test(symdb): add fork behaviour test (#15079)

## Description

We add a test to the Symbol DB test to ensure that we have the expected
fork behaviour. By design, we want only the main process and the first
fork child to emit Symbol DB payloads.

Author: P403n1x87

ddtrace/internal/symbol_db/remoteconfig.py

@@ -19,7 +19,7 @@
 log = get_logger(__name__)
 
 
-def _rc_callback(data: t.List[Payload], test_tracer=None):
+def _rc_callback(data: t.Sequence[Payload]):
     if get_ancestor_runtime_id() is not None and has_forked():
         log.debug("[PID %d] SymDB: Disabling Symbol DB in forked process", os.getpid())
         # We assume that forking is being used for spawning child worker

tests/internal/symbol_db/test_symbols.py

@@ -286,3 +286,37 @@ def get_scope(contexts, name):
     scope = get_scope(contexts, "tests.submod.stuff")
     assert scope["scope_type"] == ScopeType.MODULE
     assert scope["name"] == "tests.submod.stuff"
+
+
+@pytest.mark.subprocess(ddtrace_run=True, err=None)
+def test_symbols_fork_uploads():
+    """
+    Test that we disable Symbol DB on processes that are not the main one nor
+    the first fork child.
+    """
+    import os
+
+    from ddtrace.internal import forksafe
+    from ddtrace.internal.remoteconfig import ConfigMetadata
+    from ddtrace.internal.remoteconfig import Payload
+    from ddtrace.internal.runtime import get_ancestor_runtime_id
+    from ddtrace.internal.symbol_db.remoteconfig import _rc_callback
+    from ddtrace.internal.symbol_db.symbols import SymbolDatabaseUploader
+
+    SymbolDatabaseUploader.install()
+
+    pids = []
+    rc_data = [Payload(ConfigMetadata("test", "symdb", "hash", 0, 0), "test", None)]
+
+    for _ in range(10):
+        if not (pid := os.fork()):
+            _rc_callback(rc_data)
+            assert SymbolDatabaseUploader.is_installed() != (
+                get_ancestor_runtime_id() is not None and forksafe.has_forked()
+            )
+            os._exit(0)
+
+        pids.append(pid)
+
+    for pid in pids:
+        os.waitpid(pid, 0)