Add a testcase for pthreads race conditions

tests/pthread/test_pthread_proxy_hammer.cpp

@@ -0,0 +1,75 @@
+#include <errno.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <emscripten.h>
+#include <stdio.h>
+
+class random_device
+{
+    int __f_;
+public:
+    // constructors
+    explicit random_device();
+    ~random_device();
+
+    // generating functions
+    unsigned operator()();
+};
+
+random_device::random_device()
+{
+    __f_ = open("/dev/urandom", O_RDONLY);
+    if (__f_ < 0) abort();
+}
+
+random_device::~random_device()
+{
+    close(__f_);
+}
+
+unsigned
+random_device::operator()()
+{
+    unsigned r;
+    size_t n = sizeof(r);
+    char* p = reinterpret_cast<char*>(&r);
+    while (n > 0)
+    {
+        ssize_t s = read(__f_, p, 1);
+        if (s == 0) abort();
+        if (s == -1)
+        {
+            if (errno != EINTR) abort();
+            continue;
+        }
+        n -= static_cast<size_t>(s);
+        p += static_cast<size_t>(s);
+    }
+    return r;
+}
+
+int main() {
+  int total = 0;
+  for (int i = 0; i < 1024; i++) {
+    // printf causes proxying
+    printf("%d %d\n", i, total);
+    for (int j = 0; j < 1024; j++) {
+      // allocation uses a mutex
+      auto* rd = new random_device();
+      // reading data causes proxying
+      for (int k = 0; k < 4; k++) {
+        total += (*rd)();
+      }
+      // make sure the optimizer doesn't remove the allocation
+      EM_ASM({ out("iter") }, rd);
+      delete rd;
+    }
+  }
+  printf("done: %d", total);
+#ifdef REPORT_RESULT
+	REPORT_RESULT(0);
+#endif
+  return 0;
+}
+

tests/runner.py

@@ -1364,12 +1364,12 @@ def assert_out_queue_empty(self, who):
         self.harness_out_queue.get()
       raise Exception('excessive responses from %s' % who)
 
-  # @param tries_left: how many more times to try this test, if it fails. browser tests have
-  #                    many more causes of flakiness (in particular, they do not run
-  #                    synchronously, so we have a timeout, which can be hit if the VM
-  #                    we run on stalls temporarily), so we let each test try more than
-  #                    once by default
-  def run_browser(self, html_file, message, expectedResult=None, timeout=None, tries_left=1):
+  # @param extra_tries: how many more times to try this test, if it fails. browser tests have
+  #                     many more causes of flakiness (in particular, they do not run
+  #                     synchronously, so we have a timeout, which can be hit if the VM
+  #                     we run on stalls temporarily), so we let each test try more than
+  #                     once by default
+  def run_browser(self, html_file, message, expectedResult=None, timeout=None, extra_tries=1):
     if not has_browser():
       return
     if BrowserCore.unresponsive_tests >= BrowserCore.MAX_UNRESPONSIVE_TESTS:
@@ -1408,10 +1408,10 @@ def run_browser(self, html_file, message, expectedResult=None, timeout=None, tri
           try:
             self.assertIdenticalUrlEncoded(expectedResult, output)
           except Exception as e:
-            if tries_left > 0:
+            if extra_tries > 0:
               print('[test error (see below), automatically retrying]')
               print(e)
-              return self.run_browser(html_file, message, expectedResult, timeout, tries_left - 1)
+              return self.run_browser(html_file, message, expectedResult, timeout, extra_tries - 1)
             else:
               raise e
       finally:
@@ -1549,7 +1549,7 @@ def btest(self, filename, expected=None, reference=None, force_c=False,
             reference_slack=0, manual_reference=False, post_build=None,
             args=[], outfile='test.html', message='.', also_proxied=False,
             url_suffix='', timeout=None, also_asmjs=False,
-            manually_trigger_reftest=False):
+            manually_trigger_reftest=False, extra_tries=1):
     assert expected or reference, 'a btest must either expect an output, or have a reference image'
     # if we are provided the source and not a path, use that
     filename_is_src = '\n' in filename
@@ -1583,7 +1583,7 @@ def btest(self, filename, expected=None, reference=None, force_c=False,
       post_build()
     if not isinstance(expected, list):
       expected = [expected]
-    self.run_browser(outfile + url_suffix, message, ['/report_result?' + e for e in expected], timeout=timeout)
+    self.run_browser(outfile + url_suffix, message, ['/report_result?' + e for e in expected], timeout=timeout, extra_tries=extra_tries)
 
     # Tests can opt into being run under asmjs as well
     if 'WASM=0' not in args and (also_asmjs or self.also_asmjs):

tests/test_browser.py

@@ -4911,3 +4911,18 @@ def test_zzz_zzz_4GB_fail(self):
     # 4GB.
     self.emcc_args += ['-O2', '-s', 'ALLOW_MEMORY_GROWTH', '-s', 'MAXIMUM_MEMORY=4GB', '-s', 'ABORTING_MALLOC=0']
     self.do_run_in_out_file_test('tests', 'browser', 'test_4GB_fail.cpp', js_engines=[V8_ENGINE])
+
+  @unittest.skip("only run this manually, to test for race conditions")
+  @requires_threads
+  def test_manual_pthread_proxy_hammer(self):
+    # the specific symptom of the hangs that were fixed is that the test hangs
+    # at some point, using 0% CPU. often that occured in 0-200 iterations out
+    # of the 1024 the test runs by default, but this can vary by machine and
+    # browser...
+    self.btest(path_from_root('tests', 'pthread', 'test_pthread_proxy_hammer.cpp'),
+               expected='0',
+               args=['-s', 'USE_PTHREADS=1', '-O2', '-s', 'PROXY_TO_PTHREAD'],
+               timeout=10000,
+               # don't run this with the default extra_tries value, as this is
+               # *meant* to notice something random, a race condition.
+               extra_tries=0)