Make some fixups to POSIX threads

libc/integral/c.inc

@@ -593,7 +593,7 @@ typedef struct {
 
 #define notpossible \
   do {              \
-    asm("hlt");     \
+    asm("ud2");     \
     unreachable;    \
   } while (0)
 

libc/intrin/exit1.greg.c

@@ -18,38 +18,56 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/strace.internal.h"
 #include "libc/dce.h"
+#include "libc/intrin/asmflag.h"
 #include "libc/intrin/promises.internal.h"
 #include "libc/nt/thread.h"
 #include "libc/runtime/runtime.h"
 #include "libc/sysv/consts/nr.h"
 
+__msabi extern typeof(ExitThread) *const __imp_ExitThread;
+
 /**
  * Terminates thread with raw system call.
  *
+ * If this is the main thread, or an orphaned child thread, then this
+ * function is equivalent to exiting the process; however, `rc` shall
+ * only be reported to the parent process on Linux, FreeBSD & Windows
+ * whereas on other platforms, it'll be silently coerced to zero.
+ *
  * @param rc only works on Linux and Windows
  * @see cthread_exit()
  * @threadsafe
  * @noreturn
  */
 privileged wontreturn void _Exit1(int rc) {
-  struct WinThread *wt;
+  char cf;
+  int ax, dx, di, si;
   STRACE("_Exit1(%d)", rc);
   if (!IsWindows() && !IsMetal()) {
-    if (IsOpenbsd() && !PLEDGED(STDIO)) {
+    // exit() on Linux
+    // thr_exit() on FreeBSD
+    // __threxit() on OpenBSD
+    // __lwp_exit() on NetBSD
+    // __bsdthread_terminate() on XNU
+    asm volatile(CFLAG_ASM("xor\t%%r10d,%%r10d\n\t"
+                           "syscall")
+                 : CFLAG_CONSTRAINT(cf), "=a"(ax), "=d"(dx), "=D"(di), "=S"(si)
+                 : "1"(__NR_exit), "3"(IsLinux() ? rc : 0), "4"(0), "2"(0)
+                 : "rcx", "r8", "r9", "r10", "r11", "memory");
+    if ((IsFreebsd() && !cf && !ax) || (SupportsFreebsd() && IsTiny())) {
+      // FreeBSD checks if this is either the main thread by itself, or
+      // the last running child thread in which case thr_exit() returns
+      // zero with an error. In that case we'll exit the whole process.
+      // FreeBSD thr_exit() can even clobber registers, like r8 and r9!
       asm volatile("syscall"
                    : /* no outputs */
-                   : "a"(__NR_exit), "D"(rc)
+                   : "a"(__NR_exit_group), "D"(rc)
                    : "rcx", "r11", "memory");
+      unreachable;
     }
-    asm volatile("xor\t%%r10d,%%r10d\n\t"
-                 "syscall"
-                 : /* no outputs */
-                 : "a"(__NR_exit), "D"(IsLinux() ? rc : 0), "S"(0), "d"(0)
-                 : "rcx", "r10", "r11", "memory");
   } else if (IsWindows()) {
-    ExitThread(rc);
-  }
-  for (;;) {
-    asm("ud2");
+    __imp_ExitThread(rc);
+    unreachable;
   }
+  notpossible;
 }

libc/intrin/pthread_mutex_lock.c

@@ -100,7 +100,7 @@ static int pthread_mutex_lock_spin(pthread_mutex_t *mutex, int expect,
  *     PTHREAD_MUTEX_ERRORCHECK    :   917c (296ns)
  *
  * @return 0 on success, or error number on failure
- * @see pthread_spin_lock
+ * @see pthread_spin_lock()
  */
 int pthread_mutex_lock(pthread_mutex_t *mutex) {
   int c, me, owner, tries;

libc/thread/posixthread.internal.h

@@ -10,10 +10,46 @@ COSMOPOLITAN_C_START_
  * @fileoverview Cosmopolitan POSIX Thread Internals
  */
 
