EDK: Add implementation of data pipe consumer read threshold stuff.

mojo/edk/system/data_pipe.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_EDK_SYSTEM_DATA_PIPE_H_
 #define MOJO_EDK_SYSTEM_DATA_PIPE_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 114 matching lines @@
       Channel* channel,
       void* destination,
       size_t* actual_size,
       std::vector<platform::ScopedPlatformHandle>* platform_handles);
   bool ProducerIsBusy() const;
 
   // These are called by the consumer dispatcher to implement its methods of
   // corresponding names.
   void ConsumerCancelAllAwakables();
   void ConsumerClose();
+  MojoResult ConsumerSetOptions(uint32_t read_threshold_num_bytes);
+  void ConsumerGetOptions(uint32_t* read_threshold_num_bytes);
   // This does not validate its arguments, except to check that |*num_bytes| is
   // a multiple of |element_num_bytes_|.
   MojoResult ConsumerReadData(UserPointer<void> elements,
                               UserPointer<uint32_t> num_bytes,
                               bool all_or_none,
                               bool peek);
   MojoResult ConsumerDiscardData(UserPointer<uint32_t> num_bytes,
                                  bool all_or_none);
   MojoResult ConsumerQueryData(UserPointer<uint32_t> num_bytes);
   MojoResult ConsumerBeginReadData(UserPointer<const void*> buffer,
@@ skipping 43 matching lines @@
 
   // Must be called under |mutex_|.
   bool producer_open_no_lock() const MOJO_SHARED_LOCKS_REQUIRED(mutex_) {
     mutex_.AssertHeld();
     return producer_open_;
   }
   bool consumer_open_no_lock() const MOJO_SHARED_LOCKS_REQUIRED(mutex_) {
     mutex_.AssertHeld();
     return consumer_open_;
   }
+  // Note that this returns the "real" read threshold (never zero).
+  size_t consumer_read_threshold_num_bytes_no_lock() const
+      MOJO_SHARED_LOCKS_REQUIRED(mutex_) {
+    mutex_.AssertHeld();
+    return (consumer_read_threshold_num_bytes_ > 0u)
+               ? consumer_read_threshold_num_bytes_
+               : element_num_bytes_;
+  }
   uint32_t producer_two_phase_max_num_bytes_written_no_lock() const
       MOJO_SHARED_LOCKS_REQUIRED(mutex_) {
     mutex_.AssertHeld();
     return producer_two_phase_max_num_bytes_written_;
   }
   uint32_t consumer_two_phase_max_num_bytes_read_no_lock() const
       MOJO_SHARED_LOCKS_REQUIRED(mutex_) {
     mutex_.AssertHeld();
     return consumer_two_phase_max_num_bytes_read_;
   }
@@ skipping 56 matching lines @@
     return !!consumer_awakable_list_;
   }
 
   const uint32_t element_num_bytes_;
   const uint32_t capacity_num_bytes_;
 
   mutable util::Mutex mutex_;
   // *Known* state of producer or consumer.
   bool producer_open_ MOJO_GUARDED_BY(mutex_);
   bool consumer_open_ MOJO_GUARDED_BY(mutex_);
+  // This may be zero (in which case it "means" |element_num_bytes_|).
+  uint32_t consumer_read_threshold_num_bytes_ MOJO_GUARDED_BY(mutex_);
   // Non-null only if the producer or consumer, respectively, is local.
   std::unique_ptr<AwakableList> producer_awakable_list_ MOJO_GUARDED_BY(mutex_);
   std::unique_ptr<AwakableList> consumer_awakable_list_ MOJO_GUARDED_BY(mutex_);
   // These are nonzero if and only if a two-phase write/read is in progress.
   uint32_t producer_two_phase_max_num_bytes_written_ MOJO_GUARDED_BY(mutex_);
   uint32_t consumer_two_phase_max_num_bytes_read_ MOJO_GUARDED_BY(mutex_);
   std::unique_ptr<DataPipeImpl> impl_ MOJO_GUARDED_BY(mutex_);
 
   MOJO_DISALLOW_COPY_AND_ASSIGN(DataPipe);
 };
 
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_EDK_SYSTEM_DATA_PIPE_H_