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shared_ostream

Language: 한국어 | English  |  <- Example gallery

The smallest example. Two modules attached to the same Runtime alternate writes into one std::ostringstream with no locks. It demonstrates one of uniflow's essential properties: every step body on the same Runtime runs on one pump thread. Whether two modules or ten, a resource can be shared with no mutex and no race.

It is a finite console program: it runs the two writers, prints the interleaved-yet-ordered output, verifies it, then exits. There is no dashboard and no Enter-to-quit; the verification step confirms the result.

Feature focus

Lock-free shared state on one pump thread. Two Flow_Writer modules touch the same std::ostringstream and the same turn flag with no mutex anywhere. Because the Runtime drives every step on a single pump thread, the shared sink stays consistent and the output order is exactly preserved.

What it shows

  • Two Flow_Writer instances ("Hello", "World") running on the same pump thread
  • Order enforced by a shared turn flag (SharedState::Turn()) - no lock
  • Output verification: "Hello World." must appear exactly 10 times
  • A SilentObserver so the framework's default trace does not pollute stdout

File map

File Role
main.cpp entry point + verification (counts "Hello World.")
app.h one Runtime, two Flow_Writer, two-phase init, SilentObserver
uf_writer.h / uf_writer.cpp the Flow_Writer module and its Task_Write steps (the lock-free core)
shared_state.h / shared_state.cpp the shared ostringstream and turn flag every writer touches

Build / run

A console example, platform-independent.

Linux / macOS (g++):

g++ -std=c++17 -O2 -I../.. *.cpp -o shared_ostream -pthread
./shared_ostream

Windows (MSVC, from inside this directory after vcvars64.bat):

cl /std:c++17 /EHsc /W4 /nologo /I..\.. *.cpp /Fe:shared_ostream.exe
.\shared_ostream.exe

Output:

=== shared_ostream: two writers, one log, no locks ===

--- output ---
Hello World. Hello World. Hello World. Hello World. Hello World. Hello World. Hello World. Hello World. Hello World. Hello World.
--- end ---

expected "Hello World." occurrences = 10, got = 10
PASS: shared log is race-free, order preserved

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