Merge pull request emscripten-core#16 from rstz/fix-early-syscalls

Fix early syscall use by adding a Clang attribute.

pthreadfs/README.md

@@ -73,7 +73,7 @@ See `pthreadfs/examples/emscripten-tests/fsafs.cpp` for exemplary usage.
 - Some functionality of the Emscripten File System API is missing, such as sockets, IndexedDB integration and support for XHRequests.
 - PThreadFS depends on C++ libraries. `EM_PTHREADFS_ASM()` cannot be used within C files.
 - Performance is good if and only if optimizations (compiler option `-O2`) are enabled and DevTools are closed.
-- Accessing the file system before `main()` is called may not work. 
+- Accessing the file system before `main()` requires linker option `PTHREAD_POOL_SIZE=<expression>` to be active. Doing so may lead to some blocking of the main thread, which is risky. Check out `examples/early_syscall.cpp` for an example.
 - The Storage Foundation backend requires case-insensitive file names.
 - Compiling with the Closure Compiler is not supported.
 - Compiling with optimization `-O3` is not yet supported and may lead to a faulty build.

pthreadfs/examples/emscripten-tests/FAIL_early_stat64.cpp → pthreadfs/examples/emscripten-tests/early_syscall.cpp

@@ -19,7 +19,7 @@ int main() {
 class EarlyObject {
  public:
   EarlyObject() {
-    puts("This test is a warning: Do not use syscalls in objects before main is called!");
+    puts("This test will fail unless compiled with PTHREAD_POOL_SIZE=2 (or higher).");
     puts("Start constructing EarlyObject.");
     int err;
     struct stat s;

pthreadfs/pthreadfs.cpp

@@ -311,7 +311,7 @@ SYS_CAPI_DEF(
 
 // Define global variables to be populated by resume;
 std::function<void()> g_resumeFct;
-emscripten::sync_to_async g_sync_to_async_helper;
+emscripten::sync_to_async g_sync_to_async_helper __attribute__((init_priority(102)));
 
 // Other helper code