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diff --git a/meson/mesonbuild/compilers/mixins/emscripten.py b/meson/mesonbuild/compilers/mixins/emscripten.py
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+++ b/meson/mesonbuild/compilers/mixins/emscripten.py
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+# Copyright 2019 The meson development team
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Provides a mixin for shared code between C and C++ Emscripten compilers."""
+
+import os.path
+import typing as T
+
+from ... import coredata
+from ...mesonlib import OptionKey
+
+if T.TYPE_CHECKING:
+    from ...environment import Environment
+    from ...compilers.compilers import Compiler
+else:
+    # This is a bit clever, for mypy we pretend that these mixins descend from
+    # Compiler, so we get all of the methods and attributes defined for us, but
+    # for runtime we make them descend from object (which all classes normally
+    # do). This gives up DRYer type checking, with no runtime impact
+    Compiler = object
+
+
+class EmscriptenMixin(Compiler):
+
+    def _get_compile_output(self, dirname: str, mode: str) -> str:
+        # In pre-processor mode, the output is sent to stdout and discarded
+        if mode == 'preprocess':
+            return None
+        # Unlike sane toolchains, emcc infers the kind of output from its name.
+        # This is the only reason why this method is overridden; compiler tests
+        # do not work well with the default exe/obj suffices.
+        if mode == 'link':
+            suffix = 'js'
+        else:
+            suffix = 'o'
+        return os.path.join(dirname, 'output.' + suffix)
+
+    def thread_flags(self, env: 'Environment') -> T.List[str]:
+        return ['-s', 'USE_PTHREADS=1']
+
+    def thread_link_flags(self, env: 'Environment') -> T.List[str]:
+        args = ['-s', 'USE_PTHREADS=1']
+        count: int = env.coredata.options[OptionKey('thread_count', lang=self.language, machine=self.for_machine)].value
+        if count:
+            args.extend(['-s', f'PTHREAD_POOL_SIZE={count}'])
+        return args
+
+    def get_options(self) -> 'coredata.KeyedOptionDictType':
+        opts = super().get_options()
+        key = OptionKey('thread_count', machine=self.for_machine, lang=self.language)
+        opts.update({
+            key: coredata.UserIntegerOption(
+                'Number of threads to use in web assembly, set to 0 to disable',
+                (0, None, 4),  # Default was picked at random
+            ),
+        })
+
+        return opts