Blocking vs. Non-Blocking Primitives

send

receive

blocking

non-blocking

Returns control as soon as

message queued or copied.

Signals willingness to

receive message.

Buffer is ready.

Returns control to user

only after message has

been sent, or until

acknowledgment has

been received.

Returns only after message

has been received.

• Need buffering:
  • still blocking
  • deadlocks!

• Tricky to program.

• Reduces concurrency.

problems

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