Enable file locking in musl stdio

This is second attempt at landing a version of
d5d5f69

The first time we tried it #13837 we ran into issues with
test_pthread_exit_process deadlocking which I tracked down to an issue
with `system/lib/libc/musl/src/thread/__wait.c` where it was blocking
the main thread forever rather then looping and calling
`emscripten_main_thread_process_queued_calls`.

Includes a version of #14481 so that should land before this does.

Fixes: #13194

system/lib/libc/musl/src/thread/__wait.c

@@ -1,10 +1,13 @@
 #ifdef __EMSCRIPTEN__
 #include <math.h>
+#include <emscripten/threading.h>
 #endif
 
 #include "pthread_impl.h"
 
+#ifdef __EMSCRIPTEN__
 int _pthread_isduecanceled(struct pthread *pthread_ptr);
+#endif
 
 void __wait(volatile int *addr, volatile int *waiters, int val, int priv)
 {
@@ -18,7 +21,7 @@ void __wait(volatile int *addr, volatile int *waiters, int val, int priv)
 #ifdef __EMSCRIPTEN__
 	int is_main_thread = emscripten_is_main_runtime_thread();
 	while (*addr==val) {
-		if (pthread_self()->cancelasync == PTHREAD_CANCEL_ASYNCHRONOUS) {
+		if (is_main_thread || pthread_self()->cancelasync == PTHREAD_CANCEL_ASYNCHRONOUS) {
 			// Must wait in slices in case this thread is cancelled in between.
 			int e;
 			do {

system/lib/pthread/pthread_create.c

@@ -7,6 +7,7 @@
 
 #define _GNU_SOURCE
 #include "pthread_impl.h"
+#include "stdio_impl.h"
 #include "assert.h"
 #include <pthread.h>
 #include <stdbool.h>
@@ -53,6 +54,15 @@ void __do_cleanup_pop(struct __ptcb *cb) {
   __pthread_self()->cancelbuf = cb->__next;
 }
 
+static FILE *volatile dummy_file = 0;
+weak_alias(dummy_file, __stdin_used);
+weak_alias(dummy_file, __stdout_used);
+weak_alias(dummy_file, __stderr_used);
+
+static void init_file_lock(FILE *f) {
+  if (f && f->lock<0) f->lock = 0;
+}
+
 int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict attrp, void *(*entry)(void *), void *restrict arg) {
   // Note on LSAN: lsan intercepts/wraps calls to pthread_create so any
   // allocation we we do here should be considered leaks.
@@ -61,6 +71,17 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att
     return EINVAL;
   }
 
+  pthread_t self = __pthread_self();
+  if (!libc.threaded) {
+    for (FILE *f=*__ofl_lock(); f; f=f->next)
+      init_file_lock(f);
+    __ofl_unlock();
+    init_file_lock(__stdin_used);
+    init_file_lock(__stdout_used);
+    init_file_lock(__stderr_used);
+    libc.threaded = 1;
+  }
+
   // Allocate thread block (pthread_t structure).
   struct pthread *new = malloc(sizeof(struct pthread));
   // zero-initialize thread structure.

tests/core/test_stdio_locking.c

@@ -0,0 +1,55 @@
+/*
+ * Regression test for stdio locking.  If file locking is not enabled the
+ * threads will race to write the file output buffer and we will see lines
+ * that are longer or shorter then 100 characters.  When locking is
+ * working/enabled each 100 charactor line will be printed seperately.
+ *
+ * See:
+ *   musl/src/stdio/__lockfile.c
+ *   musl/src/stdio/fwrite.c
+ */
+#include <assert.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+
+pthread_t thread[2];
+
+char *char_repeat(int n, char c) {
+  char *dest = malloc(n + 1);
+  memset(dest, c, n);
+  dest[n] = '\0';
+  return dest;
+}
+
+void *thread_main(void *arg) {
+  char *msg = char_repeat(100, 'a');
+  for (int i = 0; i < 10; ++i)
+  printf("%s\n", msg);
+  free(msg);
+  return 0;
+}
+
+int main() {
+  printf("in main\n");
+  void *thread_rtn;
+  int rc;
+
+  rc = pthread_create(&thread[0], NULL, thread_main, NULL);
+  assert(rc == 0);
+
+  rc = pthread_create(&thread[1], NULL, thread_main, NULL);
+  assert(rc == 0);
+
+  rc = pthread_join(thread[0], &thread_rtn);
+  assert(rc == 0);
+  assert(thread_rtn == 0);
+
+  rc = pthread_join(thread[1], &thread_rtn);
+  assert(rc == 0);
+  assert(thread_rtn == 0);
+
+  printf("main done\n");
+  return 0;
+}

tests/core/test_stdio_locking.out

@@ -0,0 +1,22 @@
+in main
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+main done

tests/other/metadce/minimal_main_Oz_USE_PTHREADS_PROXY_TO_PTHREAD.exports

@@ -14,7 +14,7 @@ M
 N
 O
 P
-v
+Q
 w
 x
 y

tests/other/metadce/minimal_main_Oz_USE_PTHREADS_PROXY_TO_PTHREAD.funcs

@@ -1,11 +1,14 @@
 $GetQueue
 $__emscripten_init_main_thread
+$__emscripten_stdout_seek
 $__errno_location
 $__pthread_mutex_lock
 $__pthread_mutex_trylock
 $__pthread_mutex_unlock
 $__pthread_self_internal
 $__pthread_setcancelstate
+$__stdio_write
+$__wasi_syscall_ret
 $__wasm_call_ctors
 $__wasm_init_memory
 $_do_call
@@ -34,9 +37,11 @@ $emscripten_sync_run_in_main_thread
 $emscripten_sync_run_in_main_thread
 $emscripten_tls_init
 $free_tls
+$init_file_lock
 $init_mparams
 $main
 $memset
+$pthread_mutexattr_destroy
 $sbrk
 $stackAlloc
 $stackRestore

tests/other/metadce/minimal_main_Oz_USE_PTHREADS_PROXY_TO_PTHREAD.imports

@@ -19,3 +19,4 @@ a.r
 a.s
 a.t
 a.u
+a.v

tests/other/metadce/minimal_main_Oz_USE_PTHREADS_PROXY_TO_PTHREAD.sent

@@ -19,3 +19,4 @@ r
 s
 t
 u
+v

tests/other/metadce/minimal_main_Oz_USE_PTHREADS_PROXY_TO_PTHREAD.size

@@ -1 +1 @@
-16368
+16977

tests/test_core.py

@@ -8406,6 +8406,12 @@ def test_emscripten_futexes(self):
     self.set_setting('USE_PTHREADS')
     self.do_run_in_out_file_test('core/pthread/emscripten_futexes.c')
 
+  @node_pthreads
+  def test_stdio_locking(self):
+    self.set_setting('PTHREAD_POOL_SIZE', '2')
+    self.set_setting('EXIT_RUNTIME')
+    self.do_run_in_out_file_test('core', 'test_stdio_locking.c')
+
   @needs_dylink
   @node_pthreads
   def test_pthread_dylink_basics(self):

tools/system_libs.py

@@ -1299,7 +1299,7 @@ class CompilerRTLibrary(Library):
   force_object_files = True
 
 
-class libc_rt_wasm(OptimizedAggressivelyForSizeLibrary, AsanInstrumentedLibrary, CompilerRTLibrary, MuslInternalLibrary):
+class libc_rt_wasm(OptimizedAggressivelyForSizeLibrary, AsanInstrumentedLibrary, CompilerRTLibrary, MuslInternalLibrary, MTLibrary):
   name = 'libc_rt_wasm'
 
   def get_files(self):