Remove non-working emscripten_fetch_wait / EMSCRIPTEN_FETCH_WAITABLE.…

… NFC (#22138) This API hasn't worked since the fastcomp days, so I think its probably better to remove/deprecate it rather than try to make it work (perhaps using pthreads).
emscripten-core · Jun 24, 2024 · d079eca · d079eca
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diff --git a/ChangeLog.md b/ChangeLog.md
@@ -20,6 +20,9 @@ See docs/process.md for more on how version tagging works.
 
 3.1.62 (in development)
 -----------------------
+- The `EMSCRIPTEN_FETCH_WAITABLE` flag along with the `emscripten_fetch_wait`
+  API were marked a deprecated.  These feature have not functions for several
+  years now. (#22138)
 - The internal `read_` function was removed.  We now just use `readBinary` or
   `readAsync`. (#22080)
 - reference-types feature is now enabled by default in Emscripten, due to the

diff --git a/site/source/docs/api_reference/fetch.rst b/site/source/docs/api_reference/fetch.rst
@@ -200,55 +200,8 @@ emscripten_fetch() returns.
   - ``--proxy-to-worker`` + ``-pthread``: Synchronous Synchronous Fetch operations
     are available both on the main thread and pthreads.
 
-Waitable Fetches
-================
-
-Emscripten Fetch operations can also run in a third mode, called a *waitable*
-fetch. Waitable fetches start off as asynchronous, but at any point after the
-fetch has started, the calling thread can issue a wait operation to either wait
-for the completion of the fetch, or to just poll whether the fetch operation has
-yet completed. The following code sample illustrates how this works.
-
-.. code-block:: cpp
-
-  int main() {
-    emscripten_fetch_attr_t attr;
-    emscripten_fetch_attr_init(&attr);
-    strcpy(attr.requestMethod, "GET");
-    attr.attributes = EMSCRIPTEN_FETCH_LOAD_TO_MEMORY | EMSCRIPTEN_FETCH_WAITABLE;
-    emscripten_fetch_t *fetch = emscripten_fetch(&attr, "file.dat"); // Starts as asynchronous.
-
-    EMSCRIPTEN_RESULT ret = EMSCRIPTEN_RESULT_TIMED_OUT;
-    while(ret == EMSCRIPTEN_RESULT_TIMED_OUT) {
-      /* possibly do some other work; */
-      ret = emscripten_fetch_wait(fetch, 0/*milliseconds to wait, 0 to just poll, INFINITY=wait until completion*/);
-    }
-    // The operation has finished, safe to examine the fields of the 'fetch' pointer now.
-
-    if (fetch->status == 200) {
-      printf("Finished downloading %llu bytes from URL %s.\n", fetch->numBytes, fetch->url);
-      // The data is now available at fetch->data[0] through fetch->data[fetch->numBytes-1];
-    } else {
-      printf("Downloading %s failed, HTTP failure status code: %d.\n", fetch->url, fetch->status);
-    }
-    emscripten_fetch_close(fetch);
-  }
-
-Waitable fetches allow interleaving multiple tasks in one thread so that the
-issuing thread can perform some other work until the fetch completes.
-
-.. note::
-
-  Waitable fetches are available only in certain build modes:
-
-  - **No flags** or ``--proxy-to-worker``: Waitable fetches are not available.
-  - ``-pthread``: Waitable fetches are available on pthreads, but not
-    on the main thread.
-  - ``--proxy-to-worker`` + ``-pthread``: Waitable fetches are
-    available on all threads.
-
 Tracking Progress
-====================
+=================
 
 For robust fetch management, there are several fields available to track the
 status of an XHR.

diff --git a/src/generated_struct_info32.json b/src/generated_struct_info32.json
@@ -1488,9 +1488,8 @@
             "withCredentials": 60
         },
         "emscripten_fetch_t": {
-            "__attributes": 112,
-            "__proxyState": 108,
-            "__size__": 208,
+            "__attributes": 108,
+            "__size__": 200,
             "data": 12,
             "dataOffset": 24,
             "id": 0,

diff --git a/src/generated_struct_info64.json b/src/generated_struct_info64.json
@@ -1489,7 +1489,6 @@
         },
         "emscripten_fetch_t": {
             "__attributes": 128,
-            "__proxyState": 124,
             "__size__": 272,
             "data": 24,
             "dataOffset": 40,

diff --git a/src/struct_info.json b/src/struct_info.json
@@ -1101,7 +1101,6 @@
                 "readyState",
                 "status",
                 "statusText",
-                "__proxyState",
                 "__attributes"
             ]
         },

diff --git a/system/include/emscripten/fetch.h b/system/include/emscripten/fetch.h
@@ -61,9 +61,8 @@ extern "C" {
 // emscripten_fetch() while the operation is in progress.
 #define EMSCRIPTEN_FETCH_SYNCHRONOUS 64
 
