55 lines
2.4 KiB
Zig
55 lines
2.4 KiB
Zig
//! Inter-process communication: message-passing channels.
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//!
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//! IPC is the backbone of a microkernel ([vision](../docs/vision.md)): once
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//! drivers and services live in separate address spaces, a message is how they
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//! talk. This first form is a **bounded blocking channel** — a ring buffer of
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//! messages with a producer/consumer rendezvous, built on the scheduler's
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//! [wait queues](scheduling.md). `send` blocks when the channel is full, `receive`
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//! blocks when it's empty; neither busy-waits.
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//!
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//! For now both endpoints are kernel threads sharing the kernel address space.
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//! When user mode arrives, the same primitive carries messages across the
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//! isolation boundary (with the payload copied between address spaces).
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const scheduler = @import("scheduler.zig");
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const sync = @import("sync.zig");
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/// A bounded blocking channel of `capacity` messages of type `T`.
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pub fn Channel(comptime T: type, comptime capacity: usize) type {
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return struct {
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const Self = @This();
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buffer: [capacity]T = undefined,
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head: usize = 0, // next slot to read
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tail: usize = 0, // next slot to write
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count: usize = 0,
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not_full: scheduler.WaitQueue = .{}, // senders wait here
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not_empty: scheduler.WaitQueue = .{}, // receivers wait here
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/// Send a message, blocking while the channel is full.
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pub fn send(self: *Self, message: T) void {
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const flags = sync.enter();
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// Recheck the condition in a loop: a wakeup only means "try again"
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// (another waiter may have taken the slot first).
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while (self.count == capacity) scheduler.waitLocked(&self.not_full);
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self.buffer[self.tail] = message;
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self.tail = (self.tail + 1) % capacity;
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self.count += 1;
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scheduler.wakeLocked(&self.not_empty); // a receiver can now proceed
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sync.leave(flags);
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}
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/// Receive a message, blocking while the channel is empty.
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pub fn receive(self: *Self) T {
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const flags = sync.enter();
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while (self.count == 0) scheduler.waitLocked(&self.not_empty);
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const message = self.buffer[self.head];
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self.head = (self.head + 1) % capacity;
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self.count -= 1;
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scheduler.wakeLocked(&self.not_full); // a sender can now proceed
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sync.leave(flags);
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return message;
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}
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};
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}
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