compilers/mixins/emscripten: Implement thread support

Emscripten has pthread support (as well as C++ threads), but we don't
currently implement them. This fixes that by adding the necessary code.
The one thing I'm not sure about is setting the pool size. The docs
suggest that you really want to do this to ensure that your code works
correctly, but the number should really be configurable, not sure how to
set that.

Fixes #6684

3 files changed, 28 insertions, 2 deletions

diff --git a/mesonbuild/compilers/c.py b/mesonbuild/compilers/c.py
index e27eb90..f3ed9e8 100644
--- a/mesonbuild/compilers/c.py
+++ b/mesonbuild/compilers/c.py
@@ -133,7 +133,7 @@ class AppleClangCCompiler(ClangCCompiler):
     _C18_VERSION = '>=11.0.0'
 
 
-class EmscriptenCCompiler(BasicLinkerIsCompilerMixin, LinkerEnvVarsMixin, EmscriptenMixin, ClangCCompiler):
+class EmscriptenCCompiler(EmscriptenMixin, BasicLinkerIsCompilerMixin, LinkerEnvVarsMixin, ClangCCompiler):
     def __init__(self, exelist, version, for_machine: MachineChoice,
                  is_cross: bool, info: 'MachineInfo', exe_wrapper=None, **kwargs):
         if not is_cross:
diff --git a/mesonbuild/compilers/cpp.py b/mesonbuild/compilers/cpp.py
index f6f4cfc..2a244e9 100644
--- a/mesonbuild/compilers/cpp.py
+++ b/mesonbuild/compilers/cpp.py
@@ -201,7 +201,7 @@ class AppleClangCPPCompiler(ClangCPPCompiler):
     pass
 
 
-class EmscriptenCPPCompiler(BasicLinkerIsCompilerMixin, LinkerEnvVarsMixin, EmscriptenMixin, ClangCPPCompiler):
+class EmscriptenCPPCompiler(EmscriptenMixin, BasicLinkerIsCompilerMixin, LinkerEnvVarsMixin, ClangCPPCompiler):
     def __init__(self, exelist, version, for_machine: MachineChoice,
                  is_cross: bool, info: 'MachineInfo', exe_wrapper=None, **kwargs):
         if not is_cross:
diff --git a/mesonbuild/compilers/mixins/emscripten.py b/mesonbuild/compilers/mixins/emscripten.py
index 36a757a..ee86ce4 100644
--- a/mesonbuild/compilers/mixins/emscripten.py
+++ b/mesonbuild/compilers/mixins/emscripten.py
@@ -17,8 +17,13 @@
 import os.path
 import typing as T
 
+from ... import coredata
 from ...mesonlib import MesonException
 
+if T.TYPE_CHECKING:
+    from ..environment import Environment
+
+
 class EmscriptenMixin:
 
     def get_option_link_args(self, options):
@@ -45,3 +50,24 @@ class EmscriptenMixin:
         else:
             suffix = 'wasm'
         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 = env.coredata.compiler_options[self.for_machine]['{}_thread_count'.format(self.language)].value  # type: int
+        if count:
+            args.extend(['-s', 'PTHREAD_POOL_SIZE={}'.format(count)])
+        return args
+
+    def get_options(self):
+        opts = super().get_options()
+        opts.update({
+            '{}_thread_count'.format(self.language): 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