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d95d61b1af
* Better refcounting Cribbed from [Rust Arc][1] and the [Boost docs][2]: """ Increasing the reference counter can always be done with memory_order_relaxed: New references to an object can only be formed from an existing reference, and passing an existing reference from one thread to another must already provide any required synchronization. It is important to enforce any possible access to the object in one thread (through an existing reference) to happen before deleting the object in a different thread. This is achieved by a "release" operation after dropping a reference (any access to the object through this reference must obviously happened before), and an "acquire" operation before deleting the object. It would be possible to use memory_order_acq_rel for the fetch_sub operation, but this results in unneeded "acquire" operations when the reference counter does not yet reach zero and may impose a performance penalty. """ [1] https://moshg.github.io/rust-std-ja/src/alloc/arc.rs.html [2] https://www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html * Make ZiposHandle's pos atomic Implements a somewhat stronger guarantee than POSIX specifies: reads and seeks are atomic. They may be arbitrarily reordered between threads, but each one happens all the way and leaves the fd in a consistent state. This is achieved by "locking" pos in __zipos_read by storing SIZE_MAX to pos during the operation, so only one can be in-flight at a time. Seeks, on the other hand, just update pos in one go, and rerun if it changed in the meantime. I used `LIKELY` / `UNLIKELY` to pessimize the concurrent case; hopefully that buys back some performance.
64 lines
1.8 KiB
C
64 lines
1.8 KiB
C
#ifndef COSMOPOLITAN_LIBC_ZIPOS_ZIPOS_H_
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#define COSMOPOLITAN_LIBC_ZIPOS_ZIPOS_H_
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COSMOPOLITAN_C_START_
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#define ZIPOS_PATH_MAX 1024
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#define ZIPOS_SYNTHETIC_DIRECTORY 0
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struct stat;
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struct iovec;
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struct Zipos;
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struct ZiposUri {
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uint32_t len;
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char path[ZIPOS_PATH_MAX];
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};
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struct ZiposHandle {
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struct ZiposHandle *next;
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struct Zipos *zipos;
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size_t size;
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size_t mapsize;
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size_t cfile;
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_Atomic(int) refs;
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_Atomic(size_t) pos;
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uint8_t *mem;
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uint8_t data[];
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};
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struct Zipos {
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long pagesz;
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uint8_t *map;
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uint8_t *cdir;
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uint64_t dev;
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size_t *index;
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size_t records;
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struct ZiposHandle *freelist;
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};
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int __zipos_close(int);
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void __zipos_free(struct ZiposHandle *);
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struct ZiposHandle *__zipos_keep(struct ZiposHandle *);
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struct Zipos *__zipos_get(void) pureconst;
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size_t __zipos_normpath(char *, const char *, size_t);
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ssize_t __zipos_find(struct Zipos *, struct ZiposUri *);
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ssize_t __zipos_scan(struct Zipos *, struct ZiposUri *);
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ssize_t __zipos_parseuri(const char *, struct ZiposUri *);
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uint64_t __zipos_inode(struct Zipos *, int64_t, const void *, size_t);
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int __zipos_open(struct ZiposUri *, int);
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void __zipos_postdup(int, int);
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int __zipos_access(struct ZiposUri *, int);
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int __zipos_stat(struct ZiposUri *, struct stat *);
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int __zipos_fstat(struct ZiposHandle *, struct stat *);
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int __zipos_stat_impl(struct Zipos *, size_t, struct stat *);
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ssize_t __zipos_read(struct ZiposHandle *, const struct iovec *, size_t,
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ssize_t);
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int64_t __zipos_seek(struct ZiposHandle *, int64_t, unsigned);
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int __zipos_fcntl(int, int, uintptr_t);
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int __zipos_notat(int, const char *);
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void *__zipos_mmap(void *, uint64_t, int32_t, int32_t, struct ZiposHandle *,
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int64_t);
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COSMOPOLITAN_C_END_
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#endif /* COSMOPOLITAN_LIBC_ZIPOS_ZIPOS_H_ */
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