allow adding runDependencies in preRun

4 files changed, 32 insertions, 0 deletions

diff --git a/src/postamble.js b/src/postamble.js
index cf863669..24b8e4a1 100644
--- a/src/postamble.js
+++ b/src/postamble.js
@@ -38,6 +38,11 @@ function run(args) {
 
   if (Module['preRun']) {
     Module['preRun']();
+    if (runDependencies > 0) {
+      // preRun added a dependency, run will be called later
+      Module['preRun'] = null;
+      return 0;
+    }
   }
 
   var ret = null;
diff --git a/src/preamble.js b/src/preamble.js
index e9ba2009..997e5ab3 100644
--- a/src/preamble.js
+++ b/src/preamble.js
@@ -854,6 +854,9 @@ var STRING_TABLE = [];
 // do asynchronous work before running, increment this and
 // decrement it. Incrementing must happen in a place like
 // PRE_RUN_ADDITIONS (used by emcc to add file preloading).
+// Note that you can add dependencies in preRun, even though
+// it happens right before run - run will be postponed until
+// the dependencies are met.
 var runDependencies = 0;
 function addRunDependency() {
   runDependencies++;
diff --git a/tests/pre_run_deps.cpp b/tests/pre_run_deps.cpp
new file mode 100644
index 00000000..41c06972
--- /dev/null
+++ b/tests/pre_run_deps.cpp
@@ -0,0 +1,10 @@
+#include <stdio.h>
+#include <emscripten.h>
+
+int main() {
+  printf("main() called.\n");
+  int result = emscripten_run_script_int("Module.okk");
+  REPORT_RESULT();
+  return 1;
+}
+
diff --git a/tests/runner.py b/tests/runner.py
index f44dc95a..a1a3425a 100755
--- a/tests/runner.py
+++ b/tests/runner.py
@@ -7299,6 +7299,20 @@ elif 'browser' in str(sys.argv):
     def test_cubegeom_color2(self):
       self.btest('cubegeom_color2.c', expected='1121999515')
 
+    def test_pre_run_deps(self):
+      # Adding a dependency in preRun will delay run
+      open(os.path.join(self.get_dir(), 'pre.js'), 'w').write('''
+        Module.preRun = function() {
+          addRunDependency();
+          Module.print('preRun called, added a dependency...');
+          setTimeout(function() {
+            Module.okk = 10;
+            removeRunDependency()
+          }, 2000);
+        };
+      ''')
+      self.btest('pre_run_deps.cpp', expected='10', args=['--pre-js', 'pre.js'])
+
 elif 'benchmark' in str(sys.argv):
   # Benchmarks. Run them with argument |benchmark|. To run a specific test, do
   # |benchmark.test_X|.