+// LEGAL TRANSITIONS             ┌──> TERMINATED
+// pthread_create ─┬─> JOINABLE ─┴┬─> DETACHED ──> ZOMBIE
+//                 └──────────────┘
 enum PosixThreadStatus {
+
+  // this is a running thread that needs pthread_join()
+  //
+  // the following transitions are possible:
+  //
+  // - kPosixThreadJoinable -> kPosixThreadTerminated if start_routine()
+  //   returns, or is longjmp'd out of by pthread_exit(), and the thread
+  //   is waiting to be joined.
+  //
+  // - kPosixThreadJoinable -> kPosixThreadDetached if pthread_detach()
+  //   is called on this thread.
   kPosixThreadJoinable,
+
+  // this is a managed thread that'll be cleaned up by the library.
+  //
+  // the following transitions are possible:
+  //
+  // - kPosixThreadDetached -> kPosixThreadZombie if start_routine()
+  //   returns, or is longjmp'd out of by pthread_exit(), and the thread
+  //   is waiting to be joined.
   kPosixThreadDetached,
+
+  // this is a joinable thread that terminated.
+  //
+  // the following transitions are possible:
+  //
+  // - kPosixThreadTerminated -> _pthread_free() will happen when
+  //   pthread_join() is called by the user.
   kPosixThreadTerminated,
+
+  // this is a detached thread that terminated.
+  //
+  // the following transitions are possible:
+  //
+  // - kPosixThreadZombie -> _pthread_free() will happen whenever
+  //   convenient, e.g. pthread_create() entry or atexit handler.
   kPosixThreadZombie,
 };
 
@@ -28,11 +64,11 @@ struct PosixThread {
   pthread_attr_t attr;
 };
 
-void pthread_free(struct PosixThread *) hidden;
-void pthread_wait(struct PosixThread *) hidden;
-void pthread_zombies_add(struct PosixThread *) hidden;
-void pthread_zombies_decimate(void) hidden;
-void pthread_zombies_harvest(void) hidden;
+void _pthread_free(struct PosixThread *) hidden;
+void _pthread_wait(struct PosixThread *) hidden;
+void _pthread_zombies_add(struct PosixThread *) hidden;
+void _pthread_zombies_decimate(void) hidden;
+void _pthread_zombies_harvest(void) hidden;
 
 COSMOPOLITAN_C_END_
 #endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */

libc/thread/pthread_create.c

@@ -22,21 +22,23 @@
 #include "libc/intrin/atomic.h"
 #include "libc/intrin/pthread.h"
 #include "libc/intrin/wait0.internal.h"
+#include "libc/intrin/weaken.h"
 #include "libc/mem/mem.h"
 #include "libc/nexgen32e/gettls.h"
 #include "libc/runtime/runtime.h"
 #include "libc/sysv/consts/clone.h"
 #include "libc/sysv/consts/map.h"
 #include "libc/sysv/consts/prot.h"
+#include "libc/thread/internal.h"
 #include "libc/thread/posixthread.internal.h"
 #include "libc/thread/spawn.h"
 #include "libc/thread/thread.h"
 
-void pthread_wait(struct PosixThread *pt) {
+void _pthread_wait(struct PosixThread *pt) {
   _wait0(pt->spawn.ctid);
 }
 
