Merge pull request emscripten-core#5 from rstz/multiple-backend-support

Add support for multiple storage backends

pthreadfs/README.md

@@ -5,6 +5,8 @@ The Emscripten Pthread File System (PThreadFS) unlocks using (partly) asynchrono
 PThreadFS works by replacing Emscripten's file system API with a new API that proxies all file system operations to a dedicated pthread. This dedicated thread maintains a virtual file system that can use different APIs as backend (very similar to the way Emscripten's VFS is designed). In particular, PThreadFS comes with built-in support for asynchronous backends such as [OPFS Access Handles](https://docs.google.com/document/d/121OZpRk7bKSF7qU3kQLqAEUVSNxqREnE98malHYwWec/edit#heading=h.gj2fudnvy982).
 Although the underlying storage API is asynchronous, PThreadFS makes it appear synchronous to the C++ application.
 
+If OPFS Access Handles are not available, PThreadFS will attempt to use the [Storage Foundation API](https://github.com/WICG/storage-foundation-api-explainer). As a last fallback, Emscripten's MEMFS in-memory file system is used.
+
 The code is still prototype quality and **should not be used in a production environment** for the time being.
 
 ## Enable and detect OPFS in Chrome
@@ -69,7 +71,7 @@ In order to use the code in a new project, you only need the three files in the
 #include "pthreadfs.h"
 ```
 - Call `emscripten_init_pthreadfs();` at the top of `main()` (or before any file system syscalls).
-- PThreadFS maintains a virtual file system. The OPFS backend is mounted at `/filesystemaccess/`. Only files in this folder are persisted between sessions. All other files will be stored in-memory through MEMFS.
+- PThreadFS maintains a virtual file system. The OPFS backend is mounted at `/pthreadfs/`. Only files in this folder are persisted between sessions. All other files will be stored in-memory through MEMFS.
 
 ### Build process changes
 
@@ -102,8 +104,8 @@ See `pthreadfs/examples/emscripten-tests/fsafs.cpp` for exemplary usage.
 
 ## Known Limitations
 
-- All files to be stored using the file system access Access Handles must be stored in the `/filesystemaccess` folder.
-- Files in the `/filesystemaccess` folder cannot interact through syscalls with other files (e.g. moving, copying, etc.).
+- All files to be stored using the file system access Access Handles must be stored in the `/pthreadfs` folder.
+- Files in the `/pthreadfs` folder cannot interact through syscalls with other files (e.g. moving, copying, etc.).
 - The code is still prototype quality and **should not be used in a production environment** yet. It is possible that the use of PThreadFS might lead to subtle bugs in other libraries.
 - PThreadFS requires PROXY_TO_PTHREAD to be active. In particular, no system calls interacting with the file system should be called from the main thread.
 - Some functionality of the Emscripten File System API is missing, such as sockets, IndexedDB integration and support for XHRequests.

pthreadfs/examples/emscripten-tests/fsafs.cpp

@@ -7,32 +7,31 @@
 
 int main () {
   emscripten_init_pthreadfs();
-  std::cout << "std::cout works fine.\n";
+  std::cout << "Proof that stdout works fine.\n";
   std::ofstream myfile;
-  myfile.open ("filesystemaccess/example");
-  myfile << "Writing a few characters to the example file.\n";
+  myfile.open ("pthreadfs/example");
+  myfile << "Writing a few characters.\n";
   myfile.close();
 
   std::string line;
-  std::ifstream myfile_read ("filesystemaccess/example");
+  std::ifstream myfile_read ("pthreadfs/example");
 
   if (myfile_read.is_open()) {
     std::getline(myfile_read, line);
-    EM_ASM({
-      console.log("Read line " + UTF8ToString($0));
+    EM_ASM({console.log("Read line" + UTF8ToString($0));
     }, line.c_str());
     myfile_read.close();
   }
 
-  std::ofstream stream1 ("filesystemaccess/multistreamexample");
-  std::ofstream stream2 ("filesystemaccess/multistreamexample");
+  std::ofstream stream1 ("pthreadfs/multistreamexample");
+  std::ofstream stream2 ("pthreadfs/multistreamexample");
   stream1 << "Write a line through stream1.\n";
   stream2 << "Write a line through stream2.\n";
   stream1.close();
   stream2.close();
 
-  std::remove("filesystemaccess/multistreamexample"); 
-  bool can_open_deleted_file = (bool) std::ifstream("filesystemaccess/multistreamexample");
+  std::remove("pthreadfs/multistreamexample"); 
+  bool can_open_deleted_file = (bool) std::ifstream("pthreadfs/multistreamexample");
   if(!can_open_deleted_file) { 
     std::cout << "Opening deleted file failed, as expected.\n"; 
   }

pthreadfs/examples/emscripten-tests/multiple_threads.cpp

@@ -11,7 +11,7 @@
 void threadMain(int msg) {
   size_t thread_id = std::hash<std::thread::id>{}(std::this_thread::get_id());
   std::ofstream myfile;
-  myfile.open ("filesystemaccess/multi_threading_example", std::ios_base::app);
+  myfile.open ("pthreadfs/multi_threading_example", std::ios_base::app);
   myfile << "Writing from thread " << msg << " Id: " << thread_id << "   ";
   myfile.close();
   EM_ASM({console.log(`Wrote on thread ${$0}`);}, thread_id);
@@ -21,7 +21,7 @@ void threadMain(int msg) {
 int main () {
   emscripten_init_pthreadfs();
   EM_ASM({console.log("Hello from main")});
-  std::remove("filesystemaccess/multi_threading_example"); 
+  std::remove("pthreadfs/multi_threading_example"); 
 
   constexpr int number_of_threads = 10;
 
@@ -35,7 +35,7 @@ int main () {
   }
 
   std::ofstream myfile;
-  myfile.open ("filesystemaccess/multi_threading_example");
+  myfile.open ("pthreadfs/multi_threading_example");
   myfile << "Writing the main thread.\n";
   myfile.close();
 

pthreadfs/examples/sqlite-speedtest/sqlite-speedtest-prejs.js

@@ -3,4 +3,4 @@ var Module = Module || {};
 Module['arguments'] = Module['arguments'] || [];
 Module['arguments'].push('--size');
 Module['arguments'].push('40');
-Module['arguments'].push(`/filesystemaccess/db${Math.random()}`);
+Module['arguments'].push(`/pthreadfs/db${Math.random()}`);