-// If specified, it will be possible to call emscripten_fetch_wait() on the
-// fetch to test or wait for its completion.
 #define EMSCRIPTEN_FETCH_WAITABLE 128
+#pragma clang deprecated(EMSCRIPTEN_FETCH_WAITABLE, "waitable fetch requests are no longer implemented")
 
 struct emscripten_fetch_t;
 
@@ -190,8 +189,6 @@ typedef struct emscripten_fetch_t {
   // Specifies a human-readable form of the status code.
   char statusText[64];
 
-  _Atomic uint32_t __proxyState;
-
   // For internal use only.
   emscripten_fetch_attr_t __attributes;
 } emscripten_fetch_t;
@@ -204,14 +201,7 @@ void emscripten_fetch_attr_init(emscripten_fetch_attr_t * _Nonnull fetch_attr);
 // given URL or from IndexedDB database.
 emscripten_fetch_t *emscripten_fetch(emscripten_fetch_attr_t * _Nonnull fetch_attr, const char * _Nonnull url);
 
-// Synchronously blocks to wait for the given fetch operation to complete. This
-// operation is not allowed in the main browser thread, in which case it will
-// return EMSCRIPTEN_RESULT_NOT_SUPPORTED. Pass timeoutMSecs=infinite to wait
-// indefinitely. If the wait times out, the return value will be
-// EMSCRIPTEN_RESULT_TIMED_OUT.
-// The onsuccess()/onerror()/onprogress() handlers will be called in the calling
-// thread from within this function before this function returns.
-EMSCRIPTEN_RESULT emscripten_fetch_wait(emscripten_fetch_t * _Nonnull fetch, double timeoutMSecs);
+EMSCRIPTEN_RESULT emscripten_fetch_wait(emscripten_fetch_t * _Nonnull fetch, double timeoutMSecs) __attribute__((deprecated));
 
 // Closes a finished or an executing fetch operation and frees up all memory. If
 // the fetch operation was still executing, the onerror() handler will be called

diff --git a/system/lib/fetch/emscripten_fetch.c b/system/lib/fetch/emscripten_fetch.c
@@ -147,67 +147,14 @@ emscripten_fetch_t* emscripten_fetch(emscripten_fetch_attr_t* fetch_attr, const
 }
 
 EMSCRIPTEN_RESULT emscripten_fetch_wait(emscripten_fetch_t* fetch, double timeoutMsecs) {
-#if __EMSCRIPTEN_PTHREADS__
-  if (!fetch) {
-    return EMSCRIPTEN_RESULT_INVALID_PARAM;
-  }
-  uint32_t proxyState = fetch->__proxyState;
-  if (proxyState == 2) {
-    // already finished.
-    return EMSCRIPTEN_RESULT_SUCCESS;
-  }
-  if (proxyState != 1) {
-    // the fetch should be ongoing?
-    return EMSCRIPTEN_RESULT_INVALID_PARAM;
-  }
-#ifdef FETCH_DEBUG
-  emscripten_dbg("fetch: emscripten_fetch_wait..");
-#endif
-  if (timeoutMsecs <= 0) {
-    return EMSCRIPTEN_RESULT_TIMED_OUT;
-  }
-  while (proxyState == 1 /*sent to proxy worker*/) {
-    if (emscripten_is_main_browser_thread()) {
-      emscripten_err("fetch: emscripten_fetch_wait failed: main thread cannot block to wait for long periods of time! Migrate the application to run in a worker to perform synchronous file IO, or switch to using asynchronous IO.");
-      return EMSCRIPTEN_RESULT_FAILED;
-    }
-    int ret = emscripten_futex_wait(&fetch->__proxyState, proxyState, timeoutMsecs);
-    if (ret == -ETIMEDOUT) {
-      return EMSCRIPTEN_RESULT_TIMED_OUT;
-    }
-    proxyState = fetch->__proxyState;
-  }
-#ifdef FETCH_DEBUG
-  emscripten_dbg("fetch: emscripten_fetch_wait done..");
-#endif
-
-  if (proxyState != 2) {
-    return EMSCRIPTEN_RESULT_FAILED;
-  }
-  return EMSCRIPTEN_RESULT_SUCCESS;
-#else
-  if (fetch->readyState >= STATE_DONE) {
-    return EMSCRIPTEN_RESULT_SUCCESS; // already finished.
-  }
-  if (timeoutMsecs == 0) {
-    return EMSCRIPTEN_RESULT_TIMED_OUT /*Main thread testing completion with sleep=0msecs*/;
-  } else {
-#ifdef FETCH_DEBUG
-    emscripten_err("fetch: emscripten_fetch_wait() cannot stop to wait when building without pthreads!");
-#endif
-    return EMSCRIPTEN_RESULT_FAILED /*Main thread cannot block to wait*/;
-  }
-#endif
+  return EMSCRIPTEN_RESULT_FAILED;
 }
 