-void pthread_free(struct PosixThread *pt) {
+void _pthread_free(struct PosixThread *pt) {
   free(pt->spawn.tls);
   if (pt->stacksize) {
     munmap(&pt->spawn.stk, pt->stacksize);
@@ -51,6 +53,9 @@ static int PosixThread(void *arg, int tid) {
     ((cthread_t)__get_tls())->pthread = pt;
     pt->rc = pt->start_routine(pt->arg);
   }
+  if (weaken(_pthread_key_destruct)) {
+    weaken(_pthread_key_destruct)(0);
+  }
   if (atomic_load_explicit(&pt->status, memory_order_acquire) ==
       kPosixThreadDetached) {
     atomic_store_explicit(&pt->status, kPosixThreadZombie,
@@ -71,18 +76,18 @@ static int PosixThread(void *arg, int tid) {
  *              │ pthread_create() │       - Standard
  *              └─────────┬────────┘         Abstraction
  *              ┌─────────┴────────┐
- *              │     _spawn()     │       - Cosmopolitan
- *              └─────────┬────────┘         Abstraction
- *              ┌─────────┴────────┐
  *              │     clone()      │       - Polyfill
  *              └─────────┬────────┘
- *            ┌────────┬──┴──┬─┬─────────┐ - Kernel
- *      ┌─────┴─────┐  │     │┌┴──────┐  │   Interfaces
- *      │ sys_clone │  │     ││ tfork │  │
- *      └───────────┘  │     │└───────┘ ┌┴─────────────┐
- *     ┌───────────────┴──┐ ┌┴────────┐ │ CreateThread │
- *     │ bsdthread_create │ │ thr_new │ └──────────────┘
- *     └──────────────────┘ └─────────┘
+ *            ┌────────┬──┴┬─┬─┬─────────┐ - Kernel
+ *      ┌─────┴─────┐  │   │ │┌┴──────┐  │   Interfaces
+ *      │ sys_clone │  │   │ ││ tfork │ ┌┴─────────────┐
+ *      └───────────┘  │   │ │└───────┘ │ CreateThread │
+ *     ┌───────────────┴──┐│┌┴────────┐ └──────────────┘
+ *     │ bsdthread_create │││ thr_new │
+ *     └──────────────────┘│└─────────┘
+ *                 ┌───────┴──────┐
+ *                 │ _lwp_create  │
+ *                 └──────────────┘
  *
  * @param thread if non-null is used to output the thread id
  *     upon successful completion
@@ -96,13 +101,14 @@ static int PosixThread(void *arg, int tid) {
  * @raise EINVAL if `attr` was supplied and had unnaceptable data
  * @raise EPERM if scheduling policy was requested and user account
  *     isn't authorized to use it
+ * @threadsafe
  */
 int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
                    void *(*start_routine)(void *), void *arg) {
   int rc, e = errno;
   struct PosixThread *pt;
   pthread_attr_t default_attr;
-  pthread_zombies_decimate();
+  _pthread_zombies_decimate();
 
   // default attributes
   if (!attr) {
@@ -140,7 +146,7 @@ int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
       pt->stacksize = attr->stacksize;
     } else {
       rc = errno;
-      pthread_free(pt);
+      _pthread_free(pt);
       errno = e;
       if (rc == EINVAL || rc == EOVERFLOW) {
         return EINVAL;
@@ -170,7 +176,7 @@ int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
     }
   }
 
-  // save the attributes for descriptive purposes
+  // we only need to save this to support pthread_getattr_np()
   pt->attr = *attr;
 
   // set initial status
@@ -180,10 +186,10 @@ int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
       break;
     case PTHREAD_CREATE_DETACHED:
       pt->status = kPosixThreadDetached;
-      pthread_zombies_add(pt);
+      _pthread_zombies_add(pt);
       break;
     default:
-      pthread_free(pt);
+      _pthread_free(pt);
       return EINVAL;
   }
 
