fix(tracer): fix file queue on read only file sytems (#10004)

- ensure file queue will be properly disabled on read only file systems
- ensure the tmp file will not grow beyond the max file size of 8192
bytes (previously one more write was possible)
- small improvements

Multiple service name reports will be disabled on file systems where
python can create a temporary directory or file.

## Checklist
- [x] PR author has checked that all the criteria below are met
- The PR description includes an overview of the change
- The PR description articulates the motivation for the change
- The change includes tests OR the PR description describes a testing
strategy
- The PR description notes risks associated with the change, if any
- Newly-added code is easy to change
- The change follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
- [ ] Reviewer has checked that all the criteria below are met 
- Title is accurate
- All changes are related to the pull request's stated goal
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
- Newly-added code is easy to change
- Release note makes sense to a user of the library
- If necessary, author has acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment
- Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

ddtrace/internal/_file_queue.py

@@ -5,6 +5,10 @@
 import typing
 
 from ddtrace.internal._unpatched import unpatched_open
+from ddtrace.internal.logger import get_logger
+
+
+log = get_logger(__name__)
 
 
 MAX_FILE_SIZE = 8192
@@ -56,23 +60,34 @@ class File_Queue:
     """A simple file-based queue implementation for multiprocess communication."""
 
     def __init__(self) -> None:
-        self.directory = tempfile.gettempdir()
-        self.filename = os.path.join(self.directory, secrets.token_hex(8))
+        try:
+            self._directory: typing.Optional[str] = tempfile.gettempdir()
+            self.filename: typing.Optional[str] = os.path.join(self._directory, secrets.token_hex(8))
+        except Exception as e:
+            info = f"Failed to create a temporary file for the file queue. {e}"
+            log.debug(info)
+            self._directory = None
+            self.filename = None
 
     def put(self, data: str) -> None:
         """Push a string to the queue."""
+        if self.filename is None:
+            return
         try:
             with open_file(self.filename, "ab") as f:
                 lock(f)
                 f.seek(0, os.SEEK_END)
-                if f.tell() < MAX_FILE_SIZE:
-                    f.write((data + "\x00").encode())
+                dt = (data + "\x00").encode()
+                if f.tell() + len(dt) <= MAX_FILE_SIZE:
+                    f.write(dt)
                 unlock(f)
         except Exception:  # nosec
             pass
 
     def get_all(self) -> typing.Set[str]:
         """Pop all unique strings from the queue."""
+        if self.filename is None:
+            return set()
         try:
             with open_file(self.filename, "r+b") as f:
                 lock(f)
@@ -82,7 +97,9 @@ def get_all(self) -> typing.Set[str]:
                 f.truncate()
                 unlock(f)
             if data:
-                return set(data.split("\x00")[:-1])
+                res = data.split("\x00")
+                res.pop()
+                return set(res)
         except Exception:  # nosec
             pass
         return set()

releasenotes/notes/fix_file_queue_on_readonly_file_systems-02bb11edeecf52e9.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    tracer: This fix resolves an issue where the tracer was not starting properly on a read-only file system.