 EMSCRIPTEN_RESULT emscripten_fetch_close(emscripten_fetch_t* fetch) {
   if (!fetch) {
     return EMSCRIPTEN_RESULT_SUCCESS; // Closing null pointer is ok, same as with free().
   }
 
-#if __EMSCRIPTEN_PTHREADS__
-  fetch->__proxyState = 0;
-#endif
   // This function frees the fetch pointer so that it is invalid to access it anymore.
   // Use a few key fields as an integrity check that we are being passed a good pointer to a valid
   // fetch structure, which has not been yet closed. (double close is an error)

diff --git a/test/fetch/test_fetch_sync_in_main_thread.c b/test/fetch/test_fetch_sync_in_main_thread.c
diff --git a/test/fetch/test_fetch_waitable.c b/test/fetch/test_fetch_waitable.c
diff --git a/test/test_browser.py b/test/test_browser.py
@@ -4657,12 +4657,6 @@ def test_fetch_sync_xhr_in_proxy_to_worker(self):
     self.btest_exit('fetch/test_fetch_sync_xhr.cpp',
                     args=['-sFETCH_DEBUG', '-sFETCH', '--proxy-to-worker'])
 
-  # Tests waiting on EMSCRIPTEN_FETCH_WAITABLE request from a worker thread
-  @unittest.skip("emscripten_fetch_wait relies on an asm.js-based web worker")
-  def test_fetch_sync_fetch_in_main_thread(self):
-    shutil.copyfile(test_file('gears.png'), 'gears.png')
-    self.btest_exit('fetch/test_fetch_sync_in_main_thread.cpp', args=['-sFETCH_DEBUG', '-sFETCH', '-sWASM=0', '-pthread', '-sPROXY_TO_PTHREAD'])
-
   @disabled('https://github.com/emscripten-core/emscripten/issues/16746')
   def test_fetch_idb_store(self):
     self.btest_exit('fetch/test_fetch_idb_store.cpp', args=['-pthread', '-sFETCH', '-sPROXY_TO_PTHREAD'])
@@ -4692,11 +4686,6 @@ def test_fetch_stream_async(self):
     create_file('myfile.dat', 'hello world\n' * 1000)
     self.btest_exit('fetch/test_fetch_stream_async.c', args=['-sFETCH'])
 
-  @disabled('waitable fetch operations were disabled when the fetch worker was removed')
-  def test_fetch_waitable(self):
-    create_file('myfile.dat', 'hello world\n' * 1000)
-    self.btest_exit('fetch/test_fetch_waitable.c', args=['-sFETCH'])
-
   def test_fetch_persist(self):
     create_file('myfile.dat', 'hello world\n')
     self.btest_exit('fetch/test_fetch_persist.c', args=['-sFETCH'])

diff --git a/test/test_other.py b/test/test_other.py
@@ -13568,7 +13568,6 @@ def test_build_fetch_tests(self):
     self.build(test_file('fetch/test_fetch_idb_store.c'))
     self.build(test_file('fetch/test_fetch_stream_async.c'))
     self.build(test_file('fetch/test_fetch_sync.c'))
-    self.build(test_file('fetch/test_fetch_waitable.c'))
     self.build(test_file('fetch/test_fetch_progress.c'))
 
   def test_fetch_init_node(self):