
+    memcpy(g_fds.__init_p, g_fds.p, sizeof(*g_fds.p) * 3);
+    weaken(free)(g_fds.p);
+    g_fds.p = g_fds.__init_p;
+    g_fds.n = ARRAYLEN(g_fds.__init_p);
+  }
+}
+
+static textstartup void __freefds_init(void) {
+  atexit(__freefds);
+}
+
+const void *const __freefds_ctor[] initarray = {
+    __freefds_init,
+};