Fix futex locking for linux

diff --git a/threadskv9c.c b/threadskv9c.c
index c13577a7e632bd39f16c1c0e427d798196a0af55..974beeb5c93ad244ae575cd3fb89886556ca9bb1 100644 (file)
--- a/threadskv9c.c
+++ b/threadskv9c.c
@@ -109,6 +109,28 @@ typedef enum{
        BtLockAtomic = 32
 } BtLock;
 
+//     lite weight mutex
+
+typedef struct {
+  union {
+       struct {
+         uint xlock:1;         // one writer has exclusive lock
+         uint wrt:31;          // count of other writers waiting
+       } bits[1];
+       uint value[1];
+  };
+} BtMutexLatch;
+
+#define XCL 1
+#define WRT 2
+
+//     mode & definition for lite latch implementation
+
+enum {
+       QueRd = 1,              // reader queue
+       QueWr = 2               // writer queue
+} RWQueue;
+
 //     definition for phase-fair reader/writer lock implementation
 
 typedef struct {
@@ -123,8 +145,7 @@ typedef struct {
 //     write only lock
 
 typedef struct {
-       volatile ushort ticket[1];
-       volatile ushort serving[1];
+       BtMutexLatch xcl[1];
        ushort tid;
        ushort dup;
 } WOLock;
@@ -134,24 +155,6 @@ typedef struct {
 #define MASK 0x3
 #define RINC 0x4
 
-//     lite weight mutex
-
-// exclusive is set for write access
-
-typedef struct {
-       volatile unsigned char exclusive[1];
-       unsigned char filler;
-} BtMutexLatch;
-
-#define XCL 1
-
-//     mode & definition for lite latch implementation
-
-enum {
-       QueRd = 1,              // reader queue
-       QueWr = 2               // writer queue
-} RWQueue;
-
 //  hash table entries
 
 typedef struct {
@@ -466,29 +469,75 @@ uid bt_newdup (BtDb *bt)
 #endif
 }
 
+//     lite weight spin lock Latch Manager
+
+int sys_futex(void *addr1, int op, int val1, struct timespec *timeout, void *addr2, int val3)
+{
+       return syscall(SYS_futex, addr1, op, val1, timeout, addr2, val3);
+}
+
+void bt_mutexlock(BtMutexLatch *latch)
+{
+BtMutexLatch prev[1];
+uint slept = 0;
+
+  while( 1 ) {
+       *prev->value = __sync_fetch_and_or(latch->value, XCL);
+
+       if( !prev->bits->xlock ) {                      // did we set XCL bit?
+           if( slept )
+                 __sync_fetch_and_sub(latch->value, WRT);
+               return;
+       }
+
+       if( !slept ) {
+               prev->bits->wrt++;
+               __sync_fetch_and_add(latch->value, WRT);
+       }
+
+       sys_futex (latch->value, FUTEX_WAIT_BITSET, *prev->value, NULL, NULL, QueWr);
+       slept = 1;
+  }
+}
+
+//     try to obtain write lock
+
+//     return 1 if obtained,
+//             0 otherwise
+
+int bt_mutextry(BtMutexLatch *latch)
+{
+BtMutexLatch prev[1];
+
+       *prev->value = __sync_fetch_and_or(latch->value, XCL);
+
+       //      take write access if exclusive bit is clear
+
+       return !prev->bits->xlock;
+}
+
+//     clear write mode
+
+void bt_releasemutex(BtMutexLatch *latch)
+{
+BtMutexLatch prev[1];
+
+       *prev->value = __sync_fetch_and_and(latch->value, ~XCL);
+
+       if( prev->bits->wrt )
+         sys_futex( latch->value, FUTEX_WAKE_BITSET, 1, NULL, NULL, QueWr );
+}
+
 //     Write-Only Queue Lock
 
 void WriteOLock (WOLock *lock, ushort tid)
 {
-ushort tix;
-
        if( lock->tid == tid ) {
                lock->dup++;
                return;
        }
-#ifdef unix
-       tix = __sync_fetch_and_add (lock->ticket, 1);
-#else
-       tix = _InterlockedExchangeAdd16 (lock->ticket, 1);
-#endif
-       // wait for our ticket to come up
 
-       while( tix != lock->serving[0] )
-#ifdef unix
-               sched_yield();
-#else
-               SwitchToThread ();
-#endif
+       bt_mutexlock(lock->xcl);
        lock->tid = tid;
 }
 
@@ -500,7 +549,7 @@ void WriteORelease (WOLock *lock)
        }
 
        lock->tid = 0;
-       lock->serving[0]++;
+       bt_releasemutex(lock->xcl);
 }
 
 //     Phase-Fair reader/writer lock implementation
@@ -624,60 +673,6 @@ void ReadRelease (RWLock *lock)
 #endif
 }
 
-//     lite weight spin lock Latch Manager
-
-int sys_futex(void *addr1, int op, int val1, struct timespec *timeout, void *addr2, int val3)
-{
-       return syscall(SYS_futex, addr1, op, val1, timeout, addr2, val3);
-}
-
-void bt_mutexlock(BtMutexLatch *latch)
-{
-unsigned char prev;
-
-  do {
-#ifdef  unix
-       prev = __sync_fetch_and_or(latch->exclusive, XCL);
-#else
-       prev = _InterlockedOr8(latch->exclusive, XCL);
-#endif
-       if( !(prev & XCL) )
-               return;
-#ifdef  unix
-  } while( sched_yield(), 1 );
-#else
-  } while( SwitchToThread(), 1 );
-#endif
-}
-
-//     try to obtain write lock
-
-//     return 1 if obtained,
-//             0 otherwise
-
-int bt_mutextry(BtMutexLatch *latch)
-{
-uint prev;
-
-#ifdef  unix
-       prev = __sync_fetch_and_or(latch->exclusive, XCL);
-#else
-       prev = _InterlockedOr8(latch->exclusive, XCL);
-#endif
-       //      take write access if exclusive bit is clear
-
-       return !(prev & XCL);
-}
-
-//     clear write mode
-
-void bt_releasemutex(BtMutexLatch *latch)
-{
-       *latch->exclusive = 0;
-}
-
-//     recovery manager -- flush dirty pages
-
 void bt_flushlsn (BtDb *bt)
 {
 uint cnt3 = 0, cnt2 = 0, cnt = 0;
@@ -3567,13 +3562,13 @@ uint entry = 0;
                if( *latch->access->rin & MASK )
                        fprintf(stderr, "latchset %d accesslocked for page %d\n", entry, latch->page_no);
 
-               if( *latch->parent->ticket != *latch->parent->serving )
+               if( *latch->parent->xcl->value )
                        fprintf(stderr, "latchset %d parentlocked for page %d\n", entry, latch->page_no);
 
-               if( *latch->atomic->ticket != *latch->atomic->serving )
+               if( *latch->atomic->xcl->value )
                        fprintf(stderr, "latchset %d atomiclocked for page %d\n", entry, latch->page_no);
 
-               if( *latch->modify->exclusive )
+               if( *latch->modify->value )
                        fprintf(stderr, "latchset %d modifylocked for page %d\n", entry, latch->page_no);
 
                if( latch->pin & ~CLOCK_bit )