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src/hotspot/os/windows/threadCritical_windows.cpp

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18  *
19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20  * or visit www.oracle.com if you need additional information or have any
21  * questions.
22  *
23  */
24 
25 #include "precompiled.hpp"
26 #include "runtime/atomic.hpp"
27 #include "runtime/thread.inline.hpp"
28 #include "runtime/threadCritical.hpp"
29 
30 // OS-includes here
31 # include <windows.h>
32 # include <winbase.h>
33 
34 //
35 // See threadCritical.hpp for details of this class.
36 //
37 
38 static bool initialized = false;
39 static volatile int lock_count = -1;
40 static HANDLE lock_event;
41 static DWORD lock_owner = -1;
42 
43 //
44 // Note that Microsoft's critical region code contains a race
45 // condition, and is not suitable for use. A thread holding the
46 // critical section cannot safely suspend a thread attempting
47 // to enter the critical region. The failure mode is that both
48 // threads are permanently suspended.
49 //
50 // I experiemented with the use of ordinary windows mutex objects
51 // and found them ~30 times slower than the critical region code.
52 //
53 






54 ThreadCritical::ThreadCritical() {
55   DWORD current_thread = GetCurrentThreadId();
56 

57   if (lock_owner != current_thread) {
58     // Grab the lock before doing anything.
59     while (Atomic::cmpxchg(&lock_count, -1, 0) != -1) {
60       if (initialized) {
61         DWORD ret = WaitForSingleObject(lock_event,  INFINITE);
62         assert(ret == WAIT_OBJECT_0, "unexpected return value from WaitForSingleObject");
63       }
64     }
65 
66     // Make sure the event object is allocated.
67     if (!initialized) {
68       // Locking will not work correctly unless this is autoreset.
69       lock_event = CreateEvent(NULL, false, false, NULL);
70       initialized = true;
71     }
72 
73     assert(lock_owner == -1, "Lock acquired illegally.");
74     lock_owner = current_thread;
75   } else {
76     // Atomicity isn't required. Bump the recursion count.
77     lock_count++;
78   }
79 
80   assert(lock_owner == GetCurrentThreadId(), "Lock acquired illegally.");
81 }
82 
83 ThreadCritical::~ThreadCritical() {
84   assert(lock_owner == GetCurrentThreadId(), "unlock attempt by wrong thread");
85   assert(lock_count >= 0, "Attempt to unlock when already unlocked");
86 

87   if (lock_count == 0) {
88     // We're going to unlock
89     lock_owner = -1;
90     lock_count = -1;
91     // No lost wakeups, lock_event stays signaled until reset.
92     DWORD ret = SetEvent(lock_event);
93     assert(ret != 0, "unexpected return value from SetEvent");
94   } else {
95     // Just unwinding a recursive lock;
96     lock_count--;
97   }
98 }

18  *
19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20  * or visit www.oracle.com if you need additional information or have any
21  * questions.
22  *
23  */
24 
25 #include "precompiled.hpp"
26 #include "runtime/atomic.hpp"
27 #include "runtime/thread.inline.hpp"
28 #include "runtime/threadCritical.hpp"
29 
30 // OS-includes here
31 # include <windows.h>
32 # include <winbase.h>
33 
34 //
35 // See threadCritical.hpp for details of this class.
36 //
37 
38 static INIT_ONCE initialized = INIT_ONCE_STATIC_INIT;
39 static int lock_count = 0;
40 static HANDLE lock_event;
41 static DWORD lock_owner = 0;
42 
43 //
44 // Note that Microsoft's critical region code contains a race
45 // condition, and is not suitable for use. A thread holding the
46 // critical section cannot safely suspend a thread attempting
47 // to enter the critical region. The failure mode is that both
48 // threads are permanently suspended.
49 //
50 // I experiemented with the use of ordinary windows mutex objects
51 // and found them ~30 times slower than the critical region code.
52 //
53 
54 static BOOL WINAPI initialize(PINIT_ONCE InitOnce, PVOID Parameter, PVOID *Context) {
55   lock_event = CreateEvent(NULL, false, true, NULL);
56   assert(lock_event != NULL, "unexpected return value from CreateEvent");
57   return true;
58 }
59 
60 ThreadCritical::ThreadCritical() {
61   InitOnceExecuteOnce(&initialized, &initialize, NULL, NULL);
62 
63   DWORD current_thread = GetCurrentThreadId();
64   if (lock_owner != current_thread) {
65     // Grab the lock before doing anything.
66     DWORD ret = WaitForSingleObject(lock_event,  INFINITE);
67     assert(ret == WAIT_OBJECT_0, "unexpected return value from WaitForSingleObject");













68     lock_owner = current_thread;



69   }
70   // Atomicity isn't required. Bump the recursion count.
71   lock_count++;
72 }
73 
74 ThreadCritical::~ThreadCritical() {
75   assert(lock_owner == GetCurrentThreadId(), "unlock attempt by wrong thread");
76   assert(lock_count >= 0, "Attempt to unlock when already unlocked");
77 
78   lock_count--;
79   if (lock_count == 0) {
80     // We're going to unlock
81     lock_owner = 0;

82     // No lost wakeups, lock_event stays signaled until reset.
83     DWORD ret = SetEvent(lock_event);
84     assert(ret != 0, "unexpected return value from SetEvent");



85   }
86 }
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