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db_include/storage/condition_variable.h

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+/*-------------------------------------------------------------------------
+ *
+ * condition_variable.h
+ *	  Condition variables
+ *
+ * A condition variable is a method of waiting until a certain condition
+ * becomes true.  Conventionally, a condition variable supports three
+ * operations: (1) sleep; (2) signal, which wakes up one process sleeping
+ * on the condition variable; and (3) broadcast, which wakes up every
+ * process sleeping on the condition variable.  In our implementation,
+ * condition variables put a process into an interruptible sleep (so it
+ * can be canceled prior to the fulfillment of the condition) and do not
+ * use pointers internally (so that they are safe to use within DSMs).
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/storage/condition_variable.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef CONDITION_VARIABLE_H
+#define CONDITION_VARIABLE_H
+
+#include "storage/proclist_types.h"
+#include "storage/spin.h"
+
+typedef struct
+{
+	slock_t		mutex;			/* spinlock protecting the wakeup list */
+	proclist_head wakeup;		/* list of wake-able processes */
+} ConditionVariable;
+
+/*
+ * Pad a condition variable to a power-of-two size so that an array of
+ * condition variables does not cross a cache line boundary.
+ */
+#define CV_MINIMAL_SIZE		(sizeof(ConditionVariable) <= 16 ? 16 : 32)
+typedef union ConditionVariableMinimallyPadded
+{
+	ConditionVariable cv;
+	char		pad[CV_MINIMAL_SIZE];
+} ConditionVariableMinimallyPadded;
+
+/* Initialize a condition variable. */
+extern void ConditionVariableInit(ConditionVariable *cv);
+
+/*
+ * To sleep on a condition variable, a process should use a loop which first
+ * checks the condition, exiting the loop if it is met, and then calls
+ * ConditionVariableSleep.  Spurious wakeups are possible, but should be
+ * infrequent.  After exiting the loop, ConditionVariableCancelSleep must
+ * be called to ensure that the process is no longer in the wait list for
+ * 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);
+
+/*
+ * Optionally, ConditionVariablePrepareToSleep can be called before entering
+ * the test-and-sleep loop described above.  Doing so is more efficient if
+ * at least one sleep is needed, whereas not doing so is more efficient when
+ * no sleep is needed because the test condition is true the first time.
+ */
+extern void ConditionVariablePrepareToSleep(ConditionVariable *cv);
+
+/* Wake up a single waiter (via signal) or all waiters (via broadcast). */
+extern void ConditionVariableSignal(ConditionVariable *cv);
+extern void ConditionVariableBroadcast(ConditionVariable *cv);
+
+#endif							/* CONDITION_VARIABLE_H */