Issue #7205: Fix a possible deadlock when using a BZ2File object from several threads at once.

Lib/test/test_bz2.py

@@ -7,6 +7,7 @@ from cStringIO import StringIO
 import os
 import subprocess
 import sys
+import threading
 
 bz2 = import_module('bz2')
 from bz2 import BZ2File, BZ2Compressor, BZ2Decompressor
@@ -306,6 +307,23 @@ class BZ2FileTest(BaseTest):
         else:
             self.fail("1/0 didn't raise an exception")
 
+    def testThreading(self):
+        # Using a BZ2File from several threads doesn't deadlock (issue #7205).
+        data = "1" * 2**20
+        nthreads = 10
+        f = bz2.BZ2File(self.filename, 'wb')
+        try:
+            def comp():
+                for i in range(5):
+                    f.write(data)
+            threads = [threading.Thread(target=comp) for i in range(nthreads)]
+            for t in threads:
+                t.start()
+            for t in threads:
+                t.join()
+        finally:
+            f.close()
+
 
 class BZ2CompressorTest(BaseTest):
     def testCompress(self):

Misc/NEWS

@@ -427,6 +427,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #7205: Fix a possible deadlock when using a BZ2File object from
+  several threads at once.
+
 - Issue #7071: byte-compilation in Distutils is now done with respect to
   sys.dont_write_bytecode.
 

Modules/bz2module.c

@@ -78,7 +78,12 @@ typedef fpos_t Py_off_t;
 
 
 #ifdef WITH_THREAD
-#define ACQUIRE_LOCK(obj) PyThread_acquire_lock(obj->lock, 1)
+#define ACQUIRE_LOCK(obj) do { \
+	if (!PyThread_acquire_lock(obj->lock, 0)) { \
+		Py_BEGIN_ALLOW_THREADS \
+		PyThread_acquire_lock(obj->lock, 1); \
+		Py_END_ALLOW_THREADS \
+	} } while(0)
 #define RELEASE_LOCK(obj) PyThread_release_lock(obj->lock)
 #else
 #define ACQUIRE_LOCK(obj)