1 files changed, 120 insertions, 0 deletions
diff --git a/src/backend/storage/file/sharedfileset.c b/src/backend/storage/file/sharedfileset.c
new file mode 100644
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--- /dev/null
+++ b/src/backend/storage/file/sharedfileset.c
@@ -0,0 +1,120 @@
+/*-------------------------------------------------------------------------
+ *
+ * sharedfileset.c
+ *	  Shared temporary file management.
+ *
+ * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/storage/file/sharedfileset.c
+ *
+ * SharedFileSets provide a temporary namespace (think directory) so that
+ * files can be discovered by name, and a shared ownership semantics so that
+ * shared files survive until the last user detaches.
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include <limits.h>
+
+#include "catalog/pg_tablespace.h"
+#include "commands/tablespace.h"
+#include "common/hashfn.h"
+#include "miscadmin.h"
+#include "storage/dsm.h"
+#include "storage/ipc.h"
+#include "storage/sharedfileset.h"
+#include "utils/builtins.h"
+
+static void SharedFileSetOnDetach(dsm_segment *segment, Datum datum);
+
+/*
+ * Initialize a space for temporary files that can be opened by other backends.
+ * Other backends must attach to it before accessing it.  Associate this
+ * SharedFileSet with 'seg'.  Any contained files will be deleted when the
+ * last backend detaches.
+ *
+ * Under the covers the set is one or more directories which will eventually
+ * be deleted.
+ */
+void
+SharedFileSetInit(SharedFileSet *fileset, dsm_segment *seg)
+{
+	/* Initialize the shared fileset specific members. */
+	SpinLockInit(&fileset->mutex);
+	fileset->refcnt = 1;
+
+	/* Initialize the fileset. */
+	FileSetInit(&fileset->fs);
+
+	/* Register our cleanup callback. */
+	if (seg)
+		on_dsm_detach(seg, SharedFileSetOnDetach, PointerGetDatum(fileset));
+}
+
+/*
+ * Attach to a set of directories that was created with SharedFileSetInit.
+ */
+void
+SharedFileSetAttach(SharedFileSet *fileset, dsm_segment *seg)
+{
+	bool		success;
+
+	SpinLockAcquire(&fileset->mutex);
+	if (fileset->refcnt == 0)
+		success = false;
+	else
+	{
+		++fileset->refcnt;
+		success = true;
+	}
+	SpinLockRelease(&fileset->mutex);
+
+	if (!success)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("could not attach to a SharedFileSet that is already destroyed")));
+
+	/* Register our cleanup callback. */
+	on_dsm_detach(seg, SharedFileSetOnDetach, PointerGetDatum(fileset));
+}
+
+/*
+ * Delete all files in the set.
+ */
+void
+SharedFileSetDeleteAll(SharedFileSet *fileset)
+{
+	FileSetDeleteAll(&fileset->fs);
+}
+
+/*
+ * Callback function that will be invoked when this backend detaches from a
+ * DSM segment holding a SharedFileSet that it has created or attached to.  If
+ * we are the last to detach, then try to remove the directories and
+ * everything in them.  We can't raise an error on failures, because this runs
+ * in error cleanup paths.
+ */
+static void
+SharedFileSetOnDetach(dsm_segment *segment, Datum datum)
+{
+	bool		unlink_all = false;
+	SharedFileSet *fileset = (SharedFileSet *) DatumGetPointer(datum);
+
+	SpinLockAcquire(&fileset->mutex);
+	Assert(fileset->refcnt > 0);
+	if (--fileset->refcnt == 0)
+		unlink_all = true;
+	SpinLockRelease(&fileset->mutex);
+
+	/*
+	 * If we are the last to detach, we delete the directory in all
+	 * tablespaces.  Note that we are still actually attached for the rest of
+	 * this function so we can safely access its data.
+	 */
+	if (unlink_all)
+		FileSetDeleteAll(&fileset->fs);
+}