waf/backend: limit parallel link tasks with MAX_LINK_TASKS.

Linking is memory-intensive, so on machines with many CPUs, running too
many link tasks in parallel can exhaust memory and disk I/O. Use waf's
TaskSemaphore to cap link task parallelism to 8 by default, configurable
via the MAX_LINK_TASKS environment variable.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Change-Id: I401dbbc18e2b76e7796aec77b4b7f6fe495e0131
Priv-Id: ae987beb7863683fd5cd5c7acbcc4152fe84d027

Author: LpZ-squall

README.adoc

@@ -266,6 +266,14 @@ The following environment variables can be used at the configuration phase:
     If the variable is not set, only the release and dev dependencies are
     installed.
 
+The following environment variables can be used at the build phase:
+
+`MAX_LINK_TASKS` (integer)::
+    Limit the number of link tasks that can run in parallel. Linking is
+    memory-intensive, so on machines with many CPUs, running too many link
+    tasks in parallel can exhaust memory and disk I/O.
+    Defaults to 8 if not set.
+
 ==== Compiling with gcc
 
 An important part of the lib-common uses the

build/waftools/backend.py

@@ -49,7 +49,7 @@
 from waflib.Configure import ConfigurationContext
 from waflib.Node import Node
 from waflib.Options import OptionsContext
-from waflib.Task import Task
+from waflib.Task import Task, TaskSemaphore
 from waflib.Tools import (
     c as c_tool,
     c_preproc,
@@ -2055,6 +2055,13 @@ def build(ctx: BuildContext) -> None:
     ctx.env.GEN_FILES = set()
     ctx.env.CHECKED_FILES = set()
 
+    # Limit the number of parallel link tasks. Linking is memory-intensive,
+    # so on machines with many CPUs, running too many link tasks in parallel
+    # can exhaust memory and disk I/O.
+    max_link_tasks = int(os.environ.get('MAX_LINK_TASKS', '8'))
+    Logs.info(f'Waf: Limiting parallel link tasks to {max_link_tasks}')
+    ccroot.link_task.semaphore = TaskSemaphore(max_link_tasks)
+
     register_get_cwd()
 
     # iopc options