Synchronization problem with multiple writers

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C++

Linux

IPC

Boost

Hello,

I have multiple writers in a form of separate processes which will get a signal at the same time to start writing on a managed shared memory segment, each writer will create its own unique managed object. On the other hand I have one reader only as a separate process. Which can access this managed shared memory and has knowledge about the created managed objects by each writer. Due to this design I have the following two problems:

1. I want to find a way to let the last writer to signal the reader to start reading.
2. Maybe during the first phase of writing, another signal may arrive, and the writers have to write again on the shared memory. But they shouldn't do that, until the reader has finished reading the first phase.

So how can I solve these two problems using Boost library?
What Synchronization mechanism do I need? And how to do that?

Thanks a lot.