diff options
| author | Robert Haas | 2016-11-15 21:30:35 +0000 |
|---|---|---|
| committer | Robert Haas | 2016-11-15 21:33:29 +0000 |
| commit | b40b4dd9e10ea701c8d47ccba9407fc32ed384e5 (patch) | |
| tree | 97a6bd5f4ba10dcecd8a0f3900c4cbe37be8dbd5 | |
| parent | 0a7481930c788e9d74a154aac0c8b401fc6a81f9 (diff) | |
Reserve zero as an invalid DSM handle.
Previously, the handle for the control segment could not be zero, but
some other DSM segment could potentially have a handle value of zero.
However, that means that if someone wanted to store a dsm_handle that
might or might not be valid, they would need a separate boolean to
keep 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 to
add an malloc-like allocator for dynamic shared memory, but this part
seems like a good idea independently of the rest of the patch.
| -rw-r--r-- | src/backend/storage/ipc/dsm.c | 4 | ||||
| -rw-r--r-- | src/include/storage/dsm.h | 3 |
2 files changed, 6 insertions, 1 deletions
diff --git a/src/backend/storage/ipc/dsm.c b/src/backend/storage/ipc/dsm.c index d8066647a0..8c6abe3b45 100644 --- a/src/backend/storage/ipc/dsm.c +++ b/src/backend/storage/ipc/dsm.c @@ -182,7 +182,7 @@ dsm_postmaster_startup(PGShmemHeader *shim) Assert(dsm_control_address == NULL); Assert(dsm_control_mapped_size == 0); dsm_control_handle = random(); - if (dsm_control_handle == 0) + if (dsm_control_handle == DSM_HANDLE_INVALID) continue; if (dsm_impl_op(DSM_OP_CREATE, dsm_control_handle, segsize, &dsm_control_impl_private, &dsm_control_address, @@ -476,6 +476,8 @@ dsm_create(Size size, int flags) { Assert(seg->mapped_address == NULL && seg->mapped_size == 0); seg->handle = random(); + if (seg->handle == DSM_HANDLE_INVALID) /* Reserve sentinel */ + continue; if (dsm_impl_op(DSM_OP_CREATE, seg->handle, size, &seg->impl_private, &seg->mapped_address, &seg->mapped_size, ERROR)) break; diff --git a/src/include/storage/dsm.h b/src/include/storage/dsm.h index 8be7c9aeeb..bc91be6213 100644 --- a/src/include/storage/dsm.h +++ b/src/include/storage/dsm.h @@ -19,6 +19,9 @@ typedef struct dsm_segment dsm_segment; #define DSM_CREATE_NULL_IF_MAXSEGMENTS 0x0001 +/* A sentinel value for an invalid DSM handle. */ +#define DSM_HANDLE_INVALID 0 + /* Startup and shutdown functions. */ struct PGShmemHeader; /* avoid including pg_shmem.h */ extern void dsm_cleanup_using_control_segment(dsm_handle old_control_handle); |