Grab a file lock on the build dir during modifications.

3 files changed, 53 insertions, 1 deletions

diff --git a/mesonbuild/mesonlib.py b/mesonbuild/mesonlib.py
index 247b4f9..a076e3e 100644
--- a/mesonbuild/mesonlib.py
+++ b/mesonbuild/mesonlib.py
@@ -21,6 +21,21 @@ import platform, subprocess, operator, os, shutil, re
 import collections
 from mesonbuild import mlog
 
+have_fcntl = False
+have_msvcrt = False
+
+try:
+    import fcntl
+    have_fcntl = True
+except Exception:
+    pass
+
+try:
+    import msvcrt
+    have_msvcrt = True
+except Exception:
+    pass
+
 from glob import glob
 
 def detect_meson_py_location():
@@ -978,3 +993,26 @@ class OrderedSet(collections.MutableSet):
 
     def difference(self, set_):
         return type(self)(e for e in self if e not in set_)
+
+class BuildDirLock:
+
+    def __init__(self, builddir):
+        self.lockfilename = os.path.join(builddir, 'meson-private/meson.lock')
+
+    def __enter__(self):
+        self.lockfile = open(self.lockfilename, 'w')
+        try:
+            if have_fcntl:
+                fcntl.flock(self.lockfile, fcntl.LOCK_EX | fcntl.LOCK_NB)
+            elif have_msvcrt:
+                msvcrt.locking(self.lockfile.fileno(), msvcrt.LK_NBLCK, 1)
+        except (BlockingIOError, PermissionError):
+            self.lockfile.close()
+            raise MesonException('Some other Meson process is already using this build directory. Exiting.')
+
+    def __exit__(self, *args):
+        if have_fcntl:
+            fcntl.flock(self.lockfile, fcntl.LOCK_UN)
+        elif have_msvcrt:
+            msvcrt.locking(self.lockfile.fileno(), msvcrt.LK_UNLCK, 1)
+        self.lockfile.close()
diff --git a/mesonbuild/mesonmain.py b/mesonbuild/mesonmain.py
index 9c4498c..651224e 100644
--- a/mesonbuild/mesonmain.py
+++ b/mesonbuild/mesonmain.py
@@ -147,7 +147,8 @@ class MesonApp:
     def generate(self):
         env = environment.Environment(self.source_dir, self.build_dir, self.meson_script_launcher, self.options, self.original_cmd_line_args)
         mlog.initialize(env.get_log_dir())
-        self._generate(env)
+        with mesonlib.BuildDirLock(self.build_dir):
+            self._generate(env)
 
     def _generate(self, env):
         mlog.debug('Build started at', datetime.datetime.now().isoformat())
diff --git a/run_unittests.py b/run_unittests.py
index 3ea0412..b6367c1 100755
--- a/run_unittests.py
+++ b/run_unittests.py
@@ -37,6 +37,7 @@ from mesonbuild.interpreter import ObjectHolder
 from mesonbuild.mesonlib import (
     is_windows, is_osx, is_cygwin, is_dragonflybsd,
     windows_proof_rmtree, python_command, meson_command, version_compare,
+    BuildDirLock
 )
 from mesonbuild.environment import Environment, detect_ninja
 from mesonbuild.mesonlib import MesonException, EnvironmentException
@@ -1882,6 +1883,18 @@ int main(int argc, char **argv) {
         self.init(testdir, extra_args=['--layout=flat'])
         self.build()
 
+    def test_flock(self):
+        exception_raised = False
+        with tempfile.TemporaryDirectory() as tdir:
+            os.mkdir(os.path.join(tdir, 'meson-private'))
+            with BuildDirLock(tdir):
+                try:
+                    with BuildDirLock(tdir):
+                        pass
+                except MesonException:
+                    exception_raised = True
+        self.assertTrue(exception_raised, 'Double locking did not raise exception.')
+
 
 class FailureTests(BasePlatformTests):
     '''