@@ -195,7 +201,7 @@ int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
                 CLONE_CHILD_CLEARTID,
             pt, &pt->spawn.ptid, pt->spawn.tib, pt->spawn.ctid) == -1) {
     rc = errno;
-    pthread_free(pt);
+    _pthread_free(pt);
     errno = e;
     if (rc == EINVAL) {
       return EINVAL;

libc/thread/pthread_detach.c

@@ -34,17 +34,24 @@ int pthread_detach(pthread_t thread) {
   for (;;) {
     status = atomic_load_explicit(&pt->status, memory_order_relaxed);
     if (status == kPosixThreadDetached || status == kPosixThreadZombie) {
+      // these two states indicate the thread was already detached, in
+      // which case it's already listed under _pthread_zombies.
       break;
     } else if (status == kPosixThreadTerminated) {
-      pthread_wait(pt);
-      pthread_free(pt);
-      break;
-    } else if (status == kPosixThreadJoinable &&
-               atomic_compare_exchange_weak_explicit(
-                   &pt->status, &status, kPosixThreadDetached,
-                   memory_order_acquire, memory_order_relaxed)) {
-      pthread_zombies_add(pt);
+      // thread was joinable and finished running. since pthread_join
+      // won't be called, it's safe to free the thread resources now.
+      _pthread_wait(pt);
+      _pthread_free(pt);
       break;
+    } else if (status == kPosixThreadJoinable) {
+      if (atomic_compare_exchange_weak_explicit(
+              &pt->status, &status, kPosixThreadDetached, memory_order_acquire,
+              memory_order_relaxed)) {
+        _pthread_zombies_add(pt);
+        break;
+      }
+    } else {
+      notpossible;
     }
   }
   return 0;

libc/thread/pthread_exit.c

@@ -24,10 +24,22 @@
 
 /**
  * Terminates current POSIX thread.
+ *
+ * If this function is called from the main thread, or a thread created
+ * with clone() or _spawn(), then this function is the same as _Exit1()
+ * in which case `rc` is coerced to a `uint8_t` exit status, which will
+ * only be reported to the parent process on Linux, FreeBSD and Windows
+ *
+ * @param rc is reported later to pthread_join()
+ * @threadsafe
+ * @noreturn
  */
-void pthread_exit(void *rc) {
+wontreturn void pthread_exit(void *rc) {
   struct PosixThread *pt;
-  pt = ((cthread_t)__get_tls())->pthread;
-  pt->rc = rc;
-  longjmp(pt->exiter, 1);
+  if ((pt = ((cthread_t)__get_tls())->pthread)) {
+    pt->rc = rc;
+    longjmp(pt->exiter, 1);
+  } else {
+    _Exit1((int)(intptr_t)rc);
+  }
 }

libc/thread/pthread_join.c

@@ -32,14 +32,15 @@
  */
 int pthread_join(pthread_t thread, void **value_ptr) {
   struct PosixThread *pt = thread;
-  if (pt->status == kPosixThreadDetached) {
+  if (pt->status == kPosixThreadDetached ||  //
+      pt->status == kPosixThreadZombie) {
     assert(!"badjoin");
     return EDEADLK;
   }
-  pthread_wait(pt);
+  _pthread_wait(pt);
   if (value_ptr) {
     *value_ptr = pt->rc;
   }
-  pthread_free(pt);
+  _pthread_free(pt);
   return 0;
 }

libc/thread/pthread_key_create.c

@@ -41,7 +41,7 @@ int pthread_key_create(pthread_key_t *key, pthread_key_dtor dtor) {
 }
 
 static textexit void _pthread_key_atexit(void) {
-  _pthread_key_destruct(_pthread_keys);
+  _pthread_key_destruct(0);
 }
 
 __attribute__((__constructor__)) static textstartup void _pthread_key_init() {

libc/thread/pthread_key_destruct.c

@@ -25,6 +25,7 @@ void _pthread_key_destruct(void *key[PTHREAD_KEYS_MAX]) {
   uint64_t x;
   void *value;
   pthread_key_dtor dtor;
+  if (!key) key = _pthread_keys;
 StartOver:
   for (i = 0; i < (PTHREAD_KEYS_MAX + 63) / 64; ++i) {
     x = _pthread_key_usage[i];

libc/thread/zombie.c

@@ -17,6 +17,7 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/intrin/atomic.h"
+#include "libc/intrin/pthread.h"
 #include "libc/mem/mem.h"
 #include "libc/runtime/runtime.h"
 #include "libc/thread/posixthread.internal.h"
@@ -29,46 +30,46 @@
 static struct Zombie {
   struct Zombie *next;
   struct PosixThread *pt;
-} * pthread_zombies;
+} * _pthread_zombies;
 
