BaseTools: Cap thread count to avoid file descriptor exhaustion

When the number of build threads multiplied by per-thread file
descriptor usage exceeds the system's open file descriptor limit,
some threads may fail to acquire necessary resources (e.g., pipes
or semaphores), leading to deadlocks or hangs during parallel builds.

To prevent this situation, calculate the safety upper limit of
concurrency by dividing the system's maximum file descriptor limit by
4 (multi-processing pipelines use three file descriptors, and POSIX
named semaphores use one file descriptor). The actual thread count is
then clamped to this safe value.

This ensures stable parallel builds even under constrained resource
limits.

Signed-off-by: Ayden Meng <[email protected]>

Author: Ayden Meng

BaseTools/Source/Python/build/build.py

@@ -25,6 +25,7 @@
 import traceback
 import multiprocessing
 import errno
+import resource
 from threading import Thread,Event,BoundedSemaphore
 import threading
 from linecache import getlines
@@ -838,13 +839,15 @@ def StartAutoGen(self,mqueue, DataPipe,SkipAutoGen,PcdMaList,cqueue):
         try:
             if SkipAutoGen:
                 return True,0
+            soft, hard = resource.getrlimit(resource.RLIMIT_NOFILE)
             feedback_q = mp.Queue()
             error_event = mp.Event()
             FfsCmd = DataPipe.Get("FfsCommand")
             if FfsCmd is None:
                 FfsCmd = {}
             GlobalData.FfsCmd = FfsCmd
-            auto_workers = [AutoGenWorkerInProcess(mqueue,DataPipe.dump_file,feedback_q,GlobalData.file_lock,cqueue,self.log_q,error_event) for _ in range(self.ThreadNumber)]
+
+            auto_workers = [AutoGenWorkerInProcess(mqueue,DataPipe.dump_file,feedback_q,GlobalData.file_lock,cqueue,self.log_q,error_event) for _ in range(min(self.ThreadNumber, soft // 4))]
             self.AutoGenMgr = AutoGenManager(auto_workers,feedback_q,error_event)
             self.AutoGenMgr.start()
             for w in auto_workers: