Mojo: DataPipe: Implement "may discard" for two-phase writes.

mojo/system/data_pipe.cc

Index: mojo/system/data_pipe.cc
diff --git a/mojo/system/data_pipe.cc b/mojo/system/data_pipe.cc
index dac187ecc3fe7d4129716a69aa5a4825a4019fcb..639bb5e7d20b3278060658d69176291c76edbc9b 100644
--- a/mojo/system/data_pipe.cc
+++ b/mojo/system/data_pipe.cc
@@ -79,6 +79,7 @@ void DataPipe::ProducerClose() {
       << "Producer closed with active two-phase write";
   producer_two_phase_max_num_bytes_written_ = 0;
   ProducerCloseImplNoLock();
+  AwakeConsumerWaitersForStateChangeNoLock();
 }
 
 MojoResult DataPipe::ProducerWriteData(const void* elements,
@@ -99,7 +100,11 @@ MojoResult DataPipe::ProducerWriteData(const void* elements,
   if (*num_bytes == 0)
     return MOJO_RESULT_OK;  // Nothing to do.
 
-  return ProducerWriteDataImplNoLock(elements, num_bytes, all_or_none);
+  MojoWaitFlags old_consumer_satisfied_flags = ConsumerSatisfiedFlagsNoLock();
+  MojoResult rv = ProducerWriteDataImplNoLock(elements, num_bytes, all_or_none);
+  if (ConsumerSatisfiedFlagsNoLock() != old_consumer_satisfied_flags)
+    AwakeConsumerWaitersForStateChangeNoLock();
+  return rv;
 }
 
 MojoResult DataPipe::ProducerBeginWriteData(void** buffer,
@@ -117,7 +122,10 @@ MojoResult DataPipe::ProducerBeginWriteData(void** buffer,
                                                    all_or_none);
   if (rv != MOJO_RESULT_OK)
     return rv;
-
+  // Note: No need to awake producer waiters, even though we're going from
+  // writable to non-writable (since you can't wait on non-writability).
+  // Similarly, though this may have discarded data (in "may discard" mode),
+  // making it non-readable, there's still no need to awake consumer waiters.
   DCHECK(producer_in_two_phase_write_no_lock());
   return MOJO_RESULT_OK;
 }
@@ -131,9 +139,16 @@ MojoResult DataPipe::ProducerEndWriteData(uint32_t num_bytes_written) {
   // Note: Allow successful completion of the two-phase write even if the
   // consumer has been closed.
 
+  MojoWaitFlags old_consumer_satisfied_flags = ConsumerSatisfiedFlagsNoLock();
   MojoResult rv = ProducerEndWriteDataImplNoLock(num_bytes_written);
   // Two-phase write ended even on failure.
   DCHECK(!producer_in_two_phase_write_no_lock());
+  // If we're now writable, we *became* writable (since we weren't writable
+  // during the two-phase write), so awake producer waiters.
+  if ((ProducerSatisfiedFlagsNoLock() & MOJO_WAIT_FLAG_WRITABLE))
+    AwakeProducerWaitersForStateChangeNoLock();
+  if (ConsumerSatisfiedFlagsNoLock() != old_consumer_satisfied_flags)
+    AwakeConsumerWaitersForStateChangeNoLock();
   return rv;
 }
 
@@ -175,6 +190,7 @@ void DataPipe::ConsumerClose() {
       << "Consumer closed with active two-phase read";
   consumer_two_phase_max_num_bytes_read_ = 0;
   ConsumerCloseImplNoLock();
+  AwakeProducerWaitersForStateChangeNoLock();
 }
 
 MojoResult DataPipe::ConsumerReadData(void* elements,
@@ -192,7 +208,11 @@ MojoResult DataPipe::ConsumerReadData(void* elements,
   if (*num_bytes == 0)
     return MOJO_RESULT_OK;  // Nothing to do.
 
-  return ConsumerReadDataImplNoLock(elements, num_bytes, all_or_none);
+  MojoWaitFlags old_producer_satisfied_flags = ProducerSatisfiedFlagsNoLock();
+  MojoResult rv = ConsumerReadDataImplNoLock(elements, num_bytes, all_or_none);
+  if (ProducerSatisfiedFlagsNoLock() != old_producer_satisfied_flags)
+    AwakeProducerWaitersForStateChangeNoLock();
+  return rv;
 }
 
 MojoResult DataPipe::ConsumerDiscardData(uint32_t* num_bytes,
@@ -209,7 +229,11 @@ MojoResult DataPipe::ConsumerDiscardData(uint32_t* num_bytes,
   if (*num_bytes == 0)
     return MOJO_RESULT_OK;  // Nothing to do.
 
-  return ConsumerDiscardDataImplNoLock(num_bytes, all_or_none);
+  MojoWaitFlags old_producer_satisfied_flags = ProducerSatisfiedFlagsNoLock();
+  MojoResult rv = ConsumerDiscardDataImplNoLock(num_bytes, all_or_none);
+  if (ProducerSatisfiedFlagsNoLock() != old_producer_satisfied_flags)
+    AwakeProducerWaitersForStateChangeNoLock();
+  return rv;
 }
 
 MojoResult DataPipe::ConsumerQueryData(uint32_t* num_bytes) {
@@ -236,7 +260,6 @@ MojoResult DataPipe::ConsumerBeginReadData(const void** buffer,
                                                   all_or_none);
   if (rv != MOJO_RESULT_OK)
     return rv;
-
   DCHECK(consumer_in_two_phase_read_no_lock());
   return MOJO_RESULT_OK;
 }
@@ -248,9 +271,16 @@ MojoResult DataPipe::ConsumerEndReadData(uint32_t num_bytes_read) {
   if (!consumer_in_two_phase_read_no_lock())
     return MOJO_RESULT_FAILED_PRECONDITION;
 
+  MojoWaitFlags old_producer_satisfied_flags = ProducerSatisfiedFlagsNoLock();
   MojoResult rv = ConsumerEndReadDataImplNoLock(num_bytes_read);
   // Two-phase read ended even on failure.
   DCHECK(!consumer_in_two_phase_read_no_lock());
+  // If we're now readable, we *became* readable (since we weren't readable
+  // during the two-phase read), so awake consumer waiters.
+  if ((ConsumerSatisfiedFlagsNoLock() & MOJO_WAIT_FLAG_READABLE))
+    AwakeConsumerWaitersForStateChangeNoLock();
+  if (ProducerSatisfiedFlagsNoLock() != old_producer_satisfied_flags)
+    AwakeProducerWaitersForStateChangeNoLock();
   return rv;
 }