-void pthread_zombies_add(struct PosixThread *pt) {
+void _pthread_zombies_add(struct PosixThread *pt) {
   struct Zombie *z;
   if ((z = malloc(sizeof(struct Zombie)))) {
     z->pt = pt;
-    z->next = atomic_load(&pthread_zombies);
+    z->next = atomic_load(&_pthread_zombies);
     for (;;) {
-      if (atomic_compare_exchange_weak(&pthread_zombies, &z->next, z)) {
+      if (atomic_compare_exchange_weak(&_pthread_zombies, &z->next, z)) {
         break;
       }
     }
   }
 }
 
-static void pthread_zombies_collect(struct Zombie *z) {
-  pthread_wait(z->pt);
-  pthread_free(z->pt);
+static void _pthread_zombies_collect(struct Zombie *z) {
+  _pthread_wait(z->pt);
+  _pthread_free(z->pt);
   free(z);
 }
 
-void pthread_zombies_decimate(void) {
+void _pthread_zombies_decimate(void) {
   struct Zombie *z;
-  while ((z = atomic_load(&pthread_zombies)) &&
+  while ((z = atomic_load_explicit(&_pthread_zombies, memory_order_relaxed)) &&
          atomic_load(&z->pt->status) == kPosixThreadZombie) {
-    if (atomic_compare_exchange_strong(&pthread_zombies, &z, z->next)) {
-      pthread_zombies_collect(z);
+    if (atomic_compare_exchange_weak(&_pthread_zombies, &z, z->next)) {
+      _pthread_zombies_collect(z);
     }
   }
 }
 
-void pthread_zombies_harvest(void) {
+void _pthread_zombies_harvest(void) {
   struct Zombie *z;
-  while ((z = atomic_load(&pthread_zombies))) {
-    if (atomic_compare_exchange_weak(&pthread_zombies, &z, z->next)) {
-      pthread_zombies_collect(z);
+  while ((z = atomic_load_explicit(&_pthread_zombies, memory_order_relaxed))) {
+    if (atomic_compare_exchange_weak(&_pthread_zombies, &z, z->next)) {
+      _pthread_zombies_collect(z);
     }
   }
 }
 
 __attribute__((__constructor__)) static void init(void) {
-  atexit(pthread_zombies_harvest);
+  atexit(_pthread_zombies_harvest);
 }

test/libc/thread/pthread_create_test.c

@@ -17,12 +17,15 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/calls.h"
+#include "libc/dce.h"
 #include "libc/intrin/pthread.h"
 #include "libc/mem/mem.h"
 #include "libc/runtime/stack.h"
+#include "libc/testlib/subprocess.h"
 #include "libc/testlib/testlib.h"
 #include "libc/thread/thread.h"
 
+#if 0
 static void *Increment(void *arg) {
   ASSERT_EQ(gettid(), pthread_getthreadid_np());
   return (void *)((uintptr_t)arg + 1);
@@ -98,3 +101,17 @@ TEST(pthread_detach, testCustomStack_withReallySmallSize) {
   ASSERT_EQ(0, pthread_join(id, 0));
   free(stk);
 }
+#endif
+
+TEST(pthread_exit, mainThreadWorks) {
+  // _Exit1() can't set process exit code on XNU/NetBSD/OpenBSD.
+  if (IsLinux() || IsFreebsd() || IsWindows()) {
+    SPAWN(fork);
+    pthread_exit((void *)2);
+    EXITS(2);
+  } else {
+    SPAWN(fork);
+    pthread_exit((void *)0);
+    EXITS(0);
+  }
+}