Introduce timed waits for condition variables.

Provide ConditionVariableTimedSleep(), like ConditionVariableSleep()
but with a timeout argument.

Author: Shawn Debnath
Reviewed-by: Kyotaro Horiguchi, Thomas Munro
Discussion: https://postgr.es/m/eeb06007ccfe46e399df6af18bfcd15a@EX13D05UWC002.ant.amazon.com

diff --git a/src/backend/storage/lmgr/condition_variable.c b/src/backend/storage/lmgr/condition_variable.c
index 58b7b514720dfc7dec055d38abc62a7363f77cc7..bc8607efe457b980c4d125e84dabd92eb978ca95 100644 (file)
--- a/src/backend/storage/lmgr/condition_variable.c
+++ b/src/backend/storage/lmgr/condition_variable.c
@@ -19,6 +19,7 @@
 #include "postgres.h"
 
 #include "miscadmin.h"
+#include "portability/instr_time.h"
 #include "storage/condition_variable.h"
 #include "storage/ipc.h"
 #include "storage/proc.h"
@@ -122,8 +123,24 @@ ConditionVariablePrepareToSleep(ConditionVariable *cv)
 void
 ConditionVariableSleep(ConditionVariable *cv, uint32 wait_event_info)
 {
-   WaitEvent   event;
-   bool        done = false;
+   (void) ConditionVariableTimedSleep(cv, -1 /* no timeout */ ,
+                                      wait_event_info);
+}
+
+/*
+ * Wait for a condition variable to be signaled or a timeout to be reached.
+ *
+ * Returns true when timeout expires, otherwise returns false.
+ *
+ * See ConditionVariableSleep() for general usage.
+ */
+bool
+ConditionVariableTimedSleep(ConditionVariable *cv, long timeout,
+                           uint32 wait_event_info)
+{
+   long        cur_timeout = -1;
+   instr_time  start_time;
+   instr_time  cur_time;
 
    /*
     * If the caller didn't prepare to sleep explicitly, then do so now and
@@ -143,23 +160,37 @@ ConditionVariableSleep(ConditionVariable *cv, uint32 wait_event_info)
    if (cv_sleep_target != cv)
    {
        ConditionVariablePrepareToSleep(cv);
-       return;
+       return false;
    }
 
-   do
+   /*
+    * Record the current time so that we can calculate the remaining timeout
+    * if we are woken up spuriously.
+    */
+   if (timeout >= 0)
    {
-       CHECK_FOR_INTERRUPTS();
+       INSTR_TIME_SET_CURRENT(start_time);
+       Assert(timeout >= 0 && timeout <= INT_MAX);
+       cur_timeout = timeout;
+   }
+
+   while (true)
+   {
+       WaitEvent   event;
+       bool        done = false;
 
        /*
         * Wait for latch to be set.  (If we're awakened for some other
         * reason, the code below will cope anyway.)
         */
-       (void) WaitEventSetWait(cv_wait_event_set, -1, &event, 1,
+       (void) WaitEventSetWait(cv_wait_event_set, cur_timeout, &event, 1,
                                wait_event_info);
 
        /* Reset latch before examining the state of the wait list. */
        ResetLatch(MyLatch);
 
+       CHECK_FOR_INTERRUPTS();
+
        /*
         * If this process has been taken out of the wait list, then we know
         * that it has been signaled by ConditionVariableSignal (or
@@ -182,7 +213,23 @@ ConditionVariableSleep(ConditionVariable *cv, uint32 wait_event_info)
            proclist_push_tail(&cv->wakeup, MyProc->pgprocno, cvWaitLink);
        }
        SpinLockRelease(&cv->mutex);
-   } while (!done);
+
+       /* We were signaled, so return */
+       if (done)
+           return false;
+
+       /* If we're not done, update cur_timeout for next iteration */
+       if (timeout >= 0)
+       {
+           INSTR_TIME_SET_CURRENT(cur_time);
+           INSTR_TIME_SUBTRACT(cur_time, start_time);
+           cur_timeout = timeout - (long) INSTR_TIME_GET_MILLISEC(cur_time);
+
+           /* Have we crossed the timeout threshold? */
+           if (cur_timeout <= 0)
+               return true;
+       }
+   }
 }
 
 /*

diff --git a/src/include/storage/condition_variable.h b/src/include/storage/condition_variable.h
index 2a0249392ccc98dbc9bbea21726346248a6d8c78..ee06e051ce1246ec8511d5bda433327223613622 100644 (file)
--- a/src/include/storage/condition_variable.h
+++ b/src/include/storage/condition_variable.h
@@ -43,6 +43,8 @@ extern void ConditionVariableInit(ConditionVariable *cv);
  * the condition variable.
  */
 extern void ConditionVariableSleep(ConditionVariable *cv, uint32 wait_event_info);
+extern bool ConditionVariableTimedSleep(ConditionVariable *cv, long timeout,
+                                       uint32 wait_event_info);
 extern void ConditionVariableCancelSleep(void);
 
 /*