PPAPI: Make blocking completion callbacks work.

ppapi/thunk/enter.cc

Index: ppapi/thunk/enter.cc
diff --git a/ppapi/thunk/enter.cc b/ppapi/thunk/enter.cc
index a5117118c2e41f06a202fa5057d196cd84337e61..978d95a8da2d3be64251fbf9d21020ee4e1ebfcc 100644
--- a/ppapi/thunk/enter.cc
+++ b/ppapi/thunk/enter.cc
@@ -10,82 +10,136 @@
 #include "base/stringprintf.h"
 #include "ppapi/c/pp_errors.h"
 #include "ppapi/shared_impl/ppapi_globals.h"
+#include "ppapi/shared_impl/tracked_callback.h"
 #include "ppapi/thunk/ppb_instance_api.h"
 #include "ppapi/thunk/resource_creation_api.h"
 
 namespace ppapi {
+namespace {
+
+bool IsMainThread() {
+  return
+      PpapiGlobals::Get()->GetMainThreadMessageLoop()->BelongsToCurrentThread();
+}
+
+}  // namespace
+
 namespace thunk {
 
 namespace subtle {
 
-bool CallbackIsRequired(const PP_CompletionCallback& callback) {
-  return callback.func != NULL &&
-         (callback.flags & PP_COMPLETIONCALLBACK_FLAG_OPTIONAL) == 0;
+EnterBase::EnterBase()
+    : resource_(NULL),
+      retval_(PP_OK) {
+  // TODO(dmichael) validate that threads have an associated message loop.
 }
 
-EnterBase::EnterBase()
-    : callback_(PP_BlockUntilComplete()),
+EnterBase::EnterBase(PP_Resource resource)
+    : resource_(GetResource(resource)),
       retval_(PP_OK) {
-  // TODO(brettw) validate threads.
+  // TODO(dmichael) validate that threads have an associated message loop.
 }
 
-EnterBase::EnterBase(const PP_CompletionCallback& callback)
-    : callback_(CallbackIsRequired(callback) ? callback
-                                             : PP_BlockUntilComplete()),
+EnterBase::EnterBase(PP_Resource resource,
+                     const PP_CompletionCallback& callback)
+    : resource_(GetResource(resource)),
       retval_(PP_OK) {
-  // TODO(brettw) validate threads.
+  callback_ = new TrackedCallback(resource_, callback);
+
+  // TODO(dmichael) validate that threads have an associated message loop.
 }
 
 EnterBase::~EnterBase() {
-  if (callback_.func) {
-    // All async completions should have cleared the callback in SetResult().
-    DCHECK(retval_ != PP_OK_COMPLETIONPENDING && retval_ != PP_OK);
-    MessageLoop::current()->PostTask(FROM_HERE, RunWhileLocked(base::Bind(
-        callback_.func, callback_.user_data, retval_)));
-  }
+  // callback_ is cleared any time it is run, scheduled to be run, or once we
+  // know it will be completed asynchronously. So by this point it should be
+  // NULL.
+  DCHECK(!callback_);
 }
 
 int32_t EnterBase::SetResult(int32_t result) {
-  if (!callback_.func || result == PP_OK_COMPLETIONPENDING) {
-    // Easy case, we don't need to issue the callback (either none is
-    // required, or the implementation will asynchronously issue it
-    // for us), just store the result.
-    callback_ = PP_BlockUntilComplete();
+  if (!callback_) {
+    // It doesn't make sense to call SetResult if there is no callback.

[brettw, 2012/05/20 17:46:46]

I don't see why you "shouldn't" call this when there's no callback. Maybe just
remove this assertion?

[dmichael (off chromium), 2012/05/22 18:08:39]

I didn't really want to have to code for that case and almost just had:
DCHECK(callback_);
But I thought I should have somewhat reasonable behavior in that case. IMHO it's
not clear what it means to call SetResult with no callback; what I have here is
probably appropriate, but maybe a developer trying to do this would have a
different intent. So I like the assertion.

+    NOTREACHED();
     retval_ = result;
-    return retval_;
+    return result;
   }
-
-  // This is a required callback, asynchronously issue it.
-  // TODO(brettw) make this work on different threads, etc.
-  MessageLoop::current()->PostTask(FROM_HERE, RunWhileLocked(base::Bind(
-      callback_.func, callback_.user_data, result)));
-
-  // Now that the callback will be issued in the future, we should return
-  // "pending" to the caller, and not issue the callback again.
-  callback_ = PP_BlockUntilComplete();
-  retval_ = PP_OK_COMPLETIONPENDING;
+  if (result == PP_OK_COMPLETIONPENDING) {
+    retval_ = result;
+    if (callback_->is_blocking()) {
+      DCHECK(!IsMainThread());  // We should have returned an error before this.
+      retval_ = callback_->BlockUntilComplete();
+    } else {
+      // The callback is not blocking and the operation will complete
+      // asynchronously, so there's nothing to do.
+      retval_ = result;
+    }
+  } else {
+    // The function completed synchronously.
+    if (callback_->is_required()) {
+      // This is a required callback, so we must issue it asynchronously.
+      // TODO(dmichael) make this work so that a call from a background thread
+      // goes back to that thread.
+      callback_->PostRun(result);
+      retval_ = PP_OK_COMPLETIONPENDING;
+    } else {
+      // The callback is blocking or optional, so all we need to do is mark
+      // the callback as completed so that it won't be issued later.
+      callback_->MarkAsCompleted();
+      retval_ = result;
+    }
+  }
+  callback_ = NULL;
   return retval_;
 }
 
-Resource* EnterBase::GetResource(PP_Resource resource) const {
+// static
+Resource* EnterBase::GetResource(PP_Resource resource) {
   return PpapiGlobals::Get()->GetResourceTracker()->GetResource(resource);
 }
 
+void EnterBase::SetStateForCallbackError(bool report_error) {
+  if (!CallbackIsValid()) {
+    callback_->MarkAsCompleted();
+    callback_ = NULL;
+    retval_ = PP_ERROR_BLOCKS_MAIN_THREAD;
+    if (report_error) {
+      std::string message(
+          "Blocking callbacks are not allowed on the main thread.");
+      PpapiGlobals::Get()->BroadcastLogWithSource(0, PP_LOGLEVEL_ERROR,
+                                                  std::string(), message);
+    }
+  }
+}
+
+bool EnterBase::CallbackIsValid() const {
+  // A callback is only considered invalid if it is blocking and we're on the
+  // main thread.
+  return !callback_ || !callback_->is_blocking() || !IsMainThread();
+}
+
+void EnterBase::ClearCallback() {
+  callback_ = NULL;
+}
+
 void EnterBase::SetStateForResourceError(PP_Resource pp_resource,
                                          Resource* resource_base,
                                          void* object,
                                          bool report_error) {
+  SetStateForCallbackError(report_error);

[brettw, 2012/05/20 17:46:46]

This function call should return early on error. If the resource is invalid then
it will overwrite the error. That's probably OK in practice, but seems weird.

[dmichael (off chromium), 2012/05/22 18:08:39]

My intent was to have both log messages come out, but return
PP_ERROR_BADRESOURCE. I'll update the documentation to reflect that.

[brettw, 2012/06/01 21:11:32]

Did you update the documentation? I don't see anything.

+
   if (object)
     return;  // Everything worked.
 
-  if (callback_.func) {
-    // Required callback, issue the async completion.
-    MessageLoop::current()->PostTask(FROM_HERE, RunWhileLocked(base::Bind(
-        callback_.func, callback_.user_data,
-        static_cast<int32_t>(PP_ERROR_BADRESOURCE))));
-    callback_ = PP_BlockUntilComplete();
+  if (callback_ && callback_->is_required()) {
+    // TODO(dmichael) make this work so that a call from a background thread
+    // goes back to that thread.
+    callback_->PostRun(static_cast<int32_t>(PP_ERROR_BADRESOURCE));
+    callback_ = NULL;
     retval_ = PP_OK_COMPLETIONPENDING;
   } else {
+    if (callback_)
+      callback_->MarkAsCompleted();
+    callback_ = NULL;
     retval_ = PP_ERROR_BADRESOURCE;
   }
 
@@ -111,17 +165,19 @@ void EnterBase::SetStateForResourceError(PP_Resource pp_resource,
 void EnterBase::SetStateForFunctionError(PP_Instance pp_instance,
                                          void* object,
                                          bool report_error) {
+  SetStateForCallbackError(report_error);
+
   if (object)
     return;  // Everything worked.
 
-  if (callback_.func) {
-    // Required callback, issue the async completion.
-    MessageLoop::current()->PostTask(FROM_HERE, RunWhileLocked(base::Bind(
-        callback_.func, callback_.user_data,
-        static_cast<int32_t>(PP_ERROR_BADARGUMENT))));
-    callback_ = PP_BlockUntilComplete();
+  if (callback_ && callback_->is_required()) {
+    callback_->PostRun(static_cast<int32_t>(PP_ERROR_BADARGUMENT));
+    callback_ = NULL;
     retval_ = PP_OK_COMPLETIONPENDING;
   } else {
+    if (callback_)
+      callback_->MarkAsCompleted();
+    callback_ = NULL;
     retval_ = PP_ERROR_BADARGUMENT;
   }
 
@@ -147,7 +203,10 @@ EnterInstance::EnterInstance(PP_Instance instance)
 
 EnterInstance::EnterInstance(PP_Instance instance,
                              const PP_CompletionCallback& callback)
-    : EnterBase(callback),
+    : EnterBase(0 /* resource */, callback),
+    // TODO(dmichael): This means that the callback_ we get is not associated
+    //                 even with the instance, but we should handle that for
+    //                 MouseLock (maybe others?).
       functions_(PpapiGlobals::Get()->GetInstanceAPI(instance)) {
   SetStateForFunctionError(instance, functions_, true);
 }