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Reserve zero as an invalid DSM handle.

Previously, the handle for the control segment could not be zero, butsome other DSM segment could potentially have a handle value of zero.However, that means that if someone wanted to store a dsm_handle thatmight or might not be valid, they would need a separate boolean tokeep track of whether the associated value is legal. That's annoying,so change things so that no DSM segment can ever have a handle of 0 -or as we call it here, DSM_HANDLE_INVALID.Thomas Munro. This was submitted as part of a much larger patch toadd an malloc-like allocator for dynamic shared memory, but this partseems like a good idea independently of the rest of the patch.

1 parent0a74819 commitb40b4ddCopy full SHA for b40b4dd

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2 files changed

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lines changed

src
- backend/storage/ipc
  - dsm.c
- include/storage
  - dsm.h

2 files changed

-1

lines changed

`‎src/backend/storage/ipc/dsm.c‎`

Lines changed: 3 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -182,7 +182,7 @@ dsm_postmaster_startup(PGShmemHeader *shim)`
`182`	`182`	`Assert(dsm_control_address==NULL);`
`183`	`183`	`Assert(dsm_control_mapped_size==0);`
`184`	`184`	`dsm_control_handle=random();`
`185`		`-if (dsm_control_handle==0)`
	`185`	`+if (dsm_control_handle==DSM_HANDLE_INVALID)`
`186`	`186`	`continue;`
`187`	`187`	`if (dsm_impl_op(DSM_OP_CREATE,dsm_control_handle,segsize,`
`188`	`188`	`&dsm_control_impl_private,&dsm_control_address,`
`@@ -476,6 +476,8 @@ dsm_create(Size size, int flags)`
`476`	`476`	`{`
`477`	`477`	`Assert(seg->mapped_address==NULL&&seg->mapped_size==0);`
`478`	`478`	`seg->handle=random();`
	`479`	`+if (seg->handle==DSM_HANDLE_INVALID)/* Reserve sentinel */`
	`480`	`+continue;`
`479`	`481`	`if (dsm_impl_op(DSM_OP_CREATE,seg->handle,size,&seg->impl_private,`
`480`	`482`	`&seg->mapped_address,&seg->mapped_size,ERROR))`
`481`	`483`	`break;`

`‎src/include/storage/dsm.h‎`

Lines changed: 3 additions & 0 deletions

Original file line number	Diff line number	Diff line change
`@@ -19,6 +19,9 @@ typedef struct dsm_segment dsm_segment;`
`19`	`19`
`20`	`20`	`#defineDSM_CREATE_NULL_IF_MAXSEGMENTS0x0001`
`21`	`21`
	`22`	`+/* A sentinel value for an invalid DSM handle. */`
	`23`	`+#defineDSM_HANDLE_INVALID 0`
	`24`	`+`
`22`	`25`	`/* Startup and shutdown functions. */`
`23`	`26`	`structPGShmemHeader;/* avoid including pg_shmem.h */`
`24`	`27`	`externvoiddsm_cleanup_using_control_segment(dsm_handleold_control_handle);`

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Commitb40b4dd

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2 files changed

2 files changed

`‎src/backend/storage/ipc/dsm.c‎`

`‎src/include/storage/dsm.h